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© 2010 COMSOL, INC. 2010. COMSOL, COMSOL MULTIPHYSICS, COMSOL REACTION ENGINEERING LAB, AND FEMLAB ARE REGISTERED TRADEMARKS OF COMSOL AB. physicsworld.com Contents: May 2010

Quanta 3 Frontiers 4 Strange mass pinned down ● A visible quantum effect ● 3D object optically cloaked ● Controlling light on the nano-scale ● Pure water for disaster victims News & Analysis 7

GIPhotoStock/Science Photo Library LHC physics programme begins ● Report warns of NIF ignition delays ● Underwater solution for storing wind energy ● China boosts nuclear power ● Obama outlines NASA vision ● Europe launches ice mission ● UK announces first space agency ● Mystery over Iranian physicist ● US unveils nuclear-weapons plan ● Science in the Shine on – the laser in everyday life 16–20 UK general election ● A laser to break the vacuum Feedback 14 Itsy-bitsy units and comments from physicsworld.com The laser at 50 From ray-gun to Blu-ray 16 Sidney Perkowitz reveals how lasers in fiction have kept up with lasers in fact – or is it

Patrick Landmann/Science Photo Library the other way round? And then there was light 23 The laser’s early years were full of scientific creativity, public-relations spin and Laser quest – bridging the green gap 43–45 intense rivalry, as Pauline Rigby describes Fusion’s bright new dawn 28 Mike Dunne explains how a much anticipated breakthrough in laser fusion could transform the search for abundant, carbon-free electricity Timeline: light fantastic 34 Highlighting a few of the applications, awards and “firsts” in the laser’s rich history The bubble legacy 36

Max Planck Institute of Quantum Optics The telecoms crash of the early 2000s may have been a turbulent time for investors, but several key laser-based technologies from that period have been hugely successful. Jeff Hecht reports

Fast forward – attosecond light pulses 47–51 Going for green 43 Mobile-phone companies want scientists to devise green laser diodes with powers of at least 50 mW. Andy Extance explains why, and reveals the competing physical On the cover phenomena – and companies – involved in this race The laser at 50 (Kate Gardner, Louise Mayor and Dens Milne) 15–56 Beyond ultrafast 47 Adrian Cavalieri tells us how to create laser pulses as short as 80 attoseconds, and highlights some of the ultrafast physical processes these pulses can reveal Where next for the laser? 53 Six experts review the past and predict the future of lasers in different areas of physics Physics World is published monthly as 12 issues per annual volume by IOP Publishing Ltd, Dirac House, Temple Back, Bristol BS1 6BE, UK Careers 58 United States Postal Identification Statement Supporting laser science Harald Ellmann ● Once a physicist: Fausto Morales Physics World (ISSN 0953-8585) is published monthly by IOP Publishing Ltd, Dirac House, Temple Back, Bristol BS1 6BE, UK. Annual subscription price is US $585. Air freight and mailing Recruitment 62 in the USA by Publications Expediting, Inc., 200 Meacham Ave, Elmont NY 11003. Periodicals postage at Jamaica NY 11431. US Postmaster: send address changes to Physics World, American Institute of Physics, Suite 1NO1, Lateral Thoughts 68 2 Huntington Quadrangle, Melville, NY 11747-4502 A villain’s life in lasers Kate Oliver 1 Physics World May 2010 physicsworld.com Quanta

For the record Seen and heard The possibility for discovery is off the chart Students on the course can look forward to demonstrations from the chefs on, for Nobel laureate Sam Ting quoted in the Observer example, how to make bubbles of air Ting’s $300m Alpha Magnetic Spectrometer, surrounded by a thin sheet of fluid, which which will attempt to discover the origin of high- are the inspiration for Adrià’s speciality energy cosmic rays, will finally get a trip to the foams of beetroot, mushroom and International Space Station towards the end of the Transport for London 2005 expresso. Whether Harvard students will year on one of the final Space Shuttle launches. now be rustling up Adrià’s signature dishes – intertwined carrot chips with lemon It is very difficult; it is really difficult verbena, ginger and liquorice followed by melon caviar – remains to be seen. NASA boss Charles Bolden talking to the BBC Bolden was close to tears during an interview when The jokes are on CERN Lambs for the chop asked to reflect on his time as an astronaut and to With the Large Hadron Collider (LHC) If you read the Sun, then you might be describe what it means to him to witness the end having just recorded it first high-energy forgiven for thinking that the laser is not a of the shuttle programme, which has run for more collisions, the CERN particle-physics lab human invention. According to a report in than 30 years. near Geneva was, perhaps not surprisingly, the paper last month, some UK farmers the main focus of last month’s physics- near Shrewsbury believe that advanced It is extraordinary that this action has based April fool gags. The Independent, alien civilizations have been using lasers to cost £200 000 to establish the rather lamely, claimed that a successor to attack their sheep. Former steelworker the LHC – dubbed LHC II – was earmarked Phil Hoyle, who has spent a decade meaning of a few words to go in the 23 km circumference Circle line investigating unexplained livestock deaths Science writer and physicist Simon Singh quoted of the London Underground. Meanwhile, in the area, says the attacks are being in the Guardian technology website CNET UK announced carried out by two orange-coloured spheres Singh penned a comment piece for the Guardian in that a man had been arrested at the LHC that zap the sheep and remove their brains April 2008 criticizing the British Chiropractic after having travelled back in time to try and eyes. “The animals are being clinically Association (BCA) for claiming its members could and prevent the collider from starting up and surgically sampled by a highly use spinal manipulation to treat children with ear and destroying the world. Keen not to miss advanced technology,” an alarmed Hoyle infections, asthma and other ailments. The BCA out, a CERN press release noted the LHC told the newspaper. Having interviewed then sued him for libel denying these criticisms. had made its first discovery since it collided farmers, he notes that “all but one” had Last month Singh won the right to use “fair protons at 3.5TeV per beam on 30 March. experienced the disappearance or strange comment” in his defence. The release claimed that two researchers death of one of their animals. Hoyle offers had found a paleoparticle, nicknamed no explanation for the aliens’ prowess with It is a very low bar – there is basically “neutrinosaurus” because of its lasers but says that the devices must be built me and Patrick Moore “prehistoric origins”. Yawn. Possibly the “by technology and intelligence that’s not best April fool was by physicist from here”. The mystery continues. Particle physicist and broadcaster Brian Cox Adam Falkowski from Rutgers University, quoted in the Daily Mail who announced on his blog Resonaances Buzz off ABC Cox, who came 70th in People magazine’s that the “unmistakable” tracks of a He may have been the 100 sexiest men of the year, comes over all supersymmetric particle had been found second man to step on the modest when praised for being “good-looking…for by the ATLAS detector at CERN. At least Moon, but Buzz Aldrin a scientist”. one Nature reporter fell for the gag and probably spent more time double-checked with CERN if the on the lunar surface than I have never forgiven them – my discovery was true. Now that is funny. he did on the US TV show German is still pitiful Dancing with the Stars. Physics à la carte The 80-year-old former astronaut became Queen guitarist Brian May quoted in Eureka The culinary limit of most university the second celebrity to be voted off the May, who finally completed his PhD in physics students is probably beans on toast, show last month and recorded the week’s astrophysics in 2007, still regrets being forced to with, if they are feeling especially creative, lowest score from the judging panel. study German at school on the grounds that it a splash of chilli sauce on top. But students Despite training for five hours a day before would help him to understand physics papers by at Harvard University might be rustling up his stage debut, Aldrin gained only German researchers. something much more exciting in the 13 points out of 30 for his waltz, which he future. This autumn the renowned chef performed with dance partner Ashly Costa. They have been a breath of fresh air Ferran Adrià, from the world famous, However, Aldrin’s appearance had an three-Michelin-starred restaurant El Bulli ulterior motive – to promote the US space Environmentalist James Lovelock quoted in in northern Spain, will begin teaching programme and its future direction. The Times culinary physics at the university. Over a “[I did] the best I could to spread interest Lovelock says that climate sceptics have kept 13-week term, Adrià will team up with among Americans and the rest of the everyone from regarding the science of climate fellow Spanish chef José Andrés to help world about the achievements of success change as a religion. students get to grips with the required that I was a part of in the past,” he told parameters to make a decent dish. Entertainment Weekly. 3 Physics World May 2010 physicsworld.com Frontiers In brief Strange quark weighs in precisely Element 117 created Scientists in Russia and the US have created a new behaviour with calculations based on quan- element with 117 protons by firing calcium-48 tum chromodynamics (QCD), the theory of ions at a target of berkelium-249. Although nuclear the strong force, to define the mass of single physicists had previously synthesized a total of quarks. Refinements to this theory over the Christine Davies 27 elements heavier than uranium, element 117 years have enabled physicists to calculate the had remained elusive because the target material mass of the heavier three quarks – the top, needed to produce it – berkelium-249 – is so bottom and charm – to an accuracy of 99%. difficult to make. The researchers managed, Unfortunately, it is has been much more dif- however, to produce 22 mg of it by intense neutron ficult to make accurate predictions for the irradiation over two years, which they then fired mass of the three lighter quarks – the up, calcium-48 ions at over a 150 day period. The new down and strange – so reference tables still element is the most neutron-rich isotope yet Elementary stuff “Strange” quarks are the heaviest of contain errors of up to 30%. produced, but its half-life of 78 ms is 87 times the three light quarks. Christine Davies at the University of Glas- longer than a previously discovered isotope gow and colleagues in the High Precision containing one neutron less. This supports the idea A collaboration of particle physicists in QCD Collaboration have, however, taken that neutron-rich superheavy nuclei could be Europe and North America has calculated a different approach, known as “lattice extremely stable (Phys. Rev. Lett. at press). the mass of strange quarks to an accuracy of QCD”. The technique, which requires the better than 2% – beating previous results by use of supercomputers, enables theorists to Gravitational waves within sight a factor of 10. This is the first time that the confine the highly nonlinear strong interac- Fluctuations in the curvature of space–time known mass of one of the lighter quarks has been tion by defining quarks as nodes on a grid as gravitational waves could be discovered within a constrained to such accuracy and could help and gluons as the connecting lines. Davies’ year of current detectors being upgraded, provided experimentalists to scrutinize the Standard team adapts lattice QCD to calculate a ratio that the detectors focus their search on emissions Model of particle physics. of the mass of the charm quark to the mass from binary black holes. That is the view of It is notoriously difficult to determine the of the strange quark. As the charm mass is astrophysicists in Poland, who believe there are mass of quarks because these elementary well known, the researchers can estimate the significantly more of these astrophysical systems particles never exist in isolation – instead the strange quark mass to be 92.4 ± 2.5 MeV/c2 than was previously thought. After analysing data strong force constrains them into bound (arXiv:0910.3102v2). from the Sloan Digital Survey, the researchers states called hadrons, such as the proton and The result will be of particular interest to found that 50% of stars in a sample of 300 000 the neutron. The picture is complicated be- researchers at CERN’s LHCb experiment, galaxies have a lower “metallicity” than the Sun, cause a large portion of the hadron mass is who, by studying mesons made of bottom which makes them much more likely to form believed to belong to the strong force itself, quarks, are trying to recreate conditions from black-hole binaries as they lose less mass at the mediated by particles known as gluons, and shortly after the Big Bang. “This is all part of end of their lives. Upgrades to the LIGO and VIRGO the exact nature of gluon–quark interactions pinning down the Standard Model and ask- experiments, to be completed by 2015, should give is poorly understood. Theorists therefore ing how nature can tell the difference be - them the sensitivity to detect these gravitational have to combine measurements of hadron tween matter and antimatter,” says Davies. waves “within the first year of operation”, claim the researchers (arXiv:1004.0386). to reach its ground state is proportional to its I spy quantum behaviour frequency. As the aluminium-based “quan- Wonder material steals the light tum drum” used in the UCSB experiment Researchers at IBM have made the first Physicists in the US have observed quantum resonates at about six billion vibrations per photodetector from graphene – a sheet of carbon behaviour in a macroscopic object large second, it could reach this resonation state just one atom thick. Photodetectors convert optical enough to be seen with the naked eye – a thin at “just” 0.1 K. “A regular tuning fork, for signals into electrical current and they are widely disc-shaped mechanical resonator measuring example, would need to be cooled by an- used in communications and sensing. The about 6.25 mm × 6.25 mm and consisting of other factor of a million to reach the same researchers needed to overcome a rare flaw in around a trillion atoms. In making their ob- state,” says Cleland. graphene: the electrons and holes in the bulk of servations, Andrew Cleland and colleagues The team measured the quantum state of the material recombine too quickly, which leaves at the University of California, Santa Barbara the resonator by connecting it electrically to no free electrons to carry current. They applied an (UCSB) have exploited one of the funda- a superconducting quantum bit, or “qubit”, internal electric field via palladium or titanium mental principles of quantum mechanics – that was used to excite a single phonon in the electrodes that are on top of multilayered or objects being in two states at the same time. resonator. This excitation was then trans- single-layered graphene, which separates the To achieve these “superposition states”, ferred many times between the resonator electrons and holes. The graphene photodetector an object needs to be cooled down to its and qubit to enable the researchers to create can detect optical data at rates of 10 Gbit s–1; this quantum ground state, at which point the a superposition state in the resonator where compares well with optical networks made of other amplitude of its vibrations is reduced to close an excitation and a lack of excitation existed materials, such as group III–V semiconductors to zero. Until now, such states have only simultaneously. When the researchers meas - (Nature Photonics 10.1038/nphoton.2010.40). been induced in objects up to the atomic ured the state, via the qubit, the resonator scale and some larger molecules, such as had to “choose” which state it was in (Nature Read these articles in full and sign up for free “buckyballs”, which are made up of 60 car- 464 697). The experiment could enable re- e-mail news alerts at physicsworld.com bon atoms. However, the temperature to searchers to study the boundaries between which an object needs to be cooled in order the quantum and classical worlds. 4 Physics World May 2010 physicsworld.com Frontiers

Innovation

Science /AAAS Tiny desalination device could help aid efforts

Each year, two million people – mostly children – die from water-borne diseases such as diarrhoea and cholera, according to the United Nations. Particularly vulnerable are those affected by natural disasters, when gaining access to clean water can be a problem. However, a new technique that produces drinking water from seawater using just small amounts of energy could help to address this dire situation. The technique, developed by researchers at the Massachusetts Institute of Technology (MIT) in the US and Pohang University of Science and 3D invisibility cloak unveiled Technology in Korea, manages to desalinate water While this dented cuboid may not look particularly magical, it represents a key breakthrough in one of the using a simple electronic system. The process more mind-bending areas of physics – the pursuit of invisibility. It is the first device that can hide an object starts by passing water along a tiny, 500 μm wide from near-visible light in three dimensions – albeit a very small bump with a height of just 30 μm. The channel on a polymer chip. When the water design is known as a “carpet cloak” because it involves smoothing out a bump on a surface as if flattening reaches a junction, it splits off into two separate out a ruck in a rug. The cloak was fabricated by Tolga Ergin and colleagues at the Karlsruhe Institute of tubes. By applying an electric potential along one Technology (KIT) in Germany, together with John Pendry of Imperial College London. The team built the of these tubes, salt ions are dragged towards this cloak by stacking nanofabricated silicon wafers on top of one another in a “woodpile” matrix and then channel in the form of brine, while desalinated filling in the gaps between the wafers with varying amounts of polymer. This produces a distribution of water flows down the second channel under the refractive indices within the structure that can achieve an optical transformation whereby light appears to force of gravity. The researchers have successfully reflect off the device as if an object were not there. To demonstrate the technique, the researchers placed used the technique, which is dubbed ion their device on top of a reflective gold surface containing a small bump with dimensions of concentration polarization (ICP), to convert 30 μm × 10 μm × 1 μm. This set-up produced a cloaking effect using unpolarized infrared light with seawater, with a salinity of 30 000 mg l–1, into wavelengths between 1.4 μm and 2.7 μm (Science 10.1126/science.1186351). Importantly, this effect fresh water with a salinity of less than 600 mg l–1, held for viewing angles of up to 60° (with 0° representing viewing in just two dimensions). Last year this which meets the international standards for water same cloaking technique was used to hide objects at micro and infrared wavelengths, but these cloaks purity (Nature Nanotech. 5 297). were limited to two dimensions. Team member Martin Wegener from KIT says that it should be possible In terms of energy consumption, ICP compares with existing technology to make the cloak bigger in order to hide even larger objects, but that this favourably with established methods of approach would be extremely time-consuming. “Faster nanofabrication tools will have to be developed desalination, requiring less than 3.5 Wh l–1. that allow for 3D structures,” he says. Reverse osmosis, for example, which works by forcing seawater through a membrane at high pressures to capture the salt, requires 10– Antenna shrunk for the nanoworld 15 Wh l–1. And electrodialysis, which works by transporting salt ions from one solution to another Nanotechnology in science fiction usually the original signal. The same principle works by means of ion-exchange membranes, requires involves familiar objects being cleverly in reverse, so the antenna can also boost a sig- 5 Wh l–1. Another advantage of ICP is that it can shrunk to the scale of individual molecules. nal when receiving information. remove other potentially harmful larger molecules In a rare example of that vision becoming Yutaka Kadoya and colleagues at Hiro - – such as cells, viruses and bacteria – without the a reality, researchers in Japan have built a shima University have now adapted the filter becoming heavily clogged, a problem that nano-scale version of a classic TV antenna Yagi–Uda design to control light at the nano- affects both reverse osmosis and electrodialysis. but in this case it can transmit light. scale by replacing the conducting strips with The next challenge is to scale up the device into The “Yagi–Uda” antenna was invented by an array of five gold nanorods. The nanorods a viable technology. As one chip produces just Japanese scientists in 1926 to overcome sig- are aligned in such a way that incoming light 10 μl per minute, the researchers estimate that nal degradation, whereby radio signals de- manages to trigger plasmons in the gold sur- they will need 10 000 combined units to produce a grade when transmitted over long distances. face – collective wavelike motions of billions useful amount of water in a realistic time. A device It was used by the British with radar during of electrons – to resonate and emit secondary this size would still be portable at just 30 × 20 cm. the Second World War and went on to be- light in the same direction. The researchers Sung Jae Kim, one of the researchers at MIT, come the standard antenna for transmitting demonstrated the technique for red light with told Physics World that his team hope to have and receiving television signals. Key to the a wavelength of 662 nm (Nature Photonics produced a 100-unit device within two years. classic design is its “parasitic elements”, 10.1038/nphoton.2010.34). They now want to One outstanding challenge is to ensure that all made from strips of electrical conductors, integrate their design with fluorescent mole- dangerous hydrocarbons and heavy metals are which boost radio transmissions by produ- cules to create a coupled device that could also removed from the seawater, which is not cing secondary signals in the same direction form the basis of a new sensing technique for guaranteed with the current device. when a current is induced in the presence of the medical sciences. 5 Physics World May 2010 Glassman Physics World Feb 10 15/1/10 12:04 pm Page 1

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GLASSMAN JAPAN Tel: (045) 902-9988 Fax: (045) 902-2268 www.glassmaneurope.co.uk physicsworld.com News & Analysis LHC ramps up its search for the Higgs

The physics programme at CERN’s lighter than 114 GeV. Large Hadron Collider (LHC) is now CERN Some researchers, however, believe under way and the Geneva lab says it that it could take much longer to is making good progress with increas- prove decisively whether the Higgs ing the number of proton–proton col- does exist. “From previous findings lisions. The first collisions at 7 TeV, at the Tevatron [at Fermilab in the marking the start of the LHC’s phys - US] and theoretical studies, it seems ics programme, occurred on 30 March most probable that the Higgs mass is and all four of the LHC’s experiments a tick above 115 GeV,” says Hanspeter have been collecting data since then. Beck, a researcher at the ATLAS ex - “A lot of people have waited a long peri ment. “And, if it is there, it will be time for this moment, but their pa - ultra difficult [to find] and will take up tience and dedication are starting to to six years to prove or disprove if it pay dividends,” said CERN director- ex ists,” he adds. general Rolf-Dieter Heuer. Meanwhile, Niko Neufeld, a staff Heuer’s delight at the LHC finally scientist at the LHCb experiment, colliding protons 18 months after its spokesperson for the Compact Muon Watchful eyes which will study the difference be- start-up, was shared by Fabiola Gia- Solenoid (CMS) experiment. “We will Staff in CERN’s tween matter and antimatter with un- notti, spokesperson for the ATLAS have our first pop at the Higgs at the control room await precedented accuracy, is optimistic ex periment. “The prevailing senti- end of the year – we will certainly ex- 7 TeV collisions. that it can start producing “serious ment is emotion,” she said shortly clude mass regions but discovery is physics” within a few months. “To- after the first collisions were an- going to be more difficult.” wards the end of this year we should nounced. “Behind these instruments The missing piece in the Standard be in full swing and hopefully have the are people with their feelings, with Model of particle physics, the Higgs first drafts of papers for the winter their frustrations, with their ambitions boson could explain how particles conferences of next year,” he says. – it is the end of 20 years’ hard work acquire their mass. Precision meas- CERN plans to run the LHC con- within the scientific community.” urements of known Standard Model tinuously for 18 to 24 months, with a Researchers at the lab are so far particles mean that the mass of the short technical stop at the end of 2010. pleased with the quality of the collision Higgs is unlikely to be more than The LHC will then shut down in 2012 data they have received. “By autumn, 186 GeV, while direct searches made to prepare it to go to maximum-energy it is going to get quite interesting here at CERN’s Large Electron–Positron 14 TeV collisions, probably in 2013. – we will be frantically looking at the collider (LEP) – the forerunner to the James Dacey data,” says Albert de Roeck, deputy LHC – have ruled out a Higgs that is Geneva

Fusion lashes out at the management of the project. In particular, the report finds that a “weak oversight” by the National Breakthrough at NIF ‘unlikely’ in 2010 Nuclear Security Administration (NNSA) has allowed NIF’s operator, the Lawrence Hopes of reaching a milestone in fusion [We] never the beams will then cause the sphere to Livermore National Laboratory, to delay research by the end of 2010 have dimmed claimed it implode, fusing the deuterium and construction of safety systems required following a US government report that tritium nuclei and setting off a sustained for ignition experiments. These included plays down the chances of an early would achieve burn that produces excess energy concrete doors needed to contain breakthrough and sharply criticizes fusion ignition (see pp28–33). radiation from neutrons produced in management of the $4bn National in 2010 Although a NIF spokesperson told near-ignition reactions. Ignition Facility (NIF). In the report, Physics World that the lab “never claimed The NIF spokesperson says that officials from the Government it would achieve fusion ignition in 2010”, researchers will initially perform Accountability Office (GAO) state that expectations of an early breakthrough diagnostic tests using ordinary hydrogen, ignition – fusion’s “break-even” point – is had been raised in January, after NIF rather than deuterium, to keep neutron “unlikely” to occur at the laser-fusion lab researchers published results showing levels low. The proportion of deuterium this year and that “significant scientific that they could compress plastic test will then be slowly increased, until and technical challenges” could delay or spheres smoothly at radiation conditions are met for a full ignition even prevent the facility from achieving temperatures of up to 3.3 mK. Tests experiment using 50% deuterium and ignition by 2012. performed shortly after the facility 50% tritium. The spokesperson adds that NIF’s plan for ignition relies on being opened in March 2009 had already the “first credible attempts” at fusion able to focus up to 1.8 MJ energy from demonstrated that laser systems could would still begin in 2010, emphasizing 192 laser beams onto a 2 mm-diameter operate at the high energies required. that ignition is still expected within a year beryllium sphere filled with deuterium But while the GAO acknowledges that or two. and tritium fuel. Radiation pressure from “substantial progress” has been made, it Margaret Harris 7 Physics World May 2010 News & Analysis physicsworld.com

Innovation Spin-out puts new spin on wind-energy technology

The future of wind energy could in- Although Garvey believes that it will volve huge blades spanning half a take about 15 years to get the giant kilometre that generate compressed turbines up and running, he says his air – which is then piped into giant, system could be as cheap to build as a underwater balloons. That is the gas-turbine generator and have zero dream of Seamus Garvey, a mechan- fuel costs. University of Nottingham ical engineer at the University of Not- Compressed-air energy storage is tingham in the UK, who envisages not a totally new idea. There are two using the pressurized air to inflate facilities – one in Germany and the the balloons, nestling about 500 m other in the US – where surplus below the surface of the sea. Electri - energy is taken off the electrical grid city could then be generated, when re- and used to pump air underground quired, by releasing the air to drive a into disused salt mines. But Garvey set of turbines. says that underwater storage has two The advantage of Garvey’s tech- benefits. It is not restricted to mine nique is that several days’ worth of locations, plus the pressure in an un- energy could be stored in the balloons falls through the cylinder, compres- Bags of energy dersea bag is constant, which lets tur- while the wind is blowing – and then sing air. However, the blades must not Seamus Garvey from bines generate electricity relatively released when there is no wind. Gar- rotate too fast or else the pistons will the University of efficiently. An underground storage vey has just formed a spin-out com- get pinned to the ends of the blades. Nottingham has facility, in contrast, has a fixed vol- pany called NIMROD Energy to Given that a blade’s rotation speed is designed a way of ume, meaning that the air pressure commercialize the technology, dub- inversely proportional to its length, storing wind energy in drops as air is released. bed Integrated Compressed Air Re- Garvey’s scheme would only be prac- underwater balloons. Garvey also thinks undersea bags newable Energy Systems (ICARES), tical for turbines bigger than about could store surplus energy from nuc- which he has been working on since 230 m in diameter, with 500 m being lear reactors or even natural gas. 2006. He has also received a 7310 000 the ideal size. Jakob Mann, a wind-energy expert at development grant from the energy As for the storage balloons, Garvey Risø National Laboratory in Den- company E.ON. says they should ideally be 20 m in mark, says that the storage technique According to Garvey’s blueprint, diameter and lie anchored 500 m is “worthwhile trying” but warns that the wind turbine’s blades would be below the surface of the sea. He has the undersea nature of the scheme hollow and contain an internal piston. already begun to test prototype “en- could boost the cost. “Offshore is al - When the blade is pointing down- ergy bags” and believes that that a ways expensive,” he says. wards, the piston is at the tip. As the commercial undersea storage system Hamish Johnston blade slowly lifts skywards, the piston will be available by May next year. ● See also page 14

Energy identified 30 possible sites that can accommodate nuclear power stations. China is already building the world’s China plans massive nuclear boost largest single nuclear power plant in Taishan City, on the southern coast of the China has announced plans to generate Power to the people country, close to Hong Kong. The 1.75 GW an extra 100 GW of power from nuclear One of two 1.75 GW Taishan nuclear plant, costing $4.7bn, is reactors – a 12-fold increase in nuclear European Pressurized the first of two European Pressurized capacity. The plans, released in late Reactors that China is Reactors to be built at Taishan and is March by the Energy Bureau of the building in Taishan expected to come online in 2013, with the Chinese National Development and City, near Hong Kong. second following in 2014. Indeed, Reform Commission (NDRC), will see an Sun Youqi, general manager of Chinese additional 75–80 GW of nuclear power National Nuclear Engineering Group coming online by 2020, with a further Company, says that China is already

25 GW of capacity still under construction China Guangdong Nuclear Power Group building more nuclear power capacity at that time. If the country completes its than any other country in the world. plan, then nuclear power will account However, some worry about China’s for about 5% of China’s electricity needs ability to deal with nuclear-fuel by 2020. nuclear power capacity by 40 GW by reprocessing and high-level radioactive Last year, nuclear power capacity in 2020 with a further 18 GW in waste once the reactors are operating. China was 9.08 GW, accounting for only construction. The revised plans almost “We need to pay far more attention now 1.04% of the total power generation in double those figures. to researching techniques into fuel the country, according to the China “We will be building as many as six to post-processing”, says Li Yongjiang, the Electricity Council, which implements eight 1 GW nuclear power plants each former manager of the Qinshan Nuclear government energy policy. Original plans year,” says Mu Zhanying, general manager Power Company. by the NDRC, published in October 2007, of Chinese National Nuclear Engineering Jiao Li announced that China would increase its Group Company. Chinese authorities have Beijing 8 Physics World May 2010 physicsworld.com News & Analysis

Space Obama sets out NASA’s new mission to Mars

US President Barack Obama has an - actually reach space faster and more nounced a new direction for NASA NASA often under this new plan, in ways that that includes plans to send astronauts will help us improve our technological to an asteroid by 2025. Speaking last capacity and lower our costs,” he month at Florida’s Kennedy Space said. “Nobody is more committed to Center, the launching location for human exploration of space than I am. US manned spaceflights, Obama also But we’ve got to do it in a smart way.” called for a new “heavy-lift” rocket The new plans also include mod- design to take astronauts on a mission ernizing the Kennedy Space Center, to orbit Mars by the mid-2030s that as well as upgrading its launch capa- will “eventually” be used to transport bilities. That process should create humans to the Martian surface. more than 2500 extra jobs in the re- In February, the Obama admin- gion, compensating in part for job istration said it was cancelling the losses that will occur due to the plan- Constellation programme – first pro- ned end of the Space Shuttle pro- posed by George W Bush in 2004 – gramme this year. Obama called as to develop new “Ares” rockets that well for NASA and other government would allow astronauts to return to International Space Station (ISS), as One giant leap agencies to develop a plan by 15 Au- the Moon by 2020. Critics argued that a kind of “space lifeboat” to reduce NASA plans to send gust for economic growth and job cre- the decision would surrender US reliance on foreign vehicles for rescue astronauts on a ation in the region. lead ership in space and extinguish missions to the ISS. mission to orbit Mars In his speech, Obama also ex - the country’s vision of exploration. Obama also announced that NASA by the mid-2030s, plained where an additional $6bn Neil Armstrong, the first man to walk will now invest more than $3bn in re - with a landing some over the next five years for NASA will on the Moon, called the decision search on its heavy-lift rocket, with a time after. be spent. First announced in his 2011 “devastating” and a waste of the design expected to be complete “no budget request to Congress, this new $10bn in vestment in Con stellation later” than 2015. The rocket, which money will go on increasing Earth- and the years of research and devel- should be complete a few years later, based observations, extending the life opment put into the project. could be used for a trip to a near- of the ISS by more than five years to The new plan involves retaining Earth asteroid and then in a separate 2020, as well as working with private some of Constellation’s technology, mission to Mars. companies to make getting to space and NASA will now start to adapt Obama noted that he expects to still easier and more affordable. its Orion crew capsule, which would “be around” by the time US astro- Peter Gwynne have hitched a ride on Ares to the nauts land on the red planet. “We will Boston, MA Europe’s ice mission successfully blasts off

A satellite that will probe how much such as those in the Antarctic and the Antarctic and Greenland ice Greenland. CryoSat-2 is the satellite’s sheets are contributing to global sea- second incarnation after CryoSat-1 level rises was successfully launched P Carril/ESA was destroyed by a launch failure five from the Baikonur Cosmodrome in years ago. In 2006 ESA decided to Kazakhstan last month. The 7135m rebuild the satellite and launch it in CryoSat-2 satellite, built by the Euro - 2009, but delays led to the take-off pean Space Agency (ESA), will also being postponed until last month. measure tiny variations in the thick- “We are very much looking forward ness of ice floating in the polar oceans. to delivering the data the scientific Weighing 700 kg, CryoSat-2 is now community so badly needs to build a orbiting the Earth around its poles true picture of what is happening in 720 km above sea level. the fragile polar regions,” says physi- CryoSat-2’s main instrument is the cist Richard Francis, project manager Synthetic Aperture Interferometric of CryoSat-2. CryoSat-2 is the third of Radar Altimeter (SIRAL), which is Second time lucky centimetres. Researchers can then seven Earth-monitoring satellites that designed to send a burst of microwave The European Space use this information to estimate the form the ESA’s Earth Explorer pro- pulses towards the Earth every 50 µs. Agency’s CryoSat-2 total mass and thickness of ice flow, gramme. The first – the Gravity Field The returning echoes can then be satellite will monitor the bulk of which (some 90%) lies and Steady-state Ocean Circulation used to measure the distance between ice thicknesses. under the water. Explorer (GOCE) – was launched in the satellite and the sea ice, from Set to remain in orbit for the next March 2009, while the Soil Moisture which a 3D map of the thickness of three years, CryoSat-2 will use the and Ocean Salinity (SMOS) space- floating sea ice lying above sea level same technique to measure changes to craft took off last November. can be built to an accuracy of a few the thicknesses of huge land-ice sheets, Michael Banks 9 Physics World May 2010 News & Analysis physicsworld.com

Sidebands Space science

Climate inquiry clears researchers UK launches space agency to manage all contracts “We saw no evidence of any deliberate scientific malpractice in any of the work of A new body that will be responsible 100 000 jobs within the sector over the Climatic Research Unit and had it been for the UK’s space policy and bring the next 20 years. there we believe that it is likely that we all key budgets for space under a The UK currently spends about would have detected it.” That is the main single management was established £300m per year on civil space research, conclusion of an independent panel of last month. The UK Space Agency a large fraction of which – some scientists, nominated by the UK’s (UKSA) will manage about £250m in £240m in 2009 – goes on the country’s Royal Society, to scrutinize the scientific contracts each year, including the membership of the European Space methodology of researchers at the Climate UK’s contribution to major European On the up Agency (ESA). The rest of the cash is Research Unit (CRU) at the University of projects such as the 73.4bn Galileo The UK Space Agency spent on its membership of the Eu ro - East Anglia. The seven-member panel was global positioning system and the will manage about pean Organisation for the Exploi - set up by the university and chaired by Global Monitoring for Environment £250m in contracts tation of Meteorological Satel lites, Lord Oxburgh – a geologist and former and Security initiative. Both projects each year. which launches and maintains Earth- oil-company executive. The report, which are currently supported by the UK’s observation satellites and is currently looked at 11 “representative publications” department for transport, and the de- funded by the UK’s Met Office. from CRU members over the past 24 years, partment for environment, food and At the UKSA launch, Drayson and was commissioned after private CRU rural affairs, respectively. business secretary Lord Mandelson e-mails were hacked last year and made The UKSA, which will have its also announced a £40m International public. Critics alleged that the e-mails headquarters in Swindon, will be led Space Innovation Centre (ISIC) to be showed that the scientists incorrectly by David Williams, director general based at Harwell in Oxfordshire next interpreted data to support man-made of the British National Space Centre, to the European Space Agency’s tech- climate change and flouted freedom-of- until a permanent chief executive is nical facility, which opened last July. information requests to make data and appointed within the next six months. Designed to bring together industry computer code available. “The action we are taking shows that and academia, ISIC will seek to ex- we’re really serious about space,” ploit data from Earth-observation Egypt tops African physics output said science minister Lord Drayson satellites, use space data to under- Egypt, Nigeria and South Africa dominate at the agency’s launch last month. He stand climate change, and advise on scientific output in Africa, according to a claimed that the agency will help the “security and resilience of space new study from Thomson Reuters. It found the UK’s space industry to grow from systems and services”. that researchers in Egypt were the most £6.5bn to £40bn a year and create Michael Banks prolific in the north of the continent, accounting for 30 000 papers between Middle East 1999 and 2008 – three times more than from scientists in Tunisia. Nigeria was the dominant nation in central Africa, Iranian physicist ‘defects’ to the US generating 10 000 papers in the same period, while scientists in South Africa led An Iranian physicist who disappeared last Once you have for nuclear weapons. the way in the south of the continent, June during a pilgrimage to Mecca in acquired the Reza Mansouri, a physicist at Iran’s publishing 47 000 papers in the decade to Saudi Arabia has apparently defected to Sharif University of Technology, told 2008. Egypt is Africa’s top nation for the US, where he is working for the knowledge of Physics World that he had never heard of physics – producing 1880 papers between Central Intelligence Agency (CIA). uranium Amiri’s name before it came to light in the 2004 and 2008. South Africa was second Shahram Amiri, who did research in enrichment, media. “So you can imagine how he stood with 1194 papers and Algeria third with nuclear physics at Malek Ashtar in the physics community in Iran,” he 933 published articles. University of Technology in Tehran, is it is almost says. According to Steven Miller, a thought to be co-operating with the CIA to impossible to specialist on Iran at Harvard University’s Diamond wins £110m upgrade confirm their intelligence assessments remove it Kennedy School of Government, it The Diamond synchrotron light source in about Iran’s nuclear-weapons appears most likely that Amiri the UK has received £110m of funding that programme. The CIA has so far kept quiet disappeared voluntarily. will allow it to complete 10 more on the issue and it remains unclear Amiri is not the first individual with beamlines. The planned upgrade, which whether Amiri had any connections with suspected connections to Iran’s nuclear should be completed by 2017, will bring Iran’s nuclear programme. programme to disappear and reappear in the total number of beamlines at the According to various reports, Amiri was the West. Possibly the best known is facility to 32. The bulk of the money involved in producing radioactive isotopes Ali Reza Ashghari, a former deputy (£97.4m) comes from the Large Facilities for medical applications at Malek Ashtar defence minister, who disappeared from Capital Fund (LFCF), which supports University of Technology. The university a hotel in Istanbul three years ago and investments made by Research Councils lies across the street from FEDAT – an reportedly provided intelligence to the UK – the umbrella organization for the institution run by the country’s Ministry of CIA. But Amiri’s loss is unlikely to affect seven UK funding councils. The remaining Defence that carries out research and the Iranian nuclear programme. “Once £13.8m comes from the Wellcome Trust – development on nuclear weapons. you have acquired the knowledge of a UK-based biomedical charity. Diamond According to the Washington-based uranium enrichment,” says Miller’s currently has 17 operational beamlines, organization Iran Watch, in 2005 officials colleague Jason Blackstock, “it is almost which in two years’ time will be extended in Germany linked the university to work impossible to remove it.” to 22. on proliferation-sensitive nuclear Peter Gwynne activities and the development of rockets Boston, MA 10 Physics World May 2010 physicsworld.com News & Analysis

Policy US changes course on nuclear-weapons strategy

US President Barack Obama has sig- has made a mistake by not supporting nalled a new approach to nuclear- the [production of] reliable replace- weapons policy that limits their use ment warheads,” says Jay Davis,

against other states and documents Chuck Kennedy founding director of the Defense how the country will ensure the viab - Threat Reduction Agency and a for- ility of existing stockpiles. The Nuc- mer Lawrence Livermore National lear Posture Review (NPR), which Laboratory scientist who is now presi- sets out the US’s nuclear strategy dent of the Hertz Foundation. over a 10-year period, also calls for a Immediately following the review, highly skilled workforce to ensure Obama and Russian President Dmitry “the long-term safety, security and Medvedev signed up to the START-II effectiveness of the nuclear arsenal Treaty, which will dramatically reduce and to support the full range of nuc- the number of deployed nuclear lear-security work”. weapons that each country has from The last NPR was conducted in 1762 to 1550 for the US and 1741 to 2001 during the George W Bush ad- highly trained scientists and engin- Signing up 1550 for Russia. Although the Senate ministration, which kept its findings eers to “sustain a safe, secure and US President Barack must ratify the treaty by a two-thirds classified. The latest review, released effective US nuclear stockpile as long Obama and Russian majority before it can come into force, last month and made fully public, con- as nuclear weapons exist”. It also President Dmitry it was welcomed by JASON member cludes that the US will not use nuclear says that existing nuclear weapons’ Medvedev have Sidney Drell, a senior fellow at Stan- weapons against non-nuclear states lifetimes could be increased, ruling signed a new ford University’s Hoover Institution that are “in compliance” with the out the need for manufacturing new agreement on and former deputy director of the Nuc lear Non-proliferation Treaty, “reliable” replacement warheads. nuclear weapons. SLAC National Accelerator Labor at - even if they attack the US with bio- This had been recommended late last ory. “Reducing the reliance on nuclear logical or chemical weapons. How- year by the JASON advisory group – weapons and reaffirming the commit- ever, the review makes it clear that a collection of independent scientists ment to go to zero is a strong and good North Korea and Iran do not fall into who advise the US government on basis,” he says. “And the commitment that category. science issues. to continued support for a science and Carried out by the US Department Some disagree with Obama’s decis- technology base is important.” of Defense and the Department of ion not to update the US’s nuclear Peter Gwynne Energy, the review notes the need for weapons. “I think the administration Boston, MA

UK parties spell out science policies ahead of 6 May general election Conservatives Labour Liberal Democrats Adam Afriyie Paul Drayson Evan Harris Shadow minister for Minister for science and Liberal Democrats innovation, universities innovation spokesperson for science and skills Background: Drayson Background: Evan Harris is a Background: After a BSc in completed a BSc in qualified doctor, having agricultural economics from production engineering at completed his education at Imperial College London, in Aston University in 1982, the Oxford Medical School. 1993 Afriyie became founding director of Connect gaining a PhD in robotics in 1985. After becoming After working as a junior doctor at the Support Services – an IT services company. Afriyie managing director of Lambourn Food Company in Royal Liverpool University Hospital and the was elected as MP for Windsor in 2005. After serving 1986, he co-founded the Oxford-based vaccine John Radcliffe Hospital in Oxford, Harris became an in a range of committees on civil aviation and on company PowderJect Pharmaceuticals in 1993, MP for Oxford West and Abingdon in 1997. In 2001 science and technology, he was made Conservative where he was chairman and chief executive until he became shadow secretary of state for health, parliamentary leader for technology, media and 2003. In October 2008 he was appointed as the and since 2005 he has been the Liberal Democrat telecoms in 2006 and then shadow minister for minister of state for science and innovation, taking spokesperson for science. innovation, universities and skills in 2007. up a seat in the cabinet. In June 2009 he took on Pearls of wisdom: “We recognize that science, Pearls of wisdom: “Our science base is a valuable additional responsibilities as defence minister. technology and engineering have to be key drivers national asset. Economically, politically and Pearls of wisdom: “Science isn’t peripheral to the of our economy as we move out of recession.” socially, it underpins the prosperity and wellbeing decision facing the country. It is central: to growth, What the manifesto says: “In the current economic of our nation.” to prosperity and wellbeing.” climate it is not possible to commit to growth in What the manifesto says: “Initiating a multi-year What the manifesto says: “We are committed spending, but the Liberal Democrats recognize the science and research budget to provide a stable to a ring-fenced science budget in the next importance of science investment to the recovery investment climate for research councils.” spending review.” and to the reshaping of the economy.” Manifesto wordcounts: science/scientists (8); Manifesto wordcounts: science/scientists (6); Manifesto wordcounts: science/scientists (12); innovation (8); research (9); universities (14); innovation (11); research (7); universities (17); innovation (5); research (9); universities (8); physics (0) physics (0) physics (0)

11 Physics World May 2010 News & Analysis physicsworld.com

built within the next decade. Breaking the vacuum The new laser facility quickly gar- nered support with laser scientists in Europe, including Wolfgang Sander, Europe is planning to build the world’s most powerful laser that will director of the Max Born Institute for nonlinear optics and short-pulse literally rip empty space apart. Michael Banks lifts the lid on the spectroscopy in Berlin and the presi- Extreme Light Infrastructure dent-elect of the German Physical Society. “ELI offers a factor of 100 This year is one of celebration for Gér- more in achievable power than any- ard Mourou – and not just because where else in the world,” he says. “A 2010 marks the 50th anniversary of the lot of new physics could be done with invention of the laser. It is also 25 years it – it is revolutionary.” since the 65-year-old French physicist A competition to build ELI was published details of one of his most Hamiltons Architects begun in 2007. Five countries – the coveted contributions to laser science. Czech Republic, France, Hungary, Going by the rather ungainly name of Romania and the UK – initially bid to chirped-pulse amplification (CPA), host the project. But after the UK and the technique has enabled physicists France pulled out of the running, in to create lasers that are orders of mag- October 2009 the ELI steering com- nitudes more powerful than were mittee decided to not build one single achievable without it (see box). facility, but four – one in Romania on CPA now lies at the heart of most nuclear physics, another in Hungary high-powered laser facilities in the on attosecond physics, a third on world. It was used in the now-decom- laser-based particle-beam production missioned Nova PW system at the Four for the future Although ELI will be used for nuc - in the Czech Republic and a fourth in Lawrence Livermore National Labor - The Extreme Light lear physics, attosecond physics and ultrahigh-powered lasers. The latter’s atory in the US, which generated Infrastructure will studies of laser-based particle accel- location is still up for grabs. record-breaking 1.3 PW (1.3 × 1015) consist of four eration, perhaps its most exciting pos- The 7250m needed to build each of pulses, and in the 1 PW Vulcan laser facilities, including sibility is to test the properties of the the first three of these facilities will be at the UK’s Rutherford Appleton La- this one in the vacuum, or empty space, itself. “This met by the host nation and construc- boratory in the UK, which is in the Czech Republic that is not just a laser that is about break- tion is due to start at the end of the midst of being upgraded to go beyond will use short pulses ing the next record,” says Mourou, year. Once up and running in 2015, a the 10 PW level. of light to test who is ELI’s project coordinator and number of European member states But now Mourou is designing a accelerating director of the Institut de la Lu mière belonging to the European Research laser facility that will be so powerful electrons with lasers. Extrême at the Ecole Nation ale Su- Infra struc ture Consortium are ex pec - that it can rip apart empty space itself. périeure de Techniques Avancées in ted to pay for labs’ operational costs. Mourou’s parting shot to the laser France. “There is a fundamental rea- community, the Extreme Light Infra- son be hind building it.” Surfing electrons structure (ELI) will create very short Mourou first proposed ELI five The Czech facility, which will be built pulses of light barely 1 femtosecond years ago and he has been the driving in Prague, will seek to generate for (10–15 s) long with energies of several force behind the project ever since. In the first time pulses with a few peta- kilojoules corresponding to petawatts 2006 it was chosen as one of 35 projects watts in power at a frequency of about of power. While other lasers such as on a “wish list” of scientific facilities 100 Hz. These femtosecond laser pul- Vulcan can provide a high-powered drawn up by the European Strategy ses will be fired into a gas to create an pulse every 20 minutes, ELI will be Forum on Research Infrastructures electron–proton plasma that could be able to deliver one every few minutes. that researchers in Europe want to see used to make a very compact particle Shining light in the femtosecond regime All four sites belonging to the Extreme Light amplified, the refractive index of the medium it is gratings that stretch the pulse in time by a factor of Infrastructure project have one aspect in common: passing through starts to change; and once the a 100 000. The gratings are arranged so that the a way of generating very short pulses of light at power of the beam goes beyond a few gigawatts, it low-frequency component of the laser pulse travels very high energies. At their heart, the four facilities starts to produce nonlinear effects in the medium. a shorter path than the high-frequency component will use the chirped-pulse amplification (CPA) This can lead to so-called self-focusing, where the does, so the high-frequency component lags technique invented 25 years ago by Gérard intensity of the beam increases rapidly damaging behind the low-frequency component and the Mourou, now director of the Institut de la Lumière the optics in the process. pulse spreads out in time. Extrême at the Ecole Nationale Supérieure de To keep the intensity of laser pulses below the As the pulse is longer, its power is lower and its Techniques Avancées in France. threshold of nonlinear effects, laser systems had energy can then easily be increased by passing the To generate the high-energy beams, a standard to be very large and expensive, and the peak power pulse through a amplifier such as a titanium– off-the-shelf table-top laser source will be used to of laser pulses was still limited to a few terawatts sapphire crystal. The amplified pulse is then generate pulses that are a femtosecond in length. for very large multibeam facilities. In 1985 passed through a second pair of gratings that These pulses, however, only have a small amount Mourou, then at Rochester University, US, and reverse the dispersion – forcing the high-frequency of energy – about a nanojoule. To get a high- his colleague Donna Strickland, developed component of the laser pulse to travel a shorter powered petawatt beam, the energy needs to be CPA to get around the nonlinear effects (Optics path and the low-frequency component to travel a increased by a factor of about 1012. However, as Communications 56 219). It works by taking the longer path, so the pulse then “recombines” into a the energy of a short-pulse laser beam is short pulse and passing it through a pair of short femtosecond pulse.

12 Physics World May 2010 physicsworld.com News & Analysis accelerator. As the laser propagates Hegelich, project leader of short- through the plasma, the electrons are pulse experiments and lasers at the expelled around the laser pulse – just Los Alamos National Laboratory in as a boat displaces water around it as New Mexico, says there are some new it moves forward. As the electrons theories being proposed that could then rush back in behind the laser bring the Schwinger limit within ELI’s pulse, they set up a trailing wave-like reach. “The vacuum has energy levels structure known as a “wakefield” – and it would be great if we could like a water wave travelling behind CNRS Photothèque/Alexis Cheziere somehow manage to modify them,” the boat. Other plasma electrons says Hegelich. Mourou also say the trapped by these waves “surf” on Schwinger limit could be matched by them behind the laser pulse picking colliding electron beams created by up energy and accelerating. two lasers. This technique allows laser light One of the technical challenges of to accelerate electrons over a much the ultrahigh-peak-power facility will smaller distance than conventional south of Budapest, will generate pulses Particle test-bed be producing the vacuum itself. “Even particle accelerators, which can be every 1 ms that will be used to take The LASERIX laser ultrahigh-vacuum environments pro- tens of kilometres long. “Typically, we snap-shots on the attosecond scale at the Université duced by highly efficient pumps still think we can achieve electron ener- (10–18 s) of electron dynamics in atoms, Paris-Sud II has been have a few atoms floating around,” gies of about 10–20 GeV,” says Mou- plasmas and solids. It will do this by testing whether lasers says Hegelich. One method would be rou. “So instead of building a 1 km shooting a femtosecond pulse of light can produce X-rays, to first shoot a laser pulse into the linear accelerator, we can instead use at a dense plasma target. In a process as the Czech ELI high-vacuum environment that would something that is only 1 m long.” known as “relativistic harmonic gen- facility hopes to do. expel all the particles and then quickly Mourou says that the Prague ELI eration”, the ionized plasma then gives follow that up with a second high- centre, which could also accelerate off so-called phase-locked radiation in powered pulse. “Technically, there is protons for use in hadron therapy, the ultraviolet and soft X-ray regime nothing that can’t be overcome with will complement, rather than replace, at multiples of the frequency of the the ultrahigh-peak-power facility,” other facilities that generate short original femtosecond pulse. Research- says Hegelich. “It is more an engin- pulses of X-rays, such as the Linac ers at ELI will then select the pulses eering challenge that a physics one.” Coherent Light Source (LCLS) at the that are generated in the attosecond One phenomenon that ELI should SLAC National Accelerator Laborat - regime with a filter and send them to be able to detect, which is predicted ory. But while LCLS, which is an X-ray experimental stations to study mater- to happen at about 1023 Wcm–2, is the free-electron laser, can only produce ials on the atomic scale. vacuum becoming polarized and ex- monochromic radiation with pulse hibiting optical phenomenon such durations of the order of 100 fs, ELI Boiling the vacuum as birefringence. Some theorists are could produce polychromatic radi - The host for what is dubbed the already proposing experiments for the ation of the order of a femtosecond or “heart” of ELI – the “ultrahigh peak ultrahigh-peak-power facility such as less, making it possible to take images power” facility – will not be known a “matterless” double-slit experiment of chemical reactions in real time. until 2012, after some initial testing where the photons generated from “ELI is pushing the boundaries in of technology for the three main fa- electron and positron pairs annihil - terms of testing this technology to cilities is carried out. With an ex - ating form a double-slit diffraction provide a range of applications,” says pected completion date of 2018, the pattern (Nature Physics 4 92). John Collier, head of the high-power- facility will attempt to generate a As well as being a revolutionary lasers division at the Central Laser 100–200PW beam and use mirrors to physics project that will test funda- Facility at the Rutherford lab. focus it onto an area of 1 µm2 in the mental theories and show how lasers hope of ripping open the fabric of the could become the next particle accel- Ripping atoms vacuum to produce particle and anti- erator or collider, ELI is also tipping ELI’s nuclear-physics facility in Ro- particle pairs. “The vacuum is not the scales of Europe’s portfolio of mania is set to be built in Magu rele, something empty, but is full of activity major infrastructures slightly more 20 km south of Bucharest. The facil- of particles being created and de- eastwards. The presence of three ity will produce 10 PW beams that are stroyed,” says Mourou. “It defines all major facilities in the Czech Repub- shone directly onto a nucleus to study the constants of physics.” lic, Hungary and Romania will allow how the pulse affects nuclear energy Quantum field theory states these these nations to attract researchers levels. Researchers expect that the “virtual particles” continually pop in from abroad, as well as inspiring fu- laser pulse should be able to deposit and out of existence. It is predicted ture generations of researchers. about 1–10 keV on the nucleus – that paired virtual particles could be - “ELI will create new scientific com- enough to modify energy levels and come real as they are torn apart by munities and it will be a magnet for forcing it to release a gamma ray. De- the pulse’s extremely strong electro- hi-tech companies,” says Sander, who tecting this radiation would be proof magnetic fields. However, this hap- notes that for every euro spent on a that researchers have affected the pens too quickly to leave a trace and ELI will create large infrastructure, 74 is given back nucleus directly with laser light, thus requires light with an in tensity of to the economy. Yet for most physi- allowing them to study nuclear trans- about 1029 Wcm–2. Known as the new scientific cists, it is ELI’s ultrahigh-power facil- itions in more detail. “Schwinger limit”, it is seven orders of communities ity, which will provide laser power far As for the Hungarian “attosecond” magnitude larger than any current and it will beyond any existing today, that is the facility, it will use a 5 fs pulse with a laser can achieve. be a magnet most exciting and eagerly awaited. laser beam of a few joules to generate In its current design, ELI’s high- “Within the next decade,” says Mou- powers of the order of a petawatt. The intensity facility will only be able to for hi-tech rou, “we will be en tering a new para- facility, to be built in Szeged, 100 km reach 1025 Wcm2; however, Mannuel companies digm in physics.” 13 Physics World May 2010 physicsworld.com

Comments from physicsworld.com Usually, the “most commented” articles on High winds knocking down power lines is what’s Feedback physicsworld.com are those that concern causing mayhem on our grid, not wind generators controversial science policies, rather than or nuclear plants. Bring on the undersea bags! Letters to the Editor can be sent to Physics World, science itself. Now and then, though, a scientific dratman, US Dirac House, Temple Back, Bristol BS1 6BE, UK, story – in this case a proposed method for or to [email protected]. Please include your address and storing wind energy in giant undersea bags – The bag might be a problem. I propose a simpler a telephone number. Letters should be no more than captures readers’ imaginations (“Spin-out puts solution to store the air underwater: an open-ended 500 words and may be edited. Comments on articles new spin on wind energy” 30 March; see also can or concrete caisson, sealed at the top and from physicsworld.com can be posted on the website; p8). The idea would see pistons inside the blades open at the bottom. No moving parts. an edited selection appears here of giant wind turbines used to pump compressed AlanM air into storage balloons; on calm days, the stored air could be released to drive a set Wouldn’t it be a lot easier to pump water up a hill? of turbines, thus ensuring a continuous supply John Duffield, UK Eensey, weensey units of electricity. According to inventor You reported last month (April p3) on the Seamus Garvey, a similar scheme could help Yes, pumping water uphill would work – but you efforts of Austin Sendek, a physics student store surplus energy from nuclear reactors. An have to have a hill, and preferably a high one. from the University of California, Davis, interesting notion, certainly – but is there a I think an air-pump system would be more to establish the “hella” as an official catch somewhere? maintenance-free than a pumping system that has International System of Units (SI) prefix to deal with the corrosive effects of salt water. for 1027. You also asked for suggestions on The proposal to use a bag system for storing Newbeak unit prefixes that go down to 10–27 – but “surplus energy from nuclear reactors” sounds surely this is not difficult. I have long funny. It’s designed to store energy from unreliable Is the weight of the piston inside the vanes the only declared the “tini” (pronounced with an sources, so I’d stick to that – it’s wind generators thing supplying force to pump the air down to “ee” sound) to denote this quantity. This that are causing mayhem on our energy grid, not 500 m below sea level? designation has the additional value of nuclear plants. feet2thefire suggesting the subsequent two prefixes as kasuha, Czech Republic well: the “insi” (pronounced “eensey”) for I get a pressure of about 710 psi at 500 m. You 10–30, to be followed closely by the “winsi” I agree that you should confine this system to wind, could have a piston with a cross-section of (pronounced “weensey”). but I disagree that wind is causing havoc on the 0.1 square inches (just under 3/16 inch radius) I have tried to think of prefixes that grid. We also need to look at the environmental weighing 71 lb. If the weight of the piston were the would come in on the high end beyond impacts, which will be significant if we start only drive, it would need to be prohibitively long, “hella” but unfortunately I could think of installing thousands of floating airbags at the possibly over 65 m if it were made of steel. So nothing that could not be interpreted as a bottom of the ocean. But then again, nothing is probably the plan would include some kind of rude word. Maybe I should not have worse than coal and gas. weight behind the piston. But the rotating parts limited myself to the English language. gunslingor, US would still need to seal against approximately B Todd Huffman 710 psi, which is 49 atmospheres. This seems to University of Oxford, UK You probably haven’t had enough blackouts me to be the killer for the engineering end of it. [email protected] caused by wind turbines overloading the grid yet. m.a.king, Canada Environmental or not (and I think these bags are far We already have the prefix “zepto” for from environmentally friendly – they are going to 10–21, but this is clearly a mistake for damage quite large areas of sea bed), wind “zeppo”. Could we not have groucho, turbines are causing many problems and chico and harpo as prefixes for 10–27, 10–30 desperately need reliable means of energy storage. Read these comments in full and add your own at and 10–33? kasuha physicsworld.com Keith Doyle Walton on Thames, Surrey, UK [email protected] suggested “sansa” for 1030 (san-shi being Using Mayes’ prefixes, the power of the Chinese for “thirty”); “besa” for 1033 (besar Sun can be written as 0.38 navawatt, There is no need for a new “hella” prefix, as means “great” in Malay-Indonesian) and while the mass of the galaxy is about an extended set of SI prefixes has already so on up to “ultra” (Latin for “beyond, 220 catagrams (from the Spanish catorce or been suggested by Victor Mayes. Writing in extreme”) for 1048. In a similar vein, Mayes’ “fourteen”, denoting 1042 = 100014) and 1994 in the Quarterly Journal of the Royal system assigned “tiso” (Arabic tis’a or the electron rest mass is 0.91 tisogram. Astronomical Society (35 569) Mayes’ “nine”) to 10–27; “vindo” (from Hindi J Keith Atkin suggestion for 1027 was “nava”, from the vindu, “a speck”) to 10–30 and “weto” University of Sheffield, UK Sanskrit for nine (1027 = 10009). He also (Maori wheto, “small”) to 10–33. [email protected]

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Subscription information 2010 volume The subscription rates for institutions are £310/7460/$585 per annum. Single issues are Let there be light £25.00/736.00/$47.00. Orders to: IOP Circulation Centre, Optima Data Intelligence Ltd, 12/13 Cranleigh This issue of Physics World celebrates the 50th anniversary of the invention of the laser Gardens Industrial Estate, Southall, Middlesex UB1 2DB, UK (tel: +44 (0)845 4561511; fax: +44 (0)870 4420055; When Theodore Maiman eked out the first pulses of coherent light from a pink- e-mail: [email protected]). Physics World is available ruby crystal on 16 May 1960, the 32-year-old engineer-turned-physicist at Hughes on an individual basis, worldwide, through membership of the Institute of Physics Research Laboratories in the US could not have imagined that the laser would become such a workhorse of physics – and so engrained in everyday life. Within Copyright © 2010 by IOP Publishing Ltd and individual contributors. All rights reserved. IOP Publishing Ltd permits weeks, other physicists – notably those at Bell Laboratories – had reproduced single photocopying of single articles for private study or Maiman’s success, with Bell Labs scientists then quickly notching up many other research, irrespective of where the copying is done. laser “firsts”, including the first gas lasers and the first continuously operating Multiple copying of contents or parts thereof without permission is in breach of copyright, except in the UK ruby lasers. under the terms of the agreement between the CVCP and Lasers have gone on to be one of the outstanding success stories in physics. They the CLA. Authorization of photocopy items for internal or personal use, or the internal or personal use of specific can cool atoms, send data, mend eyes, sharpen astronomical images and probe clients, is granted by IOP Publishing Ltd for libraries and individual DNA molecules; they may even detect gravitational waves and trigger other users registered with the Copyright Clearance Center (CCC) Transactional Reporting Service, provided that fusion. Hardly surprising then that, by our reckoning, some 14 physics Nobel prizes the base fee of $2.50 per copy is paid directly to have been awarded for achievements directly related – or linked – to lasers. Indeed, CCC, 27 Congress Street, Salem, MA 01970, USA despite their use in the military, lasers do not suffer from an image problem, being Bibliographic codes ISSN: 0953-8585 widely regarded as a “good thing”. CODEN: PHWOEW This special issue of Physics World kicks off by reliving the laser’s first days and by Printed in the UK by Warners (Midlands) plc, The Maltings, West Street, Bourne, Lincolnshire PE10 9PH celebrating its impact on popular culture (think Goldfinger and laser-art shows) and everyday life (DVDs, laser pointers, bar-code scanners). We look at the tech- nological impact of lasers in fibre optics and at the quest for green-wavelength laser diodes that could let mobile phones project images onto any surface. Basic The Institute of Physics research gets a look-in, too – in terms of both ultrahigh power and ultrafast lasers. 76 Portland Place, London W1B 1NT, UK Tel: +44 (0)20 7470 4800 There is a timeline of laser history, while six experts predict where laser science Fax: +44 (0)20 7470 4848 will go next. Online, don’t miss our video interviews with leading laser scientists, E-mail: [email protected] while the physicsworld.com blog reveals how we created our cover image and the Web: iop.org photo above. (As it turns out, there are some things lasers can’t do so well.) Matin Durrani, Editor of Physics World

The contents of this magazine, including the views expressed above, are the responsibility of the Editor. They do not represent the views or policies of the Institute of Physics, except where explicitly stated. 15 Physics World May 2010 The laser at 50: A cultural history physicsworld.com From ray-gun to Blu-ray The first public reactions to lasers ranged from “Death ray!” to “Nice idea, but what good is it?”. Sidney Perkowitz reviews how lasers are now inextricably entwined in our lives, from everyday applications to popular culture

Sidney Perkowitz There is one particular scene in H G Wells’ 1898 tale is Candler Professor The War of the Worlds that, if only I had remembered it, of Physics at Emory could have helped me to avoid a bad moment in my University, US, e-mail laser lab in 1980. In the story – published long before [email protected]. lasers came along in 1960 – the Martians wreak destruc- Also a science writer, tion on earthlings with a ray that the protagonist calls an his latest book – Hollywood Science: “invisible, inevitable sword of heat”, projected as if an Movies, Science and “intensely heated finger were drawn…between me and the End of the World – the Martians”. In all but name, Wells was describing an has just been infrared laser emitting an invisible straight-line beam – reissued in paperback the same type of laser that, decades later in my lab, by Columbia burned through a favourite shirt and started on my arm. University Press Wells’ bold prediction of a destructive beam weapon preceded many others in science fiction. From the 1920s and 1930s, Buck Rogers and Flash Gordon wielded eye-catching art-deco ray-guns in their space adventures as shown in comics and in films. In 1951 the powerful robot Gort projected a ray that neatly dis- posed of threatening weapons in the film The Day the Earth Stood Still. Such appearances established laser- like devices in the popular mind even before they were invented. But by the time the evil Empire in Star Wars Episode IV: A New Hope (1977) used its Death Star laser to destroy an entire planet, lasers were a thing of fact, not just fiction. Lasers were changing how we live, sometimes in ways so dramatic that one might ask, which is the truth and which the fiction? Like the fictional science, the real physics behind lasers has its own long history. One essential starting fornia, made it work. In 1960 he amplified red light point is 1917, when Einstein, following his brilliant suc- within a solid ruby rod to make the first laser. Its name cesses with relativity and the theory of the photon, was coined by Gordon Gould, a graduate student established the idea of stimulated emission, in which a working at Columbia University, who took the word photon induces an excited atom to emit an identical “maser” and replaced “microwave” with “light”, and photon. Almost four decades later, in the 1950s, the US later re ceived patent rights for his own contributions physicist Charles Townes used this phenomenon to to laser science. produce powerful microwaves from a molecular me- Following Maiman’s demonstration of the first laser dium held in a cavity. He summarized the basic process there was much excitement and enthusiasm in the field, – microwave amplification by stimulated emission of and the ruby laser was soon followed by the helium radiation – in the acronym “maser”. neon or HeNe laser, invented at Bell Laboratories in After Townes and his colleague Arthur Schawlow 1960. Capable of operating as a small, low-power unit, proposed a similar scheme for visible light, Theodore it produced a steady, bright-red emission at 633 nm. Maiman, of the Hughes Research Laboratories in Cali - However, an even handier type was discovered two 16 Physics World May 2010 physicsworld.com The laser at 50: A cultural history Danjaq/EON/UA/The Kobal Collection

years later when a research group at General Electric dismayed that his invention was immediately called a Do you expect me saw laser action from an electrical diode made of the “death ray” in a sensationalist newspaper headline, to talk? semiconductor gallium arsenide. That first laser diode lasers powerful enough to be used as weapons would James Bond is held has since mushroomed into a versatile family of small not be seen for another 20 years. Indeed, the most wide- captive by Goldfinger devices that covers a wide range of wavelengths and spread versions are compact units typically producing and his sci-fi red laser that can cut powers. The diode laser quickly became the most pre- mere milliwatts. through gold. valent type of laser, and still is to this day – according A decade and a half after their invention, HeNe to a recent market survey, 733 million of them were sold lasers, and then diode lasers, would become the basis in 2004. of bar-code scanning – the computerized registration of the black and white pattern that identifies a product Better living through lasers according to its universal product code (UPC). The As various types of laser became available, and different idea of automating such data for use in sales and inven- uses for them were developed, these devices entered tory originated in the 1930s, but it was not until 1974 our lives to an extraordinary extent. While Maiman was that the first in-service laser scanning of an item with a 17 Physics World May 2010 The laser at 50: A cultural history physicsworld.com Photolibrary TEK Image/Science Photo Library

UPC symbol – a pack of Wrigley’s chewing gum – though as usual, Bond emerges unscathed. occurred at a supermarket checkout counter in Ohio. That laser projected red light to add visual drama, Now used globally in dozens of industries, bar codes but its ability to cut metal foretold the invisible infrared are scanned billions of times daily and are claimed to beam of the powerful carbon-dioxide (CO2) laser – the save billions of dollars a year for consumers, retailers type that once ruined my shirt. Invented in 1964, CO2 and manufacturers alike. lasers emitting hundreds of watts in continuous opera - Lasers would also come to dominate the way in which tion were introduced as industrial cutting tools in the we communicate. They now connect many millions of 1970s. Now, kilowatt versions are available for uses computers around the world by flashing binary bits into such as “remote welding” in the automobile industry, networks of pure-glass optical fibre at rates of terabytes where a laser beam directed by steerable optics can per second. Telephone companies began installing rapidly complete multiple metal spot welds. High- optical-fibre infrastructure in the late 1970s and the first power lasers are suitable for other varied industrial transatlantic fibre-optic cable began operating between tasks, and even for shelling nuts. the US and Europe in 1988, with tens of thousands of kilometres of undersea fibre-optic cabling now in ex- Digital media istence worldwide. This global web is activated by laser Aside from the helpful and practical uses of lasers, diodes, which deliver light into fibres with core diam- what have they done to entertain us? For one thing, eters of a few micrometres at wavelengths that are lasers can precisely control light waves, allowing sound barely attenuated over long distances. In this role, lasers waves to be recorded as tiny markings in digital format have become integral to our interconnected world. and the sound to be played back with great fidelity. In As lasers grew in importance, their fictional ver- the late 1970s, Sony and Philips began developing sions kept pace with – and even enhanced – the reality. music digitally encoded on shiny plastic “compact Only four years after the laser was invented, the film discs” (CDs) 12 cm in diameter. The digital bits were Goldfinger (1964) featured a memorable scene that represented by micrometre-sized pits etched into the had every man in the audience squirming: Sean Con - plastic and scanned for playback by a laser diode in a nery as James Bond is tied to a solid gold table along CD player. In retrospect, this new technology deserved which a laser beam moves, vaporizing the gold in its to be launched with its own musical fanfare, but the path and heading inexorably toward Bond’s crotch – first CD released, in 1982, was the commercial album 52nd Street by rock artist Billy Joel. In the mid-1990s the CD’s capacity of 74 minutes of Lasers would come to dominate the music was greatly extended via digital versatile discs or digital video discs (DVDs) that can hold an entire way in which we communicate. feature-length film. In 2009 Blu-ray discs (BDs) ap- peared as a new standard that can hold up to 50 giga- They now connect many millions of bytes, which is sufficient to store a film at exceptionally high resolution. The difference between these formats is the laser wavelengths used to write and read them – computers around the world by 780 nm for CDs, 650 nm for DVDs and 405 nm for BDs. The shorter wavelengths give smaller diffraction- flashing binary bits into networks limited laser spots, which allow more data to be fitted into a given space. of pure-glass optical fibre at rates of Although the download revolution has led to a de- cline in CD sales – 27% of music revenue last year was terabytes per second from digital downloads – lasers remain essential to our 18 Physics World May 2010 physicsworld.com The laser at 50: A cultural history GIPhotoStock/Science Photo Library NIH/Custom Medical Stock Photo/Science Photo Library

entertainment. They carry music, films and everything ably science-fiction flavour. But the US weaponization Make light work that streams over or can be downloaded via the Inter- of space was never realized – by the 1990s technical dif- The diverse uses of net and telecoms channels, depositing them into our ficulties and the fall of the Soviet Union had turned lasers include (left computers, smart phones and other digital devices. laser-weapons development elsewhere. Now it is mostly to right) bar-code directed towards smaller weapons such as airborne scanning, transmitting Death rays... lasers that have a range of hundreds of kilometres. information via optical fibres, Blu-ray discs Among the films that you might choose to download and laser eye surgery. over the Internet are some in which lasers are por- ...and life rays trayed as destructive devices, encouraging negative While the morality associated with weapons may be connotations. In the film Real Genius (1985), a scien- debatable, lasers are used in many other areas that are tist co-opts two brilliant young students to develop an undeniably good, such as medicine. The first medical airborne laser assassination weapon for the military use of a laser was in 1961, when doctors at Columbia and the CIA. The students avenge themselves by sabo- University Medical Center in New York destroyed a taging the laser to heat a huge vat of popcorn, produ- tumour on a patient’s retina with a ruby laser. Because cing a tsunami of popped kernels that bursts open a laser beam can enter the eye without injury, ophthal- the scientist’s house. The film RoboCop (1987) shows mology has benefited in particular from laser methods, a news report that a malfunctioning US laser in orbit but their versatility has also led to laser diagnosis and around the Earth has wiped out part of Southern treatment in other medical areas. California. This was a satirical response to the idea of Using CO2 and other types of lasers with varied wave- laser weapons in space, a hotly pursued dream for then lengths, power levels and pulse rates, doctors can pre- US President Ronald Reagan. cisely vaporize tissue, and can also cut tissue while The US military was thinking about laser weapons simultaneously cauterizing it to reduce surgical trauma. well before high-power industrial CO2 lasers were melt- One example of medical use is LASIK (laser-assisted ing metal. As the Cold War raised fears of all-out con- in situ keratomileusis) surgery in which a laser beam flict with the Soviet Union, the potential for a new reshapes the cornea to correct faulty vision. By 2007, hi-tech weapon stimulated the Pentagon to fund laser some 17 million people worldwide had undergone research even before Maiman’s result. But it was dif - the procedure. ficult to generate enough beam power within a rea- In dermatology, lasers are routinely used to treat sonably sized device – early CO2 lasers with kilowatt benign and malignant skin tumours, and also to pro- outputs were too unwieldy for the battlefield. Even- vide cosmetic improvements such as removing birth- tually, in 1980, the Mid-Infrared Advanced Chemical marks or unwanted tattoos. Other medical uses are as Laser reached pulsed powers of megawatts, but was still diverse as treating inaccessible brain tumours with laser a massive device. Even worse, absorption and other light guided by a fibre-optic cable, reconstructing dam- atmospheric effects made its beam ineffective by the aged or obstructed fallopian tubes and treating her- time it reached its target. niated discs to relieve lower-back pain, a procedure That would not be a concern, however, for lasers fired carried out on 500 000 patients per year in the US. in space to destroy nuclear-tipped intercontinental Yet another noble aim of using lasers is in basic and ballistic missiles (ICBMs) before they re-entered the applied research. One notable example is the National atmosphere. Development of suitably powerful lasers Ignition Facility (NIF) at the Lawrence Livermore Na- such as those emitting X-rays became part of the multi- tional Laboratory in California. NIF’s 192 ultraviolet billion-dollar anti-ICBM Strategic Defense Initiative laser beams, housed in a stadium-sized, 10-storey (SDI) proposed by Reagan in 1983. Known to the gen- building, are designed to deliver a brief laser pulse eral public and even to scientists and the government as measured in hundreds of terawatts into a millimetre- “Star Wars” after the film, the scheme had an undeni- scale, deutrium-filled pellet. This is expected to create 19 Physics World May 2010 The laser at 50: A cultural history physicsworld.com

iums. A favourite type featured “space” music, like that from Star Wars, accompanied by laser effects. Rock concerts by Pink Floyd and other groups were Hiro Yamagata also known for their laser shows, though these are now tightly regulated because of safety issues. But spec - tacular works of laser art continue to be mounted, for example the outdoor installations “Photon 999” (2001) and “Quantum Field X3” (2004) created at the Gug- genheim Museum in Bilbao, Spain, by Japanese-born artist Hiro Yamagata, and the collaborative Hope Street Project, installed in 2008. This linked together two major cathedrals in Liverpool, UK, by intense laser beams – one highly visible green beam and also several invisible ones – that carried voices and generated ambi- ent music to be heard at both sites. After 50 years, striking laser displays can still evoke awe, and lasers still carry a science-fiction-ish aura, as demonstrated by hobbyists who fashion mock ray-guns from blue laser diodes. Unfortunately, the mystique See the light conditions like those inside a star or a nuclear explo - also attaches itself to products such as the so-called Artist Hiro Yamagata sion, allowing the study of both astrophysical processes quantum healing cold laser, whose grandiose title uses linked science and nuclear weapons. scientific jargon to impress would-be customers. Its with art at his A more widely publicized goal is to induce the hy- maker, Scalar Wave Lasers, asserts that its 16 red and “Photon 999” drogen nuclei to fuse into helium, as happens inside infrared laser diodes provide substantial health and exhibition, where the Sun, to produce an enormous energy output. After rejuvenation benefits. Even the word “laser” has been multiple laser some 60 years of effort using varied approaches, scien- appropriated to suggest speed or power, such as for the systems immersed the viewers in a tists have yet to achieve fusion power that produces popular Laser class of small sailboats and the Chrysler moving-light show. more energy than a power plant would need to operate. and Plymouth Laser sports cars sold from the mid- If laser fusion were to successfully provide this limitless, 1980s to the early 1990s. non-polluting energy source, that would more than The laser’s distinctive properties have also become justify the overruns that have brought the cost of NIF enshrined in language. A search of the massive Lexis- to $3.5bn. Although some critics consider laser fusion Nexis Academic research database (which encompasses a long shot, recent work at NIF has realized some of its thousands of newspapers, wire services, broadcast tran- initial steps, increasing the odds for successful fusion. scripts and other sources) covering the last two years Popular culture is also hopeful about the role of lasers yields nearly 400 references to phrases such as “laser- in “green” power. Although the film Chain Reaction like focus” (appearing often enough to be a cliché), (1996) badly scrambles the science, it does show a “laser-like precision”, “laser-like clarity” and, in a des- laser releasing vast amounts of clean energy from the cription of Russian Prime Minister Vladimir Putin ex - hydrogen in water. In Spider-Man 2 (2004), physicist pressing his displeasure with a particular businessman, Dr Octavius uses lasers to initiate hydrogen fusion that “laser-like stare”. will supposedly help humanity; unfortunately, this is Lasers have significantly influenced both daily life no advertisement for the benefits of fusion power, for and science. With masers, they have been part of re- the reaction runs wild and destroys his lab. search, including work outside laser science itself, that has contributed to more than 10 Nobel prizes, begin- Lasers in high and not-so-high culture ning with the 1964 physics prize awarded to Charles Situated between the ultra-powerful lasers meant to Townes with Alexsandr Prokhorov and Nicolay Basov excite fusion and the low-power units at checkout coun- for their fundamental work on lasers. Other related ters are lasers with mid-range powers that can provide Nobel-prize research includes the invention of holog- highly visible applications in art and entertainment, as raphy and the creation of the first Bose– Einstein con- artists quickly realized. A major exhibit of laser art was densate, which was made by laser cooling a cloud of held at the Cincinnati Museum of Art as early as 1969, atoms to ultra-low temperatures. Also, in dozens of and in 1971 a sculpture made of laser beams was part applications from Raman spectroscopy to adaptive of the noted “Art and Technology” show at the Los An - optics for astronomical telescopes, lasers continually geles County Museum of Art. In 1970 the well-known contribute to how science is done. They are also essen- US artist Bruce Nauman presented “Making Faces”, a tial for research in such emerging fields as quantum series of laser hologram self-portraits, at New York entanglement and slow light. City’s Finch College Museum of Art. It is a tribute to the scientific imagination of the laser Other artists followed suit in galleries and museums, pioneers, as well as to the literary imagination of wri- but lasers have been most evident in larger venues. ters such as H G Wells, that an old science-fiction idea Beginning in the late 1960s, beam-scanning systems has come so fully to life. But not even imaginative wri- were invented that allowed laser beams to dynamically ters foresaw that Maiman’s invention would change the follow music and trace intricate patterns in space. This music business, create glowing art and operate in su- led to spectacular shows such as that at the Expo ’70 per markets across the globe. In the cultural impact of World’s Fair in Osaka, Japan, and those in planetar - the laser, at least, truth really does outdo fiction. 20 Physics World May 2010 XRF Solutions • Solid State Design • No Liquid Nitrogen!! • Thermoelectric Cooler • Easy to Use • USB Controlled • Low Cost

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Untitled-9 1 17/11/09 11:30:16 CCDec09AdLaserSupport.indd 1 17/11/09 12:47:50 physicsworld.com The laser at 50: The early years Theodore Harold Maiman

And then there was light The laser’s early years were full of scientific creativity, public-relations spin and intense rivalry. Pauline Rigby describes how a then little-known scientist became the first person to design and build a working laser – and how the competitiveness of that period persists to this day

The race to make a laser began with Bell Laboratories. – an acronym for microwave amplification by stimu- In the late 1950s the then Bell Telephone Laboratories lated emission of radiation. And in December 1958, was a well-funded research institute in Murray Hill, Townes and his brother-in-law Arthur Schawlow wrote New Jersey, that already had a string of high-profile a famous paper (Physical Review 112 1940) describing achievements to its name – including the transistor, how the maser concept could be extended into the which was invented in 1947 by John Bardeen, Walter optical regime, to make the first “infrared and optical Brattain and William Shockley. A few years later, a maser” – in other words, a laser. Pauline Rigby is a Bell Labs re search group led by Charles Townes pro- So if there was going to be a race to build a laser, it freelance technology posed a device that could produce and amplify elec- was a race that Bell Labs fully expected to win. But the writer based in the tromagnetic radiation in the microwave region of the favourites quickly faced competition. Townes had been Cotswolds, UK, spectrum. By 1953 the researchers had turned their consulting at Bell Labs, but by the time his 1958 paper e-mail pauline@ theory into a working device, which they called a maser was published he was back at Columbia University. opticalreflection.com 23 Physics World May 2010 The laser at 50: The early years physicsworld.com

First light: key dates in the invention of the laser so he could pursue his ideas. The company won a $1m grant from the defence-related Advanced Research 15 December 1958 Arthur Schawlow and Charles Townes’ paper on “Infrared and Projects Agency to work on the laser, but Gould was optical masers” appears (Phys. Rev. 112 1940) barred from taking part in the project because it was 15 July 1959 Ali Javan publishes his proposal for making a gas laser (Phys. Rev. Lett. classified and he could not get security clearance. 3 87) 16 May 1960 Theodore Maiman observes pulsed lasing in pink ruby Late entry 7 July 1960 Hughes Research Laboratories holds a press conference announcing The dark horse in the race was Theodore Harold Mai- Maiman’s laser man, who was then at Hughes Research Laboratories, 20 July 1960 Maiman improves his ruby laser design and observes a pencil beam the research arm of the Hughes Aircraft Company. 1 August 1960 Donald Nelson and colleagues at Bell Labs create a pulsed laser Maiman was an engineer by training who had switched beam from a ruby rod in a configuration similar to the one shown in press to physics, studying the fine-structure splittings of photographs of Maiman’s device energy levels in excited helium atoms at Stanford 6 August 1960 Maiman’s short letter “Stimulated optical radiation in ruby” is University under Willis Lamb, who had won the 1955 published (Nature 187 493) Nobel Prize for Physics. In the quest to make a laser, 25 September 1960 Nelson and his team at Bell Labs flash a laser beam 25 miles Maiman’s engineering and physics experience would from Crawford Hill to Murray Hill in New Jersey both prove essential. 1 October 1960 Publication of Bell Labs’ ruby-laser paper (Phys. Rev. Lett. 5 303) Maiman entered the race late, at the point when 5 October 1960 Bell Labs holds a press conference to announce its ruby laser many researchers appeared to be on the point of giv- 12 December 1960 Javan and his team create the first gas laser ing up. Moreover, Hughes took some persuading to 30 January 1961 Javan’s paper on the gas laser appears (Phys. Rev. Lett. 6 106) fund his interest in lasers. After all, it was in the aero- 31 January 1961 Bell Labs holds a press conference announcing the gas laser space business. What would it do with a beam of light? 1961 Willard Boyle and Nelson create the first continuously operating ruby laser However, Hughes did have a contract with the US (Appl. Opt. 1 181) Army Corps of Engineers to make a maser. This turned out to be Maiman’s opportunity. “Ted struck an agreement with Hughes,” Maiman’s There, he began trying to make a laser using hot potas- wife Kathleen recalled during an interview with sium vapour – the medium described in the paper. Physics World (Maiman died in 2007, aged 79). “If he Schawlow decided not to go into direct competition was successful in delivering the maser for the Army with Townes, and so selected ruby as an alternative Corps of Engin eers, he would be given nine months potential laser material, in part because Bell Labs had and $50 000 to actually make coherent light. He went a good supply of synthetic rubies for maser research. A to work to make the maser more practical, and took it second Bell Labs team was studying visible emissions from 5000 lbs to 2.5 lbs and also improved the line- from calcium-fluoride crystals doped with various rare- width. Because of that, he was able to do a dedicated earth metals; a third, led by Townes’ former graduate project on the laser.” student Ali Javan, was trying to build a gas laser using Like Schawlow, Maiman started investigating ruby helium and neon. as a laser material because he was familiar with its prop- Beyond Bell Labs, other research institutes around erties from his maser work. Ruby is a crystal of alu- the world soon joined the race. In the US alone, there minium oxide containing a tiny amount of chromium were major research efforts going on at General Elec - – about 0.5% in the case of gemstone ruby, and about a tric, IBM, the Massachusetts Institute of Techno logy’s 10th of that in “pink” ruby used for industrial appli- Lincoln Laboratory, RCA Labor at ories and West - cations. As well as emitting microwaves, pink ruby also inghouse Research. Another strong contender was strongly absorbs light in the green part of the optical Townes’ former student Gordon Gould, who had inde- spectrum, and fluoresces in the red. Such behaviour is pendently come up with an idea for a sodium-vapour- a consequence of pink ruby’s three-level energy system based device in 1957 – coining the term “laser” in the (figure 1). When pink ruby absorbs green light, elec- process. The following year Gould abandoned his PhD trons are promoted from the ground state to a higher thesis and joined TRG, a private research company, energy level. The electrons then lose energy through thermal relaxation (lattice vibrations), ending up in an intermediate, metastable energy level. Decay from this The dark horse in the laser race was metastable level back to the ground state is responsible for the red fluorescence, and this was the transition Theodore Harold Maiman, an Maiman hoped to use in his laser. But in September 1959, shortly after Maiman started engineer by training who had his project, Schawlow publicly declared that pink ruby could not possibly work as a laser. For stimulated emis- sion to occur, more electrons need to reside in the up- switched to physics. In the quest to per energy level than a lower one – a condition known as a population inversion. Schawlow argued that it make a laser, Maiman’s engineering would be too difficult to achieve this inversion in a three-level system because the ground state in such a and physics experience would system is usually full of electrons. He maintained that it would be much easier to achieve population inver- both prove essential sion in a four-level system containing an empty energy 24 Physics World May 2010 physicsworld.com The laser at 50: The early years

1 A three-level system in pink ruby 2 Three- and four-level laser systems short-lived fast decay excited states thermal metastable relaxation short-lived fast decay lasing transition metastable short-lived

pumping light metastable levels pump lasing transition pump fast decay laser transition 694.3 nm ground state ground state In a three-level laser system, more than half of the particles in the laser medium must be pumped out of the ground state and into the metastable state (via the short-lived excited state) for a population inversion to occur. Achieving this requires a very intense pumping light. ground state Population inversion in a four-level laser system, in contrast, occurs whenever the population of Chromium ions in pink ruby absorb light in the green and blue regions the metastable state exceeds that of the lower short-lived state. Hence, only a few particles of the spectrum. In the presence of this pumping light, electrons in the need to be excited before stimulated emission can take place. ions are promoted to excited states, where they then rapidly decay to one of two metastable levels. The unusually long lifetime (about 4 ms) is about 5500 K.) This was a departure from the of these levels allows more than half of the available electrons to build methods of other researchers, who were working with up there, creating a population inversion – the condition needed for continuous illumination. lasing to occur. The next problem was how to concentrate the light onto the ruby. According to Maiman’s calculations, level between the ground state and the meta stable lamps shaped like straight tubes – which could be posi- level (figure 2). tioned at the focus of an elliptical mirror – would not With respected scientists counselling against pink be powerful enough. The most powerful strobe lamps ruby, Maiman’s employer was reluctant to continue of the time had a spiral shape, and so he decided to funding his idea, which it was doing out of its own “stick with what was available”. The spiral shape of the pocket. But Maiman was not deterred, because it was lamp meant he could not use a simple lens to focus the clear from Schawlow’s comments that he was consid- light onto the ruby crystal, so Maiman positioned the ering a cryogenically cooled laser. As Maiman wrote in ruby as close to the light source as possible. This meant his memoirs, The Laser Odyssey (2000 Laser Press), putting the 1 × 2 cm ruby inside the lamp spiral, and “the possibility of room-temperature operation had placing the entire arrangement inside a polished alu- been dismissed out of hand”. minium cylinder to help gather the light (see image on Maiman’s only moment of real doubt came when a page 23). Thick silver coatings on the ends of the ruby scientist he had personally trained, Irwin Wieder, pub- were used to create the optical cavity, leaving a small lished a paper claiming that the quantum efficiency of hole in the coating at one end to allow light to escape. ruby fluorescence was just 1% – in other words, only On 16 May 1960 his work paid off. Maiman and his one absorbed photon in 100 results in an emitted pho- assistant Irnee d’Haenens observed the first evidence ton (Review Scientific Instruments 30 995). If true, this of laser action: a large decrease in the ruby’s fluor- would mean it would be impossible to pump enough escence lifetime as seen in the device’s spectral output, energy into ruby to achieve stimulated emission. But once the flash-lamp input was increased to more than instead of giving up, Maiman devised experiments to 950 V. Below this threshold, the only light-emission determine why the quantum efficiency of ruby fluor- mechanism is normal fluorescence. Above it, however, escence should be so low, in order to guide his search stimulated emission becomes the dominant process, for a suitable alternative. Finding no answers, in the end and the metastable energy level empties much faster, he made his own measurements on ruby, which showed leading to a reduction in the fluorescence lifetime. that the quantum efficiency was actually closer to 75%. In a second experiment performed a few days later, This was typical of Maiman’s approach to research, Maiman used a spectrograph to measure narrowing in according to Kathleen. “Ted was a very, very careful spectral linewidth above the laser threshold – another scientist, and very precise in his work,” she says. “He characteristic of stimulated emission. Furthermore, didn’t take anything at face value. He calculated and pink ruby’s red fluorescence consists of two closely recalculated until he was absolutely sure it was correct.” spaced spectral lines, and Maiman had calculated that Even with 75% quantum efficiency, Maiman’s calcu- only one of these lines would actually lase – and that is lations indicated that he would need a very bright pump exactly what he saw. light to deliver enough energy to the pink ruby to achieve stimulated emission. His “eureka” moment Into the limelight came from reading an article about photographic Having fought to obtain funding to carry out his re - strobe lamps, which could achieve “brightness tem - search in the first place, Maiman then faced an uphill peratures” of 8000 K, albeit only for a moment. (Bright - struggle to get his discovery acknowledged. When he ness temperature is a measure of radiation intensity submitted a paper to Physical Review Letters, it was re - in terms of the temperature of a hypothetical black jected as “just another maser paper”. Maiman quickly body. For reference, the Sun’s brightness temperature penned a shorter, 300-word version of his article and 25 Physics World May 2010 The laser at 50: The early years physicsworld.com

from an unknown working for an aircraft company. The biggest problem, however, was that Mai man’s detailed scientific results were not available for scrutiny when the press conference was held. Worse, the Nature paper – when it was finally published on 6 August – was so brief that it failed to convince his critics. Despite the uncertainty, Hughes’ press conference Hughes Research Laboratories infused the laser research community with new vigour and new funding. Scientists around the world returned to their work with fresh conviction that it was actually possible to make a laser. In fact, the concept and design of Maiman’s laser proved so simple that it was only a matter of weeks before his results had been reproduced by several other researchers – most prominently those at Bell Labs, who demonstrated a pencil beam from their ruby device on 1 August 1960. Taking their cue from the publicity photograph showing “not the first” laser (see image left), the Bell Labs researchers used a 5 cm-long ruby rod with an identical model of strobe lamp. By then, Maiman had also observed a pencil beam, thanks to three new ruby crystals that had been spe- cially grown to the dimensions he required (the ruby in the first laser, by contrast, had been cut from a larger boule). On the day the new crystals arrived, 20 July 1960, Maiman inserted them into his device and observed sharp threshold behaviour and a bright spot on the wall.

Still controversial In the years that followed, Bell Labs researchers achieved many laser “firsts”, including the first gas laser, which Javan and co-workers demonstrated suc- cessfully in December 1960. Other successes included the first continuously operating ruby laser, made by Willard Boyle and Donald Nelson in 1961; the first car- Better than the sent it to Nature, where it was accepted (187 493). Be- bon-dioxide laser, invented by Kumar Patel in 1964; real thing? fore it could be published, however, Hughes decided to and a string of other innovations, including refinements The photograph hold a press conference. As a scientist, Maiman wanted to the now-ubiquitous semiconductor diode laser. issued at the 7 July to publish first, but Hughes was becoming nervous: the Maiman, for his part, left Hughes in 1961 to join a 1960 Hughes press Bell Labs groups might be really close, and there would venture-capital-funded start-up called Quanatron, conference showing be no prize for second place. where he was in charge of laser activities. The following Maiman with a later prototype laser – not The Hughes public-relations machine swung into year Union Carbide provided the funds to set up his lab the first one– led action ahead of the press conference, which it had as an independent business. Thus Maiman became to melodramatic scheduled for 7 July 1960. The photographer hired to president of the newly formed Korad Corporation, newspaper headlines take the shots was not impressed by the first laser – it which invented the Q-switched laser and became a sup- and confusion among was too small (see image on page 23). Looking around plier of the highest power lasers in the industry. other researchers. the lab, he picked up a later prototype with a medium- Over the laser’s 50-year history, Maiman’s place as sized flash lamp and 5 cm-long ruby rod, telling Mai- inventor of the laser has sometimes been acknow - man to “Hold this in front of your face and I know this ledged. In 1984 he was inducted into the National In- will be picked up by every news outlet, but if we print ventors Hall of Fame – meeting Kathleen, who became this, this first laser, it won’t go anywhere.” The photo - his second wife, on the flight home afterwards. Most grapher was right. The day after the press conference significantly, in 1987 he was awarded the Japan Prize, all the major newspapers carried the photograph – which is often considered the Eastern equivalent of along with, in one case, the melodramatic headline the Nobel. “LA man discovers science-fiction death ray”. But at other times, Maiman felt his role was down- Within the academic community, though, there was a played. It was Townes who shared the 1964 Nobel Prize certain amount of scepticism and confusion about what for Physics with two Russian theorists, Nicolay Basov Maiman had achieved. The optical quality of the crystal and Aleksandr Prokhorov, for “contributions to fun- in his first laser was poor and so he had not ob served damental work in quantum electronics leading to the the characteristic “pencil beam”. Instead, his early re - development of the maser–laser principle”. And in sults were based on sensitive spectroscopic measure- 1998, Bell Labs honoured Townes’ work again with a ments. Maiman also faced some degree of prejudice: major celebration to mark “the 40th anniversary of the people expected the advance to come from Bell Labs laser” – a reference to the 1958 “optical maser” paper, or one of the other well-funded research efforts, not rather than to the invention of a working device two 26 Physics World May 2010 physicsworld.com New from Oxford The uncomfortable truth is that The Many Worlds of Hugh Everett III Multiple Universes, Mutual Assured Destruction, and the Meltdown of a Nuclear Family for some of the people involved, Peter Byrne ‘This book has the potential to become the definitive even 50 years after the fact, biography of one of the finest minds of the twentieth century.’ - David Deutsch FRS, Oxford University the invention of the laser is May 2010 | 978-0-19-955227-6 | Hardback | £25.00 still controversial Quantum Electronics for Atomic Physics Warren Nagourney years later. ‘This is a well-written and readable introduction to For Maiman, the lack of recognition hurt, and it quantum electronics which treats topics not usually found in traditional texts. Nagourney has put together what could prompted him to write a memoir presenting his side become a standard book in the field.’ of the story. “Ted wrote his book because he felt that - Ifan Hughes, Durham University his place in history was not being properly addressed,” explains Kathleen. “And I still offer [anyone who asks] April 2010 | 978-0-19-953262-9 | Hardback | £45.00 The Laser Odyssey because it was directly from him and it’s correct.” Oxford Handbook of Nanoscience and In the book, Maiman hits back at his critics, assert- Technology ing that Bell Labs has little claim on inventing the laser Three-Volume Set because its proposal never worked: nobody has ever Edited by A.V. Narlikar and Y.Y. Fu been able to make a potassium-pumped potassium- vapour laser as described in Schawlow and Townes’ This is an agenda-setting and high-profile book that presents an authoritative and cutting-edge analysis of 1958 paper, and the patent based upon it never earned nanoscience and technology. any money. Indeed, Maiman attributes his success to the fact that he did not follow the teachings of Schaw - April 2010 | 978-0-19-957443-8 | Pack | £299.00 low and Townes; if he had, he would never have con- sidered pink ruby as a suitable laser medium. Lectures on Light Maiman’s attitude may sound harsh, but the uncom- Nonlinear and Quantum Optics using the Density fortable truth is that for some of the people involved, Matrix even 50 years after the fact, the invention of the laser Stephen C. Rand is still controversial. In a feature article published in ‘A textbook which thoroughly introduces the density matrix the January issue of Physics Today magazine, Nelson, formalism and applies it to a range of topics of current Robert Collins and Wolfgang Kaiser – three Bell Labs interest constitutes a "missing link" among quantum optics researchers who worked on early laser projects – des - textbooks.’ cribe “the work at Bell Labs in the summer of 1960 that - Christoph Becher, Saarland University, Germany led to the creation of the first ruby laser”. May 2010 | 978-0-19-957487-2 | Hardback | £39.95 Those claims disconcert Kathleen, who believes that Maiman’s position as creator of the first laser is beyond Atomic Force Microscopy dispute. “The Bell Labs scientists had a photo of Ted’s Peter Eaton and Paul West laser from the newspaper [and] the account that his A very practical guide which will demystify Atomic Force pink ruby crystal worked,” she says. “And Schawlow Microscopy for the reader, making it easy to understand, had obtained from Ted a copy of his unpublished sub- and to use. mission to Physical Review Letters describing the con- March 2010 | 978-0-19-957045-4 | Hardback | £55.00 struction of his laser. All of these facts combined would clearly mean that any subsequent construction and operation of a laser at Bell Labs was purely imitating what Ted had already done.” Statistical Mechanics Kathleen still keeps a notebook from the day, 16 May Theory and Molecular Simulation 1960, when Maiman made his laser breakthrough. She Mark Tuckerman acknowledges there have been some “sour grapes” over the years. Yet she has even stronger feelings about Treats both basic principles in classical and quantum statistical mechanics as well as modern computational the positive contribution Maiman made to society. methods, providing both model and real-world “I had great appreciation for Ted Maiman the man, a examples. loving husband and a delightful companion,” she says. February 2010 | 978-0-19-852526-4 | Hardback | £47.99 “But what I’m really finding extraordinary right now is Ted Maiman the scientist. I’m beginning to appreciate how there are moments in the history of humanity PHONE: +44 (0) 01865 353250 when an advance occurs that is so extraordinary and EMAIL: [email protected] un expected that the world for better or worse is 24-hour credit card hotline: +44 (0)1536 454534 1 changed forever. I think the invention of the laser on Visit our website: www.oup.com/uk 16 May 1960 marks one of these times.” 27 Physics World May 2010 National Ignition Facility 28 The laserat50:Laserfusion Physics World May2010 physicsworld.com physicsworld.com The laser at 50: Laser fusion Fusion’s bright new dawn As we celebrate 50 years of the laser, a milestone looms in the world of laser fusion. Mike Dunne describes how achieving ignition – fusion’s break-even point – with the world’s largest laser will transform the search for abundant, carbon-free electricity

Three days after Theodore Maiman demonstrated the first ruby laser at his laboratory in Malibu, California, in May 1960, a scientist a few miles away at the Law - rence Livermore National Laboratory came up with an idea for using lasers to harness the power source of the stars. Although details of Maiman’s device would not emerge for several weeks, scientists already knew that a laser’s ability to concentrate energy in time and space would be unprecedented. Might it be possible, the Livermore scientist wondered, to use lasers to fuse small atoms together to create a heavier, more stable atom – releasing huge amounts of energy in the process? Thanks to the levels of secrecy prevalent at the time concerning atomic matters, it would be another 12 years before the scientist in question, John Nuckolls, articulated his ideas about laser fusion for the broader scientific community. Writing in Nature, Nuckolls and his colleagues explained that in order for their scheme to work, a large-scale laser had to be built – one that could compress and heat the fusion fuel to a tempera- ture of 108 K and densities 1000 times that of liquids, con ditions that surpass even those found at the centre of the Sun. Nuckolls’ team predicted that a laser with an energy of 1 kJ and a pulse length of a few nanoseconds would be sufficient to initiate the process, although a much larger laser (a few megajoules, it was estimated) would be required to produce a substantial energy output. Sci- entific excitement over this idea – coupled with a suc- cession of energy crises in the 1970s and 1980s – led to the construction of a series of increasingly large lasers to test the concept. Unfortunately, these experiments proved that the journey would be much harder than pre- dicted: the threshold itself was likely at the megajoule level, thanks to the need to overcome a range of insta- bilities that hampered efforts to couple laser energy to Mike Dunne the fuel and then compress it to the required densities. is Director of the Yet after years of intermittent successes and setbacks, Central Laser Facility Ready, aim, fire we are finally entering a truly exciting period in the at the STFC A view inside the world of laser fusion. The past decade has seen un- Rutherford Appleton target chamber at precedented sums of money invested in the field, with Laboratory in Didcot, the US National the principal aim of demonstrating, once and for all, Oxfordshire, UK, Ignition Facility. that the science of laser fusion really works. The re- e-mail mike.dunne@ cently completed US National Ignition Facility (NIF), stfc.ac.uk 29 Physics World May 2010 The laser at 50: Laser fusion physicsworld.com

The National Ignition Facility that the Sun could get its energy from converting hy- drogen nuclei into helium nuclei, releasing just less than 1% of the mass as energy, according to Einstein’s famous equation E = mc2. Then, in 1939, Hans Bethe distilled these facts into a quantitative theory of energy production in stars, which eventually won him the 1968 Nobel Prize for Physics.

National Ignition Facility Although the Sun and other stars generate fusion by using their gravitational energy to compress hydro- gen (and subsequently heavier elements), for any ter- restrial effort it makes more sense to use a fuel source composed of deuterium and tritium. These isotopes of hydrogen contain one and two neutrons, respectively (figure 1). They have the highest cross-section for fusion since they have low charge (just a single proton each) and the proton and neutron(s) are not very tightly bound. In the basic fusion reaction, deuterium (D) and tritium (T) combine to form helium and a very energetic neutron: 2D + 3T → 4He (3.5 MeV) + n (14.1 MeV) The National Ignition Facility (NIF) is the world’s largest laser. Located at California’s In order for this reaction to take place, the particles Lawrence Livermore National Laboratory, it covers 70 000 m2 (roughly two football need to be moving at very high velocities to overcome pitches) and contains 8000 large optical units (each up to 1 m in diameter) and the Coulomb barrier, since the positive ions experience 30 000 smaller optics. These and other components are contained in approximately an increasingly strong repulsive force as they get closer 6000 modular units that can be replaced quickly when necessary to ensure and closer together. This means that the fuel needs to continuous operation of the facility. be heated to an incredible 108 K. Under these condi- Together, the facility’s 192 laser beams can deliver 1.8 MJ of energy with a tions, electrons are stripped from their parent nuclei, combined power of 500 TW (500 × 1012 W). This is about 40 times more power than turning the fuel into a plasma. the average consumption of the entire world, and a few times greater than the power The need to create high-temperature plasmas for of all the sunlight falling on the Earth. Of course, this power only lasts for a few fusion to occur explains why fusion is not a process nanoseconds, so it contains only a trivial amount of energy. But when this energy is we encounter in everyday life on Earth, and why it is delivered through multiple traversals of the 100 m long hall (see image above) and so incredibly difficult to harness as a net source of focused down to millimetre scales at the centre of a 10 m diameter “target chamber”, power. On a positive note, this does introduce one it is enough to create shock waves with pressures of tens of millions of atmospheres. major benefit: unlike nuclear fission, which can lead to This pressure makes the fuel pellet implode, forcing the atoms of deuterium and an uncontrolled “chain reaction”, the fusion process is tritium inside to fuse together. Getting it right requires a lot of effort; for example, the inherently safe since the fuel “wants” to be inert, and target chamber is held under vacuum to allow the lasers to be focused down to spots thus loses energy at any opportunity. And thanks to the just 1 mm in diameter, and the fuel pellet itself has to be extremely round and smooth, stars, we know categorically that fusion works – we just since any imperfection is exponentially amplified in the course of the implosion. need to find an alternative to the Sun’s use of gravity to provide the heating and confinement of our fuel. There are two principal routes to achieving confine- located at the same lab where Nuckolls had his big idea ment: we can either hold the plasma in a magnetic field 50 years ago, is among the most tangible results of this while heating it using radio waves or particle beams; or effort (see box above). And a little over a year after NIF we can compress it to unprecedented densities using officially opened, scientists there are now on the brink lasers. The first approach is being pursued through the of a breakthrough: crossing the required threshold for ITER magnetic-confinement fusion experiment cur- the instigation of a self-sustaining fusion reaction, lead- rently being built in Cadarache, France, while the latter ing to a net release of energy for the first time. is being studied at handful of labs – including NIF – The achievement of this 50-year-old goal – known using some of the world’s largest lasers. technically as “ignition” – will be a game-changing event that will propel laser fusion from an elusive phe- How laser fusion works nomenon of physics to a predictable, controllable, tech- The laser route to fusion neatly combines two of Ein- nological process ready to address one of society’s most stein’s most famous contributions to science: his explan- profound challenges: finding an enduring, safe and ation of stimulated emission; and his quantification of environmentally sustainable source of energy. The NIF the equivalence of mass and energy. The basic approach plan is to ensure that this milestone is reached within is a repetitively cycled system in which ball-bearing- the next two years. sized pellets of deuterium–tritium fuel (figure 2) are injected into the centre of a large, empty chamber. A Making a star in the lab number of powerful laser beams are used to compress The history of fusion can be traced back to 1920, when the fuel to densities of 1000 g cm–3, or about 100 times Francis William Aston discovered that four separate the density of lead, for a few millionths of a millionth of hydrogen nuclei are heavier than a single helium nuc- a second (10–12 s). Of course, this high-density fuel will leus. This occurs because the stability of helium leads subsequently blow apart – but not instantaneously. It to a lower overall rest mass. On the basis of this work, will persist at high densities on a timescale determined another British scientist, Arthur Eddington, proposed by its inertia and characterized by the time taken for a 30 Physics World May 2010 physicsworld.com The laser at 50: Laser fusion

1 Getting it together 2 On target

D He p n n n p p National Ignition Facility

T n p n n n The fuel pellets used in laser fusion are ball-bearing-sized hollow spheres made of beryllium (shown here), plastic or high-density In a nuclear-fusion reaction, molecules of deuterium and tritium – carbon. The pellets must be extremely round, with a very smooth isotopes of hydrogen with one and two neutrons, respectively – surface, since any irregularity will cause the laser beam to transfer combine to produce helium and an energetic neutron. energy to the fuel unevenly. sound wave to propagate across the imploded assem- excess neutrons to create a closed fuel cycle; however, bly. This “self-confinement” phenomenon has led to this can be achieved by adding other materials (princi- the process being called “inertial-confinement fusion”, pally lithium-7, beryllium or lead) to the blanket. and it gives the system sufficient time to allow a sub- On the laser side, Nuckolls’ original predictions that stantial fraction of the fuel (typically 30%) to be con- a relatively small-scale laser would be sufficient to cre- verted to helium and a neutron. ate the required conditions turned out to be correct The first fusion reaction produces a helium ion that only if there is freedom to drive the implosion at an deposits its energy in the neighbouring fuel, thus allow- arbitrarily high velocity. This is not possible due to vari - ing the high temperatures to be maintained and the ous unstable, nonlinear processes in which the laser can fusion reaction to propagate through the fuel. The high- set off electron or ion “waves” in the plasma, or cause energy neutron, however, escapes, since it interacts only the imploding fuel to break up prior to reaching high weakly with the charged plasma. The neutron’s energy compression. For example, when high-intensity lasers is therefore carried into a thick “blanket” of material heat matter, they can resonantly drive an oscillation surrounding the interaction chamber, heating the blan- in the plasma, thus causing the light to scatter off the ket to about 1000 K. In a fusion power plant, the process plasma wave and preventing the fuel from absorbing would be repeated about 10 times per second, and the it efficiently. If the laser intensity is too low, however, heat would be used to drive an advanced gas-turbine then the pellet implosion is driven at such a low velo - cycle, thereby generating electricity. city that any imperfections arising from surface rough- The physics underpinning laser fusion is actually ness or laser non-uniformities seed the growth of quite well understood. Moreover, thanks to a series of hydrodynamic instabilities, leading to total break up experiments performed by UK and then US scientists of the imploding shell prior to full compression. in the 1980s (see Physics World March p23), we know It has taken many decades to adequately understand that ignition and energy production can be attained these processes, and their existence has meant that a here on Earth if we have a sufficiently powerful driver. laser roughly 1000 times the scale originally envisaged These experiments, which used the X-ray output of an by Nuckolls has to be used. The lasers at NIF – which exploding thermonuclear bomb to implode the pellets, have been performing remarkably well in their initial can be viewed as the ultimate “swords into plough- phase of operation – are designed to mitigate the growth shares” demonstration. What remains is to prove that of these plasma and hydrodynamic instabilities. Much a laser can be used as the driving source, and to demon- attention has been paid to ensuring a sufficiently strate that the emitted fusion energy can be harnessed “smooth” laser beam, with control over its temporal at a level compatible with a full-scale power plant. profile to allow quasi-isentropic compression of the fuel The deuterium in the fuel pellet is sourced from by launching a series of precisely tailored shocks. Physicists are water, which naturally contains about one molecule of so confident D2O for every 6000 molecules of H2O. The tritium, in From fusion to electricity contrast, must be manufactured in situ by bombarding Fusion physicists are so confident that NIF will be able that NIF will lithium-6 atoms with neutrons, thereby transmuting to “ignite” a self-sustaining fusion reaction that atten- be able to the lithium into tritium and helium. Here, we can use tion is now turning to the endgame. The next problem “ignite” a a neat trick: if we construct the blanket surrounding the is how to best harness the emitted neutrons in a manner self-sustaining fuel pellet with lithium-6, we can use the neutrons pro- compatible with a robust, commercially viable power fusion reaction duced in the fusion reaction to generate more tritium plant. Such a plant would operate conceptually like a (as well as producing the heat for the electricity tur- car engine, with three key stages. that attention bine). In practice, it is a little more complicated than In the first step, fuel – in the form of a ball-bearing- is now turning this, because we have to ensure that there are enough sized pellet of frozen hydrogen isotopes, held at tem- to the endgame 31 Physics World May 2010 The laser at 50: Laser fusion physicsworld.com

Laser technology for fusion power The National Ignition Facility (NIF) is designed to although they are currently optimized for LULI provide the scientific evidence that large-scale continuous-wave operation, not pulsed. The lasers can ignite and burn a fusion fuel capsule, state of the art for pulsed laser systems is producing between 10 and 100 times more currently at the kilowatt level. The image shows “fusion energy out” than the amount of “laser a pulsed laser system at France’s Laboratoire energy in” required to start the reaction. In order pour l’Utilisation des Lasers Intenses facility, to harness this energy for a power source, the viewed through the focusing and guiding optics lasers at NIF would have to operate about to the pumped amplifier head. 10 times per second, with each beam delivering Many designs now exist for the required level an average power of 10–100 kW and a laser of operation for a laser-fusion system. Looking at efficiency (defined as “electricity in” per “laser NIF uses flash-lamp technology to pump its the rate of progress of pulsed laser systems, and energy out”) of about 10%. Such high levels are amplifiers – the devices that convert incoherent the substantial funding being attracted to this not possible at NIF, where laser efficiencies are “conventional” light into a high-energy laser area for a variety of applications, the next five less than 1% and the average power is beam via the process of stimulated emission. years are likely to see construction and approximately 1 W. Diode-laser-pumped solid-state amplifiers, in operation of a prototype beamline. As with NIF, However, existing laser technologies indicate contrast, have been shown to operate at up to multiple numbers of such beams would be that there is room to improve on these figures. 100 kW with efficiencies more than 10%, focused onto a millimetre-scale fuel pellet.

peratures of about 18 K – is injected into a multi-metre- in laser science, including the high-repetition-rate tech- diameter vacuum chamber. Next, a laser “piston” com- nology used in the welding and machining industry, and presses the fuel by heating the outer surface of the several ongoing high-power-laser research projects. pellet to create a hot, spherically expanding gas. In One example of the latter is the Extreme Light Infra- order to conserve momentum, the rest of the pellet is structure (ELI) project, a 7750m effort led by the forced to move rapidly inwards at velocities of more Czech Republic, Hungary and Romania (see pp12–13) than 105 m s–1. The degree of compression achieved in that seeks to create laser pulses with peak powers of this process is similar to squashing a basketball down up to a few hundred petawatts (about 1017 W) using to the size of a pea. the same type of diode-pumped laser technology that In advanced schemes – analogous to a petrol engine HiPER will require (see box above). – a separate laser is then used as a “spark plug” to Over the past few decades, lasers have developed at ignite the fuel at the instant of maximum compression. an incredibly fast pace, allowing fusion researchers to Adding in this extra laser could lead to a more efficient take advantage of rapid increases in power and effi- (higher gain) system, but it is not an essential require- ciency. Using lasers also allows us to adopt a modular, ment: if we compress the fuel enough, the compres- maintainable and easily upgraded approach to power- sion alone will generate enough heat to create a hot plant design during HiPER’s second phase, in which “spark” at the centre of the imploding fuel. When the we plan to build a facility that combines the scientific temperature is high enough, and enough mass has demonstration of ignition at NIF with high-repetition- been imploded to an appropriately high density, fusion rate laser technology. This modular strategy should is initiated in a self-sustaining manner. The helium reduce the timescale for construction, increase power- nucleus from one reaction heats the neighbouring fuel, plant availability throughout its life, and ensure that we while the neutron escapes to heat the external blanket find the most cost-efficient solution. to generate electricity. At the same time as Europe is devoting resources to The final step occurs when the spent fuel is exhausted HiPER, US scientists are planning a similar journey out of the chamber. At this point the cycle repeats. In with the aptly named LIFE project (Laser Inertial a car engine, the fuel cycle is repeated about 50–100 Fusion Engine). Led by the scientists who worked on times per second. The repetition rate for laser fusion NIF, this project has the same goal as HiPER: to is lower: 10 times a second would be enough to produce demonstrate the required high-repetition-rate tech- electricity on the gigawatt scale, comparable to the nology, integrated into a power-plant-scale facility. largest coal, gas or fission power stations. However, Scientists in Japan, meanwhile, have well-defined plans that rate is simply not possible with NIF, which fires for demonstrating the “petrol engine” approach to only once every few hours. New technology is needed power generation described above. Thanks to these to convert the scientific demonstration on NIF into a efforts, it is looking increasingly likely that reaching constantly cycling system that can generate electricity. ignition at NIF will remove the question of whether One project that aims to bridge the gap between laser-fusion power will be achieved, to replace it with achieving ignition and building a practical fusion power the more political question of who is likely to deliver plant is the High Power laser Energy Research facility, the first working power plant. or HiPER. Led by the UK and involving a 10-nation consortium of researchers and funding bodies, HiPER’s Towards a working power plant goal is to demonstrate the 10 Hz level of performance The achievement of ignition at NIF will provide the of all the component technologies for power-plant-scale ultimate verification of the scientific basis of laser- operation within the next 10 years. To do this, we hope fusion energy, marking the culmination of 50 years’ to draw on innovations that are taking place elsewhere effort. Yet the second milestone – a working fusion 32 Physics World May 2010 physicsworld.com The laser at 50: Laser fusion power plant – is the real goal, motivated by the demand topics range from studies of astrophysical processes such Pursuing a for a sustainable, low-carbon economy. As we have as nucleosynthesis, cosmic-ray generation, proto-stel- future energy already seen, the principal ingredients in fusion are lar jets and planetary-nebulae formation, to the research source based deuterium, which is found in water, and lithium, which into the cores of gas-giant planets and the origins of occurs naturally in igneous rocks and some types of the Earth’s magnetic field. The lasers could also under- on lasers still clay, as well as in seawater. The Earth contains enough pin a host of fundamental studies in areas as di verse as faces huge of both ingredients to last for millennia. In fact, based atomic physics, nuclear science, turbulence and the cre- technological on current rates of electricity consumption in the UK, ation of macroscopic quantities of relativistic matter. challenges just one bathtub of water and the lithium from two lap- Perhaps just as importantly, the component tech- top batteries would provide enough electricity for an nologies used in fusion research – not least the highly individual’s entire lifetime. efficient, high-power lasers themselves – open up a wide Furthermore, fusion produces no greenhouse-gas range of spin-off opportunities. These range from secur- emissions and has a low environmental impact over the ity screening for nuclear materials at ports and the pro- life-cycle of a plant. The chief waste product is inert duction of medical radioisotopes to the treatment of helium gas, and the residual radioactivity at the plant deep-seated tumours via particle-beam therapy, the itself should be manageable using conventional de- processing of materials for the aerospace industry and commissioning techniques over a period of 100 years. even the development of next-generation light sources. Fusion plants will have power outputs of as much as Pursuing a future energy source based on lasers still 1–2 GW, making them ideally suited as large, central faces huge technological challenges in advanced ma - facilities on the existing electricity-grid infrastructure. terials, micro-scale engineering, laser technology and Other benefits include the high-temperature environ- integrated power-plant systems. But the wider market ment of the blanket, which could be used to generate for the high peak-power, high average-power laser sys- hydrogen for fuel cells or even to desalinate water. tems allows the fusion field to build from a well-devel- These wider applications, as much as their electricity oped in dustrial base, and to borrow advances from output, may be the crucial factor that will determine other projects to accelerate the timescale to delivery. the commercial viability of early fusion power plants, We have been waiting 50 years for the scientific proof and thus the timescale for delivery of the first genera- that controlled fusion works. Now that this proof tion of facilities. is almost upon us, we need to make sure we capitalize In the meantime, laser facilities used in the pursuit on it to ensure that we do not have to wait a further of fusion can also be exploited for pure research. The 50 years to see it used.

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33 Physics World May 2010 Light fantastic

The laser has become so ubiquitous that it would be impossible to acknowledge everyone who has played a role in its success. As Roy Glauber said at the 2005 Nobel-prize banquet, when it comes to lasers, “many hands make light work”. And he should know: the prize Glauber shared with fellow optics pioneers John Hall and Theodore Hänsch is one of more than 10 Nobels awarded (so far!) for laser-related research. This timeline marking 50 years of the laser contains Physics World’s pick of events from laser history, including prizes (gold text), applications (green) and “firsts” (blue). 1950

A team led by Charles Townes builds the first “maser”, a forerunner of the laser that had been described theoretically (and independently) by 1953 Nikolay Basov, Alexander Prokhorov and Joseph Weber in 1952. Basov, Prokhorov and Townes share the 1964 Nobel Prize for Physics for their work on the “maser–laser principle” Gordon Gould coins the term “laser” in his lab notebook. The entry becomes the basis of a 30-year patent dispute 1957

Theodore Maiman builds the first functioning laser, observing lasing action in a crystal of pink ruby (16 May) William Bennett, Donald Herriott and Ali Javan invent the helium–neon gas 1960 laser, the first to produce a continuous beam of laser light (12 December) 1961 1962 Charles Campbell and Charles Koester perform the first laser surgery, destroying a human patient’s retinal tumour using a ruby laser Robert Hall invents the semiconductor diode laser

Lasers are used to align a subway tunnel beneath San Francisco Bay 1966

1970 Dennis Gabor wins the Nobel Prize for Physics for developing holography The first large-scale laser light shows are staged 1971 Military laser target designators are used for the first time, during the 1972 Vietnam War 1974 First trials of laser supermarket bar-code scanners

John Madey invents the free-electron laser 1976

ilio Segrè Visual Archives; Mehau Kulyk/Science Photo Library; Martin Dohrn/Science Photo Library; Shuji Nakamura; Massachusetts Institute of Technology; Adam R Contos The first commercial laser-disc player, made by Philips, goes on sale. 1978 High costs mean the 12-inch disc format never really takes off. Philips has better luck with the audio compact-disc player, which hits the market in 1982 1980 Nicolaas Bloembergen and Arthur Schawlow share the Nobel Prize for Physics 1981 for their “contribution to the development of laser spectroscopy” US President Ronald Reagan’s “Star Wars” speech reignites interest in 1983 weapons-related lasers Steve Chu, Claude Cohen-Tannoudji and William Phillips develop techniques 1985 for cooling and trapping atoms using laser light. The trio share the 1997 Nobel Prize for Physics

TAT-8, the first transatlantic fibre-optic cable, is completed, linking 1988 North America and Europe. The first fibre-optic cable for inter-office communications had appeared 13 years earlier, when police in Dorset, UK, turned to Standard Telephones and Cables after a lightning strike knocked 1990 out their radio-transmitting equipment

Slow down! Lasers are used in the UK to inform drivers of excessive speed 1994 Shuji Nakamura demonstrates the first blue laser diode 1996 Researchers led by Wolfgang Ketterle create the first “atom laser” using a 1997 Bose--Einstein condensate (BEC). In 2001 he shares the Nobel Prize for Physics with Eric Cornell and Carl Wieman, who in 1995 had been the first to observe a BEC in a dilute gas of atoms 2000

The first laser “guide star” is used at the KeckII telescope in Hawaii 2002

Blu-ray discs introduced 2006

Charles Kao shares the Nobel Prize for Physics for his work on fibre optics 2009 Experiments aimed at achieving “ignition” – the break-even point for nuclear 2010 fusion – begin at the US National Ignition Facility. The world’s largest laser is expected to reach this milestone within the next two years Image credits (top to bottom): American Institute of Physics/Science Photo Library; Emilio Segrè Visual Archives/American Institute of Physics/Science Photo Library; General Electric Research and Development Center, Emilio S The laser at 50: Boom, bust, boom physicsworld.com The bubble legacy

The technology crash of the early 2000s may have left many companies bruised, burned or broken, but several key advances in laser technology from that time are now bearing fruit, as Jeff Hecht explains

Jeff Hecht is a Imagine an optics company – let’s call it JDS Uniphase a stone (figure 1). freelance science – with a market capitalization approaching the gross In retrospect, it was an investment bubble as daft and technology writer domestic product (GDP) of Ireland. Now imagine it as the Dutch tulip bubble of the 17th century or the based in Auburndale, merging with a laser company – say, SDL – that has British South Sea bubble of the 18th century. The Massachusetts, a stock valuation of $41bn, higher than the GDP of money largely evaporated as the bubble deflated. With- US, e-mail jeff@ Costa Rica. Finally, imagine a start-up with $109m in in a year, $1000 invested in Nortel stock had shrunk to jeffhecht.com. He is author of the book venture capital in its pocket but no product to its name just $72. As one wry observer noted, investors would City of Light, which (Novalux) turning down an offer of $500m as insuf- have done better investing $1000 in Budweiser – the covers the history ficient. It may be hard to believe, but these tales are beer, not the stock – and cashing in empty bottles at of fibre optics true: they occurred in the year 2000 – an era when the 5 cents each. Today, JDS Uniphase is one of the lucky (2004 Oxford laser, fibre-optics and photonics industries were the companies still in business, with a market capitalization University Press) darlings of the financial world. Such was the madcap of $2.5bn, about 2% of its peak value. It has dropped in nature of that brief period that survivors call it simply value by more than $100bn – more money than vanished “the bubble”. in the Madoff swindle – while Nortel has gone bust. The bubble was born as the Internet took off in the But for every cloud there is a silver lining. The vari- mid-1990s, pumped up by the explosive growth of the ous laser-based technologies that emerged from the World Wide Web. Investors first noticed the “dot-com early Internet boom have become crucial both within companies”, which were easy to caricature as a few peo- the telecoms industry and beyond. ple with a website and a warehouse. But financiers’ interest soon spread to other companies in the wider The quest for bandwidth telecoms market, particularly firms making equipment The dot-com bubble was built on the development of to build the “information superhighway”. By March fibre-optic cables, which became the backbone of the 2000, investors were eagerly pouring barrelfuls of global telephone network in the 1980s. Such cables – money into new optical technologies for a booming essentially bundles of parallel glass fibres that carry telecoms market. light – allowed more data to be sent over longer dis- But the clock began ticking after the technology- tances than was possible with previous microwave heavy NASDAQ index of small-company stocks relay towers or copper-cable systems. It was fibre-optic peaked above 5000 during one week in March 2000 cables that carried the explosive growth of Internet that saw investors mobbing that year’s Optical Fiber traffic in the mid-1990s, which in turn created a huge Communications Conference in Baltimore. First to fall demand for yet higher transmission capacities. In about were the dot-com firms – the companies “selling dog 1999, Internet traffic was said to be doubling every food on the Internet”, as chief analyst John Ryan from three months, although a later analysis by mathemati- market-research firm RHK Inc. so eloquently put it. cian and communications researcher Andrew Odlyzko, Businesses making communications hardware initially now at the University of Minnesota in the US, revealed seemed less of a risk, but that did not stop the optical that this rate was achieved only briefly in 1995–1996. industry from also running off a cliff, where it hung sus- Still, the perception of a huge transmission demand pended in mid-air with its legs churning like the car- fuelled heavy investment in new optical technologies toon character Wile E Coyote – until it looked down that could provide the sought-after bandwidth. and the law of gravity took hold. Start-ups crashed, with In fact, the two innovations that would prove central their remains sold on eBay for pennies on the dollar. to increasing fibre-optic bandwidth – namely, optical- Sales of the diode lasers used in telecoms dropped like fibre amplifiers and wavelength-division multiplexing (WDM) – were actually developed before the dot-com The various laser-based technologies boom. The first of these innovations came as a response to the problems with the fibre-optic cables of the 1980s, which could carry only one signal wavelength per fibre that emerged from the early and needed “electro-optic repeaters” to be stationed roughly every 50 km to maintain signal strength. These Internet boom have become crucial repeaters converted an input optical signal into elec- trical form, before amplifying the signal and then turn- both within the telecoms industry ing it back into optical form – a cumbersome and costly process. Optical-fibre amplifiers, in contrast, could and beyond amplify an optical signal directly. 36 Physics World May 2010 physicsworld.com The laser at 50: Boom, bust, boom The NASDAQ OMX Group, Inc.

As for WDM, it allowed one fibre to simultaneously diode lasers were developed that could emit light Money talks transmit many signals at different wavelengths, some- centred on 980 nm and 1480 nm – the wavelengths The NASDAQ index of thing that had been impractical with electro-optic needed to excite erbium. Meanwhile, new optical tech- small-company repeaters. The idea of WDM had been around for niques were developed to divide the erbium-amplifier stocks peaked years, but had not been viable because the different band into narrower segments, each containing a sep- at 5079 in March wavelengths had to be physically separated for am - arate signal. Initially, the signals were a few nanometres 2000, fuelled by developments in plification at every electro-optic repeater. That all apart, but soon they could be separated by just 0.4 nm, laser technology. changed in the mid-1980s when David Payne at the thereby squeezing dozens of signals into a 25 nm band. University of Sout hampton in the UK invented the By the mid-1990s, a rapidly growing army of research - erbium-doped fibre amplifier – an optical fibre in ers working on these and other technologies had made which the silica light-guiding core has been doped erbium-doped fibre amplifiers practical. with erbium atoms. Light from a “pump” laser directed Although slicing the erbium-amplifier spectrum into along the length of the fibre excites these erbium atoms narrower bands was good because it increased the to a state that naturally emits infrared light at a range of number of slots available for transmitting WDM sig- wavelengths centred on 1550 nm when stimulated by a nals, it placed more demands on the diode lasers used weak input signal. This multiplies the strength of any as transmitters. Initially, lasers were made that emit- signal transmitted over a band of wavelengths some ted precise fixed wavelengths in the middles of the 25 nm wide – broad enough to allow signals at several standard WDM channels, which annoyingly meant different wavelengths to pass along the same fibre. that a different diode laser had to be used for each Early erbium-doped fibre amplifiers were pumped WDM channel. By 1998, however, tunable diode lasers by large and expensive lasers, but soon smaller, cheaper appeared to be the answer and investors started flock- 37 Physics World May 2010 The laser at 50: Boom, bust, boom physicsworld.com

1 Lasting legacy Coldren has personal experience of the telecoms bubble, having founded a company in 1998 called 10 Agility Communications to produce tunable diode 8 lasers in which the wavelength of the light emitted is 6 selected by slightly expanding or contracting the mul- diode tilayered reflective structures that make up the diode. 4 Laser Focus World “Agility was worth a lot of money before it [even] had $ (billion) 2 non-diode a product or a customer,” says Coldren, who had in- 0 vented the diode-tuning technique a decade earlier. 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 Investors poured more than $200m into the firm and Coldren stayed with the company until it was bought 100% by JDS Uniphase in 2005 for $67m in stock and cash – 79% a third of the money it had burned through. Although it took years to make tunable diode lasers as 50% 27% 25% good as fixed-wavelength diodes and to package them 15% 10% with control electronics for system use, sales did, how- 1% 2% 7% 0% ever, eventually begin to rise once the packaged tunable lasers beat the price and performance of fixed-wave- –24% –36% length lasers. Indeed, Coldren is sure that such tunable –50% lasers will be around for years to come. “We even use Laser sales peaked at the height of the bubble in 2000, then dropped dramatically as the them here at the university because they’re robust, easy telecoms market collapsed (upper graph). These year-by-year totals show that sales of the to make and very forgiving,” he says. Their design in- diode lasers used in telecoms are still less than two-thirds of their bubble-era peaks, when herently yields a single frequency – all it takes is tuning carriers paid premium prices to build what turned out to be excess capacity. By the time and calibration to obtain a desired wavelength. Even demand recovered and construction resumed, prices had come down. The lower graph shows first-year graduate students can do it, Coldren explains. the year-on-year percentage rises or falls in total sales. Despite the fluctuations, the cumulative annual growth rate over the period shown was 7%. Pumped by success Another bubble-era technology that has proved a hit ing to the companies developing them. As the bubble beyond the telecoms sector is the high-power diode grew, investors even chased half-baked ideas such as lasers that were originally designed to pump fibre am- “all-optical networking”, which envisioned redirect- plifiers. These lasers have since been adapted to pump ing the signals by changing their wavelength, but those a growing variety of solid-state lasers, which previously schemes came to naught. had been pumped by bright lamps. This process was inefficient because much of the lamp energy was emit- Telecoms technology ted at wavelengths not absorbed by the laser material. The telecoms bubble eventually collapsed because the Laser pumping is, in principle, much better because the market had wildly overestimated the demand for tele- laser can be fabricated to emit only light matching the coms capacity. Investors had funded too many com- absorption lines of chosen solid-state materials. panies doing similar things, while network operators Although early diode lasers could convert a larger such as AT&T and Verizon had installed far more fibre fraction of input power into pump light than was poss- than they needed, and it took years for demand to ible with lamps, they still only emitted milliwatts of catch up. Yet the crucial technology – laser transmit- power. Undeterred, military agencies took a keen ters, fibre amplifiers and “closely packed” WDM interest in developing more powerful pump diodes in optics that could cram in dozens of different wave- the 1980s and 1990s, realizing that such devices could lengths into a single fibre – worked fine. Recent years be used to pump lasers that mark targets for smart have even seen data rates start to climb again. The first bombs, or perhaps for laser weapons. But during the step was to 40 Gbits s–1 per wavelength and in Decem - dot-com bubble, when building pump diodes for fibre ber 2009 Verizon switched on a system transmitting at amplifiers appeared more lucrative, companies like 100 Gbit s–1 on a single wavelength between Paris and SDL started switching their attention from the defence Frankfurt – enough capacity to send 2.5 fully packed to the telecoms market. single-sided DVDs in a single second. That meant moving away from the 808 nm gallium– Tunable diode lasers have been another major win- arsenide pump diodes sought for military applications ner. They have largely replaced fixed-wavelength and focusing instead on a new family of indium– diode lasers in WDM systems because they are one- gallium–arsenide (InGaAs) devices that emit in the size-fits-all components. When a system is installed, 980 nm erbium pump band, as well as indium–gallium– software adjusts the lasers so that they emit at the de- arsenide–phosphide (InGaAsP) devices emitting at the sired wavelengths, then locks them in place. Although 1480 nm erbium pump band. That new focus was one some tunable lasers are used in subsystems where their reason why SDL – the biggest manufacturer of pump wavelengths may be changed when the network con- diodes – was worth a staggering $41bn when JDS Uni - figuration is altered, most tunable lasers are set to one phase announced plans to buy it in July 2000. wavelength and left there. “It’s sort of a dull use of tun- Market valuations have declined since those heady ability,” says optoelectronics engineer Larry Coldren days, but pump-diode technology has boomed, and of the University of California, Santa Barbara. It does not only in fibre amplifiers for telecoms. Pump diodes though fulfil system requirements. are displacing the pump lamps long used to power 38 Physics World May 2010 physicsworld.com The laser at 50: Boom, bust, boom neodymium-doped solid-state lasers, while today’s 2 Spin-off success green laser pointers are miniaturized frequency-dou- bled neodymium lasers, pumped by battery-powered laser cavity active region Bragg mirror diode lasers. (They are not strictly green lasers as they intracavity do not generate green light; instead, they take infrared elements light and double its frequency using nonlinear crystals heat so that it emerges as green.) At the opposite end of the sink power scale, the US defence firms Northrop Grumman output and Textron Systems have each demonstrated 100 kW substrate coupler solid-state laser weapons pumped by diode lasers. semiconductor These much more powerful lasers – which could be disk used to track, illuminate and then ignite enemy rock- ets, artillery and mortars up to a couple of kilometres pump optics John-Mark Hopkins, University of Strathclyde away – are much smaller and easier to use than they would be without pump diodes. semiconductor-diode pump laser quantum wells Variations on a theme Diode pumping has also been the key to success for a variation on another bubble-era technology: a novel type of semiconductor laser called the vertical-exter- One successful technology from the telecoms bubble of the early 2000s is a novel type of nal-cavity surface-emitting laser (VECSEL) that had optically pumped semiconductor laser known as the vertical-external-cavity surface-emitting originally been developed by researchers at the Massa - laser (VECSEL). At the heart of these devices (left) is a series of sandwich-like layers of chusetts Institute of Technology’s Lincoln Labor atory. semiconducting material – known as quantum wells – sitting on top of an internal “Bragg” The laser light in a VECSEL emerges from the top of mirror that is deposited in turn on a substrate such as the “III–V” semiconductor gallium a wafer, not from the edge as in usual diode lasers, and arsenide. As shown on the right, the light emerges from the top of the device, not from the edge the device contains one external mirror and one at the as in usual diode lasers. The VECSEL is pumped by light from a semiconductor diode laser, bottom of the chip. while a “heat sink” – a metal block or slab – conducts heat generated from the VECSEL away During the bubble, Aram Mooradian – a Lincoln Lab and it is cooled either by flowing water or simply air convection. The “output coupler” is a mirror alumnus – landed over $100m in venture capital to that transmits some light and reflects the rest back into the laser cavity to produce oscillation, set up a company called Novalux to build electrically while the “intercavity elements” are one or more optical devices that in this case double the pumped VECSELs for telecoms. That market never frequency of light generated in the VECSEL. got off the ground, and, after burning through $193m in venture capital, the firm was finally sold in 2008 for a core, so that most of the pump energy is converted into mere $7m to Arasor International, an Australian start- laser output. With the best materials, the conversion up. Its shares were last seen selling for 2 cents each. efficiency can reach 80% in the lab – impressively high However, diode-pumped VECSELs – also known by laser standards. Another benefit of this fibre geom- as optically pumped semiconductor lasers – are doing etry is a large surface-area to volume ratio, easing the much better, having become a hot new approach to removal of waste heat, which has been a problem with making visible solid-state lasers (figure 2). The big ad- bulk rod or slab solid-state lasers. vantage of optically pumping a semiconductor laser in Bubble-era developers looked at many rare-earth this way is that the laser can generate wavelengths it dopants for optical fibres. Ytterbium is the most at - cannot produce if it is pumped electrically. One leader tract ive for high-power operation because it can be in the field is the US firm Coherent, which has used this diode pumped using light at wavelengths only slightly approach to generate watt-range powers at, for ex- shorter than the output wavelength, which means that ample, an infrared wavelength of 1154 nm that can be the emitted photons can contain more than 90% of the doubled in frequency in a nonlinear crystal to create a pump-photon energy. (The total pump efficiency is, yellow 577 nm beam. This wavelength is important in however, limited to no more than 80% because not all treating diabetic retinopathy, a common cause of blind- of the excited atoms emit laser photons.) Ytterbium ness arising from the spread of abnormal blood vessels emits light at wavelengths of about 1030 nm, close to across the retina. When the laser illuminates the retina, the 1064 nm emission of neodymium, which means that oxygenated haemoglobin in the blood vessels absorbs ytterbium-fibre lasers with higher power and efficiency its emission, heating and destroying the vessels. could replace widely used neodymium solid-state lasers for many applications. The power of fibre Fibre lasers can reach impressive power levels. IPG But easily the most successful bubble-era spin-off are Photonics, for example, has built fibre oscillator ampli- fibre lasers, which now deliver kilowatt-class powers fiers with single-mode powers of 10 kW and multimode for industrial applications and ultrashort pulses for powers, with much lower beam quality, of 50 kW. Those research. Like fibre amplifiers, fibre lasers use rare- are among the highest powers available from any com- earth-doped fibres pumped from their ends by diode mercial laser. Although some of its lasers are so power- lasers. The rare-earth metal is confined in a small inner ful that military agencies have field-tested them for the core with high refractive index, which is surrounded by destruction of improvized explosive devices and un - an outer core made of lower-index glass that confines exploded ordnance on the battlefield, IPG’s main busi- light from the pump diodes. The dual-core structure ness is selling lasers that can be used in industry for passes the pump light repeatedly through the inner applications such as cutting metals (figure 3). Fibres 39 Physics World May 2010 The Little Book physicsworld.com of String Theory Steven S. Gubser 3 At the cutting edge “This is an engaging and concise introduction to the main ideas in string theory. Gubser gives us a quick tour of the basic laws of physics as we understand them today, and then demonstrates how IPG Photonics string theory seeks to go beyond them. He serves as an artful and attentive guide, as the reader explores the mysteries of quantum mechanics, black holes, strings, branes, supersymmetry, and extra dimensions in the pages of this book.” —Juan Maldacena, Institute for Advanced Study

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ad with strap.indd 1 30/3/10 09:06:17 physicsworld.com The laser at 50: The green gap Patrick Landmann/Science Photo Library

Going for green With manufacturers keen to start selling us mobile phones that can project TV pictures onto any nearby surface, a race is on to develop tiny diode lasers that can emit green light. Andy Extance reveals the challenges involved in bridging the green gap

Thousands of times per second a point of light turns they need to use. Their motivation for undertaking this on and off, moving side to side, top to bottom. It is a quest? The rewards available from enabling projectors rhythm that ticks around the world, illuminating living that can penetrate the billion-unit-a-year mobile-phone rooms and office desks in the process. However, the market. If they succeed, we could soon be using gadgets cathode-ray TVs and monitors that metronomically added to our phones – just like digital cameras have fire electron guns at viewers – who are shielded only been – to watch TV projected onto any nearby surface, by thin sheets of glass – are rapidly being replaced by from the convenience of wherever we happen to be. flat-screen technologies. Yet as the creation of images using scanning electron beams fades into history, a new Double trouble form of technology is emerging that builds up pictures The tiny semiconductor diode laser is familiar to us by scanning with light. from its use in CD and DVD players, and the more re - “One target is that everyone has the chance to share cent excursion into Blu-ray. But while lasers in these visual information at any time, in any location,” says devices can generate light at infrared, red and blue- Uwe Strauß, director of semiconductor lasers at Ger- violet wavelengths, respectively, there are still no green many’s Osram Opto Semiconductors. The firm is try- diode lasers widely available for the commercial ing to create green diode lasers suitable for use in “flying market. While green diode lasers do exist in research spot” projectors. These devices use a mirror to combine labs, they are only just crossing into the green spectrum red, blue and green laser light into a single beam, which from the blue, and with tiny power outputs of only a few scans back and forth rapidly. The light creates an image, milliwatts, they are not useful commercially (figure 1). pixel by pixel, that remains in focus regardless of the dis- However, do not get the impression that green laser tance to the surface onto which it is shone. light cannot be created or that it is not currently used To fabricate green laser diodes – millimetre-sized for practical purposes: it can be made by using large and Andy Extance is semiconductor chips containing all the necessary com- expensive gas lasers or by firing red light at special a science writer ponents to emit laser light – the Osram team and its “frequency doubling” crystals. These lasers are used in based in the UK, rivals must first tackle nanometre-scale defects and medicine, for example, because green laser light can e-mail aextance@ complex electronic phenomena in the materials that penetrate human tissue only to a very shallow depth. It supanet.com 43 Physics World May 2010 The laser at 50: The green gap physicsworld.com

1 The green gap higher-energy conduction band and positively charged holes from the valence band into an area of the device known as the quantum well. As the electrons then fall into the valence band, they recombine with the holes and light is emitted at a wavelength corresponding to the energy difference between the two bands. Highly 1000 reflective surfaces surrounding the quantum well form a laser cavity, trapping the light, which stimulates more electrons and holes to recombine, thus amplifying the emission. Light typically exits such devices at the edges of the quantum well. 100 Gallium arsenide phosphide (GaAsP) was the first light-emitting semiconductor to prove commercially successful, initially in red light-emitting diodes display- ing numbers on calculators and wristwatches in the

maximum output power (mW) 1960s. From the mid-1970s onwards the same material 10

S Nakamura and H Ohta, University of California, Santa Barbara was used in the development of laser diodes for optical networking and CD players. The emitted wavelength can be altered by changing the proportions of arsenic and phosphorus, which in turn alters the semiconduc- 1 tor’s band gap. When the ratio of arsenic to phosphorus 380 420 460 500 540 580 620 660 700 is 65:35, the band gap is about 1.97 eV, emitting 630nm lasing wavelength (nm) red light. Various colours of visible light have been achieved with laser diodes, but there is a gaping hole To make working lasers, manufacturers must limit at green wavelengths. Scientists are trying to solve the problem by tweaking their designs of the number of a type of defect known as a dislocation in blue laser diodes (based on gallium nitride and indium gallium nitride), but as greener the semiconductor crystal, because electrons and holes wavelengths are reached, the output power falls dramatically – below the 50 mW that device can recombine at these defects without emitting light. manufacturers are demanding. On the other side of the gap, researchers are not going for green For lasers based on GaAsP, there is a critical limit of but instead for high power in their red laser diodes (made from aluminium indium gallium about 10 000 dislocations per square centimetre, above phosphide), which explains the steep vertical drop-off on this side. This graph shows published which insufficient light is produced to allow lasing. data for laser diodes up to March this year. Almost 50 years of research has ensured that defect lev- els of below this are routinely achieved in today’s red can be used to precisely vaporize swollen prostate-gland and infrared laser diodes, allowing low-cost devices to blockages stopping urine flow in men and to reduce the be produced. pain felt by patients being treated for retinal damage. After the development of GaAsP devices, research These lasers, however, would be impractical for use in into other visible wavelengths largely focused on semi- mobile phones. conductors such as zinc selenide to try to achieve blue The problem is that even miniaturized frequency- and green light. In the 1990s these were overtaken by doubling lasers are both bulky and power-hungry in blue light emitters made from gallium nitride (GaN), comparison with laser diodes. The extra components which had previously been overlooked by many re- needed – a semiconductor laser that takes light from searchers as it was difficult to produce with good crys- an 808 nm laser diode and converts it to 1060 nm, tal quality. That was until Shuji Nakamura, then of before a crystal halves this wavelength to 530 nm green Japanese light-emitting diode and laser-diode maker light – make the overall device relatively bulky at about Nichia, and now of the University of California, Santa 400 mm3. Red and blue diode lasers, in comparison, Barbara (UCSB), discovered that it could perform well are about 30 mm3 in size. “It would be nice to have a even with 10 000 times more dislocations than GaAsP. green laser at this small size,” says Strauß. Although GaN’s 3.4 eV band gap can nearly produce the 405 nm the small green lasers used in laser pointers and in violet emission used for Blu-ray players without further some of the projectors found mounted in lecture alteration. However, to get a band gap corresponding theatres are frequency-doubled lasers, they would to longer “true blue” wavelengths of about 450 nm drain battery power from phones too quickly to be- requires added indium, while green wavelengths above come the world-conquering display technology that the 510 nm minimum needed for projectors require still Osram envisions. “If you want to watch a show on your higher indium contents. Unfortunately, when there is mobile phone, you need to be able to project for at too much indium, the large number of dislocations be - least one hour,” ex plains Strauß. “This means you comes a real problem. need to control power consumption.” Laser diodes are produced using crystal-growth Microvision Inc. techniques collectively known as epitaxy, in which Problematic materials materials are fabricated atomic layer by atomic layer, Portable projection The wavelength of light that a laser diode emits is in typically at high temperatures and under vacuum con- Projectors for part a fundamental property of the semiconductor crys- ditions. The GaN is grown on thin circular wafers inclusion in mobile tal from which the diode is made. It is determined by known as substrates, which are sliced from a larger phones are driving the separation between the conduction and valence cylindrical crystal “boule”. Including indium degrades the development of energy bands that electrons in a semiconductor can the quality of the material, so balancing the amount of green diode lasers. inhabit. The diode design injects electrons from the indium (to get longer wavelengths) with the crystal 44 Physics World May 2010 physicsworld.com The laser at 50: The green gap quality (affecting lasing ability) is a challenge. “The 2 Plane as day problem is that indium is grown at a lower tempera- ture than gallium nitride,” Strauß explains. “Low tem- perature means low crystal quality.” N non-polar Poles apart Another key challenge arises from a different funda- mental property of indium gallium nitride, namely that

the electrons and holes in the material can be unevenly non-polar distributed. The resulting imbalance in electronic charge creates an electric field known as a polariza - polar tion field. When GaN laser diodes are deposited on Ga standard substrates, a polarization field runs through the device in the direction perpendicular to the sur- The wavelength of light emitted by laser diodes grown on gallium nitride (GaN) surfaces is face. The field is created by an excess of electrons on influenced by the orientation of the crystal they are made on. The GaN unit cell (left) can be cut the top surface of the device and a deficit on the bot- along different crystal planes (right) to affect the direction of an ever-present polarization field tom. The interaction of the polarization field with the running through the laser diode. Diodes grown on a polar surface have this field running material on a quantum-mechanical level – known as vertically through the device. This narrows the band gap, thus allowing green emission at low the Stark effect – narrows the band gap, which is useful currents, although at higher currents the polarization field is masked, widening the band gap as it pushes the wavelength of the light emitted further and moving emission into bluer wavelengths. Diodes grown on non-polar surfaces do not suffer towards green. However, the field also comes with from this variation. However, without the polarization field, higher proportions of the gallium drawbacks. It makes it harder for electrons and holes must be replaced with indium to achieve the correct band gap to produce green light. This is also a challenge as it is difficult to make working laser diodes with high indium contents. to meet in the quantum wells of both laser diodes and Semi-polar surfaces, cut at angles between vertical and horizontal, present a compromise, with light-emitting diodes. Instead, the electrons and holes some also able to accommodate particularly high indium contents. are more likely to recombine and re lease energy as heat. “That’s wasted charge,” says Jim Speck, a ma- terials scientist at UCSB. Another difficulty is that screening caused by current flow that can push green when current flows through the laser, it creates an elec- lasers back into the blue seen in conventional sub- tromagnetic field that screens the electrons in the strates. Using this approach, Stephan Lutgen, Osram’s quantum well from the polarization field, widening the head of nitride-laser development, was able to present band gap again and shifting the emitted light back 50 mW output 515 nm lasers at the Photonics West con- towards blue. ference in San Francis co in February this year. UCSB researchers were among the first to show that It is not known why, but slicing the GaN boule in dif- changing the crystal direction along which GaN sub- ferent directions can also help to increase its indium strates are sliced – and so modifying the direction of content. Substrates produced from a plane inclined at the polarization field in diodes grown on them – 58° from the conventional orientation allow the high- improves laser-diode performance (figure 2). Cutting est indium content of all orientations, Speck says. wafers vertically rather than horizontally from the These substrates are semi-polar, but here the polar- boule means that diodes fabricated on them have the ization field brings the electrons and holes together, direction of the polarization field similarly rotated by rather than separating them. “The electric field is 90°. The substrates are therefore called “non-polar” as, working with the diode,” Speck explains. “The physics oriented in this direction, the polarization field no is more favourable.” longer influences the vertical movement of electrons Another research group exploiting an unusual crys- and holes towards each other. “Semi-polar” substrates tal orientation with advantageous polarization is are cut somewhere in between, where the effect of the at the Japanese firm Sumitomo Electric. In 2009 its polarization field is still there to some extent. “The big research ers took the lead in the race for green, by breakthrough for us came in late 2006 when we were demonstrating 520 nm lasers. However, that title has able to get high-quality non-polar and semi-polar sub- now been reclaimed by a spin-out company estab- strates,” explains Speck. Using non-polar substrates, lished by Speck, Nakamura and fellow UCSB re - Speck and co-workers were able to achieve a wave- searcher Steven DenBaars called Kaai, which is set length of 492 nm – almost, but not quite, green. to move into production with its non-polar/semi-polar But researchers have differing opinions about which approach. Kaai reported a 9 mW continuous-wave cut is best. Strauß, for example, is not convinced that 523 nm laser at this year’s Photonics West conference. non-polar substrates are definitely the best way to pro- Regardless of these achievements, Strauß points out duce green lasers. “I don’t know whether the polar- that projector makers need green laser diodes with ization field is really the major problem,” he says. “It’s power outputs of at least 50 mW. While Kaai aims to more than 50% a question of material quality.” He demonstrate this at wavelengths above 520 nm later Projector explains that because non-polar substrates lose the this year, Strauß notes that this does not mean that the makers need band-gap-narrowing effect of polarization, the amount devices will be widely available immediately thereafter. green laser of indium used must be increased further, making the “To get high yields and to get stable high-volume pro- diodes with crystals harder to grow. Rather than increasing the duction so that the customer is satisfied will take some indium content quite so much to achieve green wave- additional time,” he says. “The race is open, and we do power outputs lengths, Strauß says that keeping quantum wells thin not know which laser will be the first, or which will be of at least makes it possible to minimize the electromagnetic the best.” 50 mW 45 Physics World May 2010

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Untitled-6 1 20/4/10 10:55:05 physicsworld.com The laser at 50: Attosecond lasers and beyond Beyond ultrafast As pulsed lasers are developed to resolve dynamics occurring on ever smaller time and length scales, Adrian Cavalieri reviews the laser technology that has enabled us to directly observe incredibly fast processes, in fields ranging from atomic physics to molecular biology Thorsten Naeser, Max Planck Institute of Quantum Optics

Since the first days of the ruby laser 50 years ago, laser occur on the sub-picosecond (10–12 s) or femtosecond Adrian Cavalieri is a systems have steadily improved thanks to advances in (10–15 s) timescale. However, the phrase has now be- professor of physics laser gain media and mirror technology. On the one come essentially outdated, as processes on the attosec- at the University of hand, incredibly powerful lasers have been developed ond (10–18 s or 1 as) timescale – 1000 times shorter than Hamburg, Germany, for fusion research that are able to deliver huge pulses a femtosecond – are now accessible (see box on page and head of a research group at the of energy to their targets, resulting in local environ- 51). Indeed, attosecond spectroscopy could lead to the Max Planck Research ments similar to the interior of the Sun; on the other, ability to directly observe charge transfer in photo- Department for we now have lasers that can precisely deliver ultrashort voltaic cells and transistors, for example, allowing Structural Dynamics pulses of energy to atomic, molecular and condensed- researchers to understand precisely how the electrons within the Center for matter systems to trigger various physical processes and move around such devices. This knowledge could help Free-Electron Laser to measure their instantaneous characteristics. us to create photovoltaic cells that are more efficient, Science, e-mail The term “ultrafast” was originally coined in 1982 to and transistors that switch faster, both of which would adrian.cavalieri@ describe dynamical processes observed with lasers that impact on our daily lives. mpsd.cfel.de 47 Physics World May 2010 The laser at 50: Attosecond lasers and beyond physicsworld.com

1 Four-level picture shutter speed or the duration of the flash, ultrafast time-resolved studies on the femtosecond and now level 4 attosecond timescale are generally bound by the dur- decay ation of the laser pulse. In ultrafast, time-resolved “pump–probe” experiments, a first pulse, called the upper lasing state (level 3) “pump pulse”, is used to trigger a dynamic process, while a second subsequent pulse, called the “probe low-frequency, pulse”, is used to observe the system a short period of pump long-wavelength photon time later. Today, we can access the attosecond regime, photon with the production of laser pulses as short as 80 as. high-frequency, short-wavelength photon Hand in hand with pulsed lasers is the field of non- linear optics. Typically, when light passes through a lower lasing state (level 2) transparent material, the polarization of the material – the distribution of positive ions and electrons – is decay affected proportionally (or almost) to the intensity of ground state the incident light, i.e. the optics are linear. However, (level 1) any deviation from a truly proportional response re- The lasing media used for pulsed lasers allow lasing transitions with a large range of energies, sults in nonlinear effects that can become significant if which thus emit photons with a large range of frequencies. Here, the laser gain material – a the light propagates through a very thick material or doped crystal – is “pumped” by photons from an excitation source, such as a very bright white through a long fibre-optic cable, for example. But flashed lamp or another laser, specifically tuned to the pump transition energy. Absorbed rather than using low-intensity light and very thick or “pump” photons transfer their energy to electrons in the ground state (level 1), exciting them to a long materials, nonlinear effects can also be studied higher energy (level 4). Next, through a decay process such as a vibration, the electrons relax using thinner materials and a very intense, coherent into the upper lasing state (level 3). When the electron population in level 3 is greater than that laser beam. Thus the field of nonlinear optics began in level 2, the lower lasing state, a “population inversion” is said to exist and the conditions are shortly after the invention of the laser in 1960. set for stimulated emission. When an electron decays from level 3 to level 2, a photon is Indeed, only a year later, researchers at the University emitted, which, if a population inversion exists, can “stimulate” another electron in level 3 to of Michigan showed that laser light could be doubled in decay to level 2, emitting a second photon, and so on. The stimulated photons are emitted in the frequency when fired into a normally transparent quartz same direction and in phase with the first, resulting in the emission of coherent laser radiation. crystal. Since then, we have taken advantage of our understanding of this “second-harmonic generation”, Pump it up and other nonlinear processes, and fed-back the know- While some lasers operate in a continuous-wave mode, ledge into the design of pulsed lasers. Coming full cir- emitting radiation with nearly a single monochromatic cle, nonlinear effects are now inherent in nearly every frequency, pulsed lasers emit radiation over a broad step of creating a laser pulse, and present a promising range of frequencies – billions in fact. These frequency route to the next generation of laser technology. components are timed exactly so that their electric fields nearly cancel each other out, except for during one tiny Sapphire to start period of time when they combine constructively in one One of the first steps towards attosecond pulsed lasers intense pulse. So when we refer to a pulsed laser, there occurred in 1981 with the demonstration of titanium- is no mechanical shutter controlling when the light is doped sapphire, or Ti:sapphire, as a suitable broadband emitted; rather, the pulse is created by coherent radi - laser gain crystal by Peter Moulton at the Massachusetts ation with many different frequencies interfering. Institute of Technology. Ti:sapphire is unique in that The frequencies of light that exist in a laser’s resonant when it is pumped by a continuous-wave laser, a huge cavity are determined by two factors. First, they depend range of lasing transitions can occur. While the laser on the lasing transitions that occur in the laser gain that pumps the Ti:sapphire is narrowband, i.e. nearly medium. In pulsed lasers, a gain material is chosen that monochromatic, Ti:sapphire emits over a range of fre- has many different lasing transitions (figure 1). Second, quencies and is broadband. From Heisenberg’s energy– the cavity dimensions only allow light frequencies for time uncertainly principle, ΔEΔt ≥ h– /2, a broad band- which the electric field has nodes at the cavity’s end width of laser energies, or frequencies, is required to mirrors. With the right material and cavity it is possi- produce a short pulse of laser light: the greater the ble for billions of frequencies to lase simultaneously bandwidth, the shorter the pulse. and generate a short pulse (figure 2). Pumped by a laser with a wavelength of approxi- Because they alternate between a short burst of emis- mately 530 nm, Ti:sapphire emits light with wave- sion known as the “pulse” and a much longer downtime lengths from about 600–900 nm (orange to infrared). in between, pulsed lasers can produce high peak But while a broad range of colours, or frequencies, are powers: since power is energy per unit time, compres- produced, a pulse is not created without some further sing a fixed amount of energy into a shorter time inter- intervention. What is needed is for the laser frequen- val results in a higher peak power. Using the 103–104 W cies to be in phase at some point in the cavity. of power from a standard wall socket, for example, Forcing the various frequencies into phase is lasers can easily produce pulses with terawatt (1012 W) achieved through a process known as “mode locking”. peak powers – but only for a few millionths of a bil- The laser pulse then exists at the dynamic point in space lionth of a second. at which the many frequencies are in phase with each As in stroboscopic photography, where the fastest other. This “point of coincidence” moves back and motion that can be captured is defined by the camera forth in the cavity at the speed of light, as the phase 48 Physics World May 2010 physicsworld.com The laser at 50: Attosecond lasers and beyond

2 Constructive interference 3 Near-single-cycle optical pulse electric field (arbitrary units) electric field (arbitrary units)

–20 –15 –10 –5 0 5 10 15 20 0–2–4–6–8–10 42 6 810 time (fs) time (fs) Frequencies that are in phase sum to produce a pulse. The bottom This figure shows a simulated near-single-cycle laser pulse, which is curve (red) is a sum over the four representative curves shown in blue, nearly the shortest optical pulse that can be generated. The “drive as well as about 500 others with frequencies in between. The pulse” envelope (black) simply characterizes the pulse and is an top-most blue sine wave shows the highest frequency component and artificial construct. The light’s carrier electric field (red) drives the bottom-most wave shows the lowest. The electric fields of the physical phenomena. The real pulse results from constructive different light beams are in phase and interfere constructively at one interference of a broad band of frequency components. This optical moment in time, before falling off quickly and just about cancelling pulse needs to be converted to extreme-ultraviolet radiation to create out until the next in-phase moment a relatively long time later. an attosecond pulse. velocity and group velocity of light are nearly identical not yet in the attosecond regime. in air. Each time the pulse passes the “output coupler” Because light pulses cannot be shorter than one oscil- where the laser light leaves the cavity, which can be lation of the carrier electric field, or the light’s wave- thought of as an imperfect mirror, a portion of the pulse length, the shortest pulse that Ti:sapphire could emit is emitted. The emitted light appears as pulses sep- for light pulses centred on 750 nm, or near-infrared arated by the cavity round-trip time. Today’s most (NIR), is 2.5 fs. Evidently, attosecond laser pulses must advanced Ti:sapphire oscillators emit optical pulses be composed of shorter wavelengths, equivalent to lasting about 5 fs – barely a few cycles of the electric using photons with higher energies. For pulses shorter field and near the fundamental limit. Maxwell’s equa- than 100 as, this requires the light to be in the extreme tions of electrodynamics tell us that the shortest pulse ultraviolet (XUV) range, where typical photons have of light that can ever be generated is equal to a single a wavelength and energy of about 12 nm and 100 eV, cycle of the carrier electric field (figure 3). respectively. Converting the Ti:sapphire NIR photons (at about 1.6 eV) to XUV photons (at 100 eV) requires Chirping and harmony a significant energy boost. The NIR pulses are con- To generate shorter, attosecond pulses, the laser light verted into attosecond XUV pulses through a process must be shifted to shorter wavelengths. But before this known as “high-order harmonic generation” (HHG) conversion can be achieved, the pulses need to be (figure 4). Today, using this method, the shortest pulses much more energetic and so are amplified in energy are 80 as in duration. from several nanojoules to the millijoule level. So as There can be up to 108 photons in the attosecond not to damage the crystal used to amplify the energy, pulse; but while this sounds like a lot, it is not enough “chirped-pulse amplification” – first demonstrated by to be split into the two pulses required for standard Gerard Mourou at the University of Rochester in 1985 pump– probe experiments and also obtain a good – is employed, where the pulses are stretched in time enough signal-to-noise ratio to measure anything. If to as long as a nanosecond by “de-phasing” their fre- there were enough photons to do such experiments, quency components to reduce the peak intensity of the time resolution would be limited only by the atto- the pulse. Fol lowing amplification, the pulses are second pulse duration, as is the case in more standard recompressed in time by putting the frequency com- ponents back in phase. Next, the amplified pulse is Today’s most advanced Ti:sapphire shortened using a spectral broadening and pulse-time compression stage, which uses nonlinear effects in a noble gas and dispersive mirrors that correct for oscillators emit optical pulses additional de-phasing in the broadening process. Cur- rently, the most advanced Ti:sapphire amplifier sys- lasting about five femtoseconds – tems utilizing all of these components can produce optical pulses as short as 3.3 fs with up to half a milli- barely a few cycles of the electric joule of energy. So now we have laser pulses that have much more energy than when we started but are still field and near the fundamental limit 49 Physics World May 2010 The laser at 50: Attosecond lasers and beyond physicsworld.com

4 From infrared to extreme ultraviolet 1000 XUV filter

0 0 potential energy potential energy intensity (counts)

0 0 0 90 100 110 120 130 140 radial co-ordinate radial co-ordinate photon energy (eV) Creating attosecond pulses requires a process known as “high-order harmonic generation”, in which near-infrared laser pulses are shone into an inert gas jet. The electrons in the gas atoms, originally in an unperturbed atomic well (dotted black line), see a different potential (red) when the laser electric field (solid black line) perturbs the potential. What happens is that the laser electric field folds down the potential of the atomic well (left), increasing the probability that an electron will escape by tunnelling through the barrier and be accelerated away from its parent ion by the same electric field. When the oscillating electric field changes its sign (which happens every half-cycle), the electron’s direction of travel is reversed and it is accelerated back towards its parent atom. The electron then recombines with its parent atom (middle) and releases the kinetic energy that it gained while being accelerated in the form of a high-energy, extreme-ultraviolet (XUV) photon. Many electrons take part in this process on each half-cycle of the driving laser field and the result is a broad distribution of kinetic energies at recombination and a corresponding broad band of XUV emission. In the shortest drive laser pulses there are only a few half-cycles of the carrier electric field. At lower XUV photon energies, these photons interfere with each other, resulting in a spiked structure in the measured spectrum (right). In contrast, the highest energy photons are emitted in a single burst, by the electric-field oscillation with the largest amplitude, resulting in an interference-free, smooth drop-off at the highest photon energies. A filter is used to let through only those photons with high energies and a smooth spectrum, resulting in an isolated attosecond XUV pulse.

fem to second pump– probe experiments. Cur rently, in same property is also exploited in laser eye surgery. attosecond spectroscopy only a single attosecond pulse Originally discovered through an unfortunate laser eye and the NIR drive pulse are available. Nevertheless, injury, ultrafast laser pulses can deliver the precise attosecond resolution can still be achieved using a amount of energy required to break protein bonds in measurement technique now called the “attosecond the eye without affecting the surrounding tissue. transient recorder”. The attosecond pulse is used to Attosecond laser pulses, which are not only short but trigger the dynamics, while a much weaker replica of are also composed of high-energy photons, can be used the drive-pulse electric field is used as a probe. The to study inner-shell atomic processes including relax- attosecond transient recorder was first demonstrated ation following ionization by energetic photons. The by Ferenc Krausz and co-workers at the Technical study of these processes may be highly relevant to our University of Vienna, Austria, in 2004 and has since understanding of how human cells become malignant been the basis for many measurements made in and cancers develop. attosecond spectroscopy. In 2007 attosecond pulses were used by Krausz and colleagues to probe one of the fastest distinct events What we gain yet recorded in the time domain. The researchers were Ultrafast lasers have been widely used in industry for able to use attosecond spectroscopy to observe the micromachining parts, as no material can withstand individual elementary steps of photoemission – the the intensity of a femtosecond laser pulse. Since only a process by which electrons are emitted from a mater- small amount of energy is used to reach these high in - ial by light – namely excitation, transport and emission. tensities, only a tiny amount of material is removed with In fact, electrons from the delocalized conduction- each pulse, allowing for high-precision cutting. This band states were found to be emitted approximately 100 as before the electrons from localized, deeply bound core states. It is not yet precisely clear why such Attosecond laser pulses can a delayed emission exists, but as photoemission is one of the most fundamental examples of quantum me- be used to study atomic processes chanics, experiments will continue until full under- standing has been gained. that may be highly relevant to Fast forward There is a lot we can do with attosecond laser technol- our understanding of how ogy, but to make progress, such systems need to be used more widely. With their extremely short but rel- human cells become malignant and atively weak pulses, attosecond laser systems comple- ment large-scale “hard” (high photon energy) laser cancers develop facilities, such as the Linac Coherent Light Source at 50 Physics World May 2010 physicsworld.com The laser at 50: Attosecond lasers and beyond

Grasping timescales

one optical cycle (~2.5 femtoseconds) Eleftherios Goulielmakis Thorsten Naeser, Max Planck Institute of Quantum Optics

As laser performance improves, the quantities that define it sound ever Getting shorter, the femtosecond regime is the characteristic timescale more impressive, with each successive prefix more exotic than the last. For on which chemical reactions take place, or the time required for bonds power, the numbers become increasingly large – gigawatt (109 W), between atoms and molecules to be broken and formed. Observing this in terawatt (1012 W) and petawatt (1015 W). Pulses, however, are getting ever real time has been called the “holy grail” of chemistry, letting us study shorter – picosecond (10–12 s), femtosecond (10–15 s) and attosecond everything from the storage and release of energy in batteries to the (10–18 s). It is these short pulses from ultrafast lasers that are now letting fundamental process of photosynthesis. us explore processes on these timescales in real time. And finally to the timescale that is the most recent barrier broken by But these quantities can remain abstract, as it is difficult to relate them pulsed lasers: the attosecond. On the attosecond timescale, even the to anything in our daily lives. One second is a quantity with palpable making and breaking of chemical bonds appear to occur slowly, and would meaning, as it is roughly the time between beats of the human heart and is be akin to watching a slow-motion nature video of shoots unfurling their an interval that we can easily perceive. A picosecond, in contrast, is the leaves. In this regime, we are able to resolve charge dynamics – the characteristic time taken for molecules to move back and forth. We are movement of electrons between the energy levels of an atom, or of actually able to sense these motions without any fancy instruments, as they electrons or holes (electron counterparts) through an insulating interface are responsible for the temperature of the air and everyday objects. such as a p–n junction in a transistor. the SLAC National Accelerator Laboratory in the US cycle optical light pulses, which is not possible in today’s and the European XFEL currently under construction chirped-pulse amplification systems. in Germany. OPAs can also be used to create HHG drive pulses As attosecond laser systems improve, they will let us with different carrier wavelengths. The maximum pho- access ever more complex systems and dynamics. In ton energy that can result from the HHG process most experiments, a system can be prepared, its dy- depends on the amount of kinetic energy that the ion- namics triggered and subsequently observed every few ized electron can accumulate while being accelerated in microseconds on a fresh sample to build up measure- the carrier laser field. The longer the electron travels ment statistics. Therefore, ideally, attosecond lasers in the electric field, the more kinetic energy it has time would pulse much faster at repetition rates higher than to amass, and the greater the emitted photon energy. those that are currently possible. However, increasing This interaction time can be increased by using longer- the repetition rate of current attosecond laser systems wavelength drive pulses. By moving to longer wave- is impossible owing to the heating that this causes in length, ultrashort drive pulses, the photon energy of conventional laser gain media. isolated attosecond XUV pulses can be increased, thus In the future, it will be possible to use nonlinear optics allowing the efficient generation of pulses deeper in to move beyond the limits of standard laser gain media the XUV or even in the “soft” (or low energy) X-ray in attosecond lasers. In a process called parametric regime. This is critical, as carbon absorbs XUV radi- amplification, the nonlinear response of certain trans- ation at 284 eV making it visible, while water remains parent crystals can be used to couple energy from one transparent, allowing researchers to probe deep inside frequency of light to another. For femtosecond pulses, organic materials with attosecond resolution on atomic parametric amplification can be used to transfer light length scales. from a single frequency into a broad band of other fre- Looking further ahead, the development of a tech- quencies, as is the case in Ti:sapphire. How ever, in con- nique called “quasi-phase-matching” may lead to atto - trast to traditional laser systems, during parametric second light sources producing hard X-ray photon amplification light is not strongly absorbed, so heating energies and orders of magnitude more photons per is no longer a problem, allowing higher pulse repetition pulse, which would allow these sources to compete with rates and average powers. The average power output large-scale facilities. It has been predicted that the of optical parametric amplifier (OPA) systems could be bandwidth of emission will also increase substantially, increased to kilowatt levels. Further more, it is possible allowing for the generation of sub-attosecond, that is to achieve even higher gain bandwidths in parametric zeptosecond (10–21 s), pulses, at which point it would amplifiers that allow direct amplification of quasi-few- be safe to say that we have gone beyond ultrafast. ■ 51 Physics World May 2010 HV Angle or Inline Valve with electromagnetic actuator

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Where next for the laser? From sharpening astronomical images and searching for gravitational waves to creating Bose–Einstein condensates and measuring the properties of DNA, the laser has had a tremendous impact on many different areas of science. Here, six experts recall how the laser has advanced their fields of interest – and speculate where the laser will take these areas next

Astronomy turbulence is changing all the time, these dium, creating a guide star at an altitude of Claire Max is an astronomer measurements and corrections must be done about 95 km by exciting naturally occurring and director of the Center hundreds of times a second. sodium atoms in the Earth’s upper atmo- for Adaptive Optics at the Early adaptive-optics systems used light sphere. The second type is tuned to green or University of California, from a bright star to measure the turbulence. even ultraviolet wavelengths and uses Ray- Santa Cruz, US However, most objects of astronomical in- leigh scattering of atmospheric molecules We all know that turbulence in terest do not have bright stars sufficiently and particulates to create a guide star at the atmosphere makes stars twinkle, but it also close by, and hence the sky coverage of ad- an altitude of 15–20km. The advantage of severely blurs telescope images. Newton real- aptive optics was quite limited. Then, in the green and ultraviolet lasers is that they are ized this back in 1730, when he wrote in Opticks early 1980s, astronomers realized that they commercially available, making them much that “the Air through which we look upon the could use a laser to make an artificial “star” cheaper to use than adaptive-optics systems Stars, is in perpetual Tremor… The only Rem - as a substitute. This insight greatly extended that exploit yellow light. edy is a most serene and quiet Air, such as may the reach of adaptive-optics systems, since Thanks to laser guide-star adaptive optics, perhaps be found on the tops of the highest lasers could be pointed in the direction of today’s 8–10 m telescopes have better spatial Mountains above the Grosser Clouds”. any observing target in the sky. In the past resolution at infrared observing wavelengths Theoretically, telescopes of ever larger five years these laser “guide star” adaptive- than the Hubble Space Telescope, simply diameter should be able to resolve ever optics systems have really come to fruition, because of the larger size of their mirrors. smaller features within astronomical images. to the point where today every major 8–10 m Proposed giant telescopes, such as the Thirty But the blurring due to atmospheric turbu- telescope sports its own laser beacon. Meter Telescope, the Giant Magellan Tele- lence is so severe that even today’s largest The lasers used in these beacons have re - scope and the European Extremely Large ground-based telescopes (8–10 m in diam- spectable average powers of about 5–15W Telescope, all plan to use multiple laser guide eter) cannot see any more clearly than the (a typical laser pointer, in contrast, has a stars at the same time. This will allow astron- small 20 cm backyard telescopes used by power of less than 1 mW). Indeed, federal omers to measure, and correct for, the tur- amateur astronomers on weekend evenings. regulations require US observatories to turn bulence in the entire 3D column of air above To remedy this situation, astronomers have them off whenever aircraft approach; obser- the telescope. These multiple-laser systems turned to adaptive optics, a technology that vatories also file their observing plans in will use the techniques of tomography – sim- measures snapshots of the atmospheric tur- advance with Space Command to avoid hit- ilar to those used in medical imaging’s com- bulence and then corrects for the resulting ting sensitive space assets. puterized axial tomography (CAT) scans – to optical distortion using a special deformable Two types of laser predominate. The first is reconstruct the turbulence profile, enabling mirror (usually a small mirror placed behind a custom-built system that is tuned to the yel- adaptive-optics correction over much wider the main mirror of the telescope). Since the low 589 nm resonance line of neutral so- fields of view than are available today. 53 Physics World May 2010 The laser at 50: Visions of the future physicsworld.com

Atomic physics William D Phillips is a New kinds of lasers with different physicist at the National Institute of Standards and wavelengths, ever shorter pulse lengths, Technology (NIST) in Gaithersburg, Maryland, US. He shared the 1997 Nobel ever higher powers, ever narrower spectral Prize for Physics with Claude Cohen- Tannoudji and Steven Chu for cooling and widths and ever better stability have all trapping atoms with laser light In the early 1970s I was a young graduate stu- made possible new kinds of experiments dent in Dan Kleppner’s research group at the Massachusetts Institute of Technology, William D Phillips working on a thesis that involved making precision measurements with a high-mag- ter stability have all made possible new kinds such as DNA. Then we can use optical netic-field hydrogen maser (masers were the of experiments. Laser cooling of many more tweezers and optical traps to “hold onto” microwave precursors to the laser, which was types of atoms and ions, plus giant cold these beads and exert very tiny, controlled originally called an “optical maser”). Klep- molecules, atomic clocks ticking at optical forces on the DNA molecules. pner and Norman Ramsey had invented frequencies, and non-classical states of light The lasers that we use for this have some a low-field version of the hydrogen maser are just some of the paths into which lasers pretty extraordinary properties – they are more than a decade earlier, and the high- have led atomic, molecular and optical not like the laser in a laser pointer or in your field version was producing unprecedentedly (AMO) physics. CD player. We need to be able to hold a laser accurate measurements of magnetic mo- Moreover, lasers have allowed AMO phy- beam stably in space to within the diameter ments in atoms – a sort of zenith for this kind sicists to realize Bose–Einstein condensa- of a hydrogen atom, or about 1 Å, for several of atomic physics. tion, to create optical lattices and to study seconds at a time. This is because the base But then came a new development that ultracold Fermi gases. Each of these has pairs in a DNA molecule are only separated would change the direction of work in Dan’s deepened the connections between AMO by about 3.5 Å, and one of the things we are lab, in my career and in atomic physics as a and condensed-matter physics. It may be interested in studying is how the enzyme whole: the first continuous-wave, commer- that lasers and cold atoms will help to eluci- RNA-polymerase, which “reads” the genetic cial, tunable dye lasers. The lasing medium date some of the outstanding problems in code, moves as it climbs the DNA ladder one in these devices was an organic dye that lased condensed matter, such as the origins of base pair at a time. over a far wider range of wavelengths than, high-temperature superconductivity and the It is amazing that we can literally watch this for example, a helium–neon laser, where nature of fractional-quantum-Hall states happen, and it all depends on being able to the gain medium is an atomic gas. The intro- that are useful for quantum computing. shine laser light on the enzyme, scatter that duction of these devices meant that even Ever since they first became available, light and measure displacements that are those who were not experts in laser design lasers have invigorated and reinvigorated accurate down to an angstrom. We are con- and construction could, by tuning a laser to atomic physics, and the adventure shows no stantly looking for lasers with higher power an atomic-resonance transition, explore a signs of stopping. in single modes and better stability prop - new domain of atomic manipulation where erties. Some of the new generation of diode coherent light was the key tool. Biophysics lasers are now reaching the point where they Eager to play with these new toys, I asked Steven Block is a can be used for these experi ments, but for the Dan to suggest an additional thesis experi- biophysicist at Stanford most part they have not made it out of the lab ment using lasers. He agreed, and suggested University, California, US yet. It will be very interesting once they do. that I study collisions of optically excited Over the past 10 years, it has sodium atoms. I began to build the appar- become possible to do ex - Defence atus. Other students and postdocs in the periments in biophysics that Jeff Hecht is a freelance group started new experiments as well. Each were previously just pipe dreams. For ex - science and technology issue of the research journals brought an ample, I work in a field known as single mo - writer based in Auburndale, increasing number of laser-related papers, lecule biophysics. In this area, the challenge Massachusetts, US, who and each conference saw reports of new is to study the molecules of life – the proteins, has covered laser weapons laser experiments. nucleic acids, carbohydrates and other chem- since 1980 The excitement of that time was palpable. icals that make us up – literally one molecule High-energy laser weapons – long the stuff New ideas and new experiments popped up at a time. This is not easy to do, because all of science fiction – have recently reached a everywhere. In 1978 I was inspired by Dave biomolecules are much too small to be seen turning point. But it is not the one you would Wineland’s demonstration of laser cooling using, say, a conventional microscope. None- expect if you saw news clips of a laser-armed of ions at the National Bureau of Standards theless, we are finding that they can be Boeing 747 shooting down a target missile in (now NIST) in Boulder, Colorado, and by manipulated and measured, and the tech- February this year. Instead, the US military is an idea from Art Ashkin at Bell Laboratories niques that are involved in doing this often planning to concentrate on thwarting attacks to slow and trap a beam of sodium atoms. require lasers. from short-range targets such as rockets, Later that year, when I went to the bureau’s One technique that my lab has helped to mortars and artillery shells. labs in Gaithersburg, Maryland, I took my pioneer is known as “optical tweezers”. The Modern laser weaponry dates from about thesis apparatus with me and began to work idea behind optical tweezers is that you can 1980, when the main goal was to develop on laser cooling and trapping of sodium. use the radiation pressure supplied by an high-energy lasers capable of destroying For me, the excitement I felt in the 1970s infrared laser beam to capture and manipu- missiles launched hundreds or thousands in Dan’s lab has never waned. New kinds late small materials – including individual of kilometres away. Indeed, US President of lasers with different wavelengths, ever proteins and nucleic acids – and move them Ronald Reagan’s “Star Wars” programme shorter pulse lengths, ever higher powers, around under a microscope. To do this, we spent billions on plans for orbiting laser bat- ever narrower spectral widths and ever bet- hook tiny microscopic beads up to molecules tle stations. But tough technology problems 54 Physics World May 2010 physicsworld.com The laser at 50: Visions of the future and the end of the Cold War changed the re- Bagging a few test rockets should be easy. cessfully demonstrated the first optical- quirements. The result was the Air borne Engineering mobile lasers that work reliably wavelength FEL amplifiers and oscillators Laser (ABL): a Boeing 747 equipped with a in messy places where people are shooting in 1974 and 1976, respectively. The focus megawatt chemical oxygen–iodine laser and at them is a much tougher problem. We will since then has been on using FELs to do designed to shoot down missiles launched probably see prototypes blasting targets out things that are tricky to pull off by other by a “rogue state”. of the sky within a few years, but do not ex- means. Perhaps the best known application But in May 2009, US defence secretary pect battlefield deployment until the 2020s is to generate tunable, high peak power, Robert Gates reported that the ABL (long at the earliest. coherent, femtosecond X-ray pulses at ener- plagued by budget and deadline overruns) gies above 1 keV to carry out time-resolved had a lethal range of less than 140 km – far Free-electron lasers structural and functional studies of complex short of the planned minimum of 200 km. So, John Madey is director of individual and interacting molecules. The after the current round of tests (conducted the FEL Laboratory at the first such X-ray FEL is now in operation at at an undisclosed shorter range), efforts to University of Hawaii, US, the SLAC National Accelerator Laboratory reach megawatt powers will start again with and contributed to the in the US, with the European X-ray Free- lasers that use diode-pumped alkali-metal Honolulu Star Bulletin development of free- Electron Laser due to come online at the vapours. Lasers of this type currently emit electron lasers DESY lab in Germany in 2014. just tens of watts but may eventually offer a Like all lasers, free-electron lasers (FELs) Even for applications where other types of better power-to-size ratio than the ABL. rely on the principle of stimulated emission lasers might be adequate, the big advantage Until those plans get off the ground – if to amplify a beam of light as it passes through of FELs is that they are so flexible. FELs they ever do – the bold new future of laser a region of space. In other words, as elec- have therefore proved invaluable in carrying weapons will be solid-state lasers that emit trons move from a high- to a low-energy out exploratory research when the require- 100 kW or more in a steady or repetitively state, they emit photons of light all at the ments of a particular application have not yet pulsed beam. It has already been demon- same wavelength and all moving in the same been determined or when a research team strated that kilowatt-class lasers can detonate direction. But unlike the transitions between does not have the time or money to develop unexploded ordnance left on the battlefield bound electronic states in other lasers, FELs a new specialized laser system needed to sup- by illuminating it from a safe distance. The exploit another of Einstein’s key discoveries port the application. The short-pulse, high- hope is that lasers in the 100–400 kW range – special relativity – to provide tunable elec- peak-power, third-generation FELs, which could also destroy rockets, mortars and shells tromagnetic radiation from a beam of rela- were pioneered in the 1980s, have been at distances of up to a few kilometres. The tivistic free electrons as they move through partic ularly useful for developing new surgi- close range of these targets would greatly a spatially periodic transverse magnetic field. cal techniques and for exploring the energy ease beam-propagation problems that ham- According to special relativity, the elec- levels, band structure and mobility of elec- per laser-based missile-defence systems. trons perceive such a field as an intense trons and holes in new electronic and optical Moreover, by detonating explosives in the air travelling wave in their rest frame, with a materials, without having to worry about with laser heating, rather than firing pro- wavelength reduced in proportion to their longer probing laser pulses damaging the jectiles at them, laser-based weapons could kinetic energy. Photons scattered by the elec- material. reduce “collateral damage” to friendly sol- trons from this pulse in the direction of their The more recently developed high-aver- diers and non-combatants. motion are reduced in wavelength once again age-power FEL systems have extended these In March 2009 US defence giant Northrop when viewed from the laboratory frame. As capabilities to include research on possible Grumman reported continuous emission of a result, electrons with a kinetic energy of laser applications for industrial-scale ma - more than 100 kW for five minutes from a 50 MeV emit near-infrared radi ation when terials processing. Of at least equal signi- laboratory diode-pumped laser. This Feb - moving through a field with a period of 2 cm. ficance are the improvements in remote ruary, Textron Systems reached the same Light of longer and shorter wavelengths can sensing for climate-change research made goal with its own design. These are by far the be created by simply varying the energy of possible by the broad tunability, high peak highest continuous powers achieved in a the electrons. FELs can readily provide laser power, and exceptional spatial and temporal solid-state laser. The next step will be to light with about 1% of the instantaneous coherence offered by FELs at visible and engineer a 100 kW laser that works on ships, power of the electron beam – megawatts or infrared wavelengths. trucks and planes. The US Army is moving more – and their pulse lengths can vary from There are, however, a few clouds on the Northrop Grumman’s device to the High less than a picosecond to full continuous- horizon for FEL research. Historically, such Energy Laser System Test Facility at the wave operation. Excep tional phase coher- research has mainly taken place at a handful White Sands Missile Range, New Mexico, ence is also attainable through the use of of small and mid-sized university and gov- where it is planning to try out a mobile ver- suitable interferometric resonator systems. ernment labs in the US, Europe and Asia. A sion installed in a heavy battlefield truck. An - Serious efforts to explore the possible recent transition to larger national labs has other defence agency, DARPA, is building a applications of FELs began shortly after brought many scientific advances, but also lightweight 150 kW solid-state laser for use colleagues and I at Stanford University suc- runs the risk of making both the science and in fighter planes, while the US Navy is plan- ning tests of similar lasers at sea. The lasers used in all these projects mark Short-pulse, high-peak-power, a radical departure in laser-weapon design. Earlier weapon-class lasers were chemically third-generation free-electron lasers have fuelled, but commanders did not want them on the battlefield because handling chem- ical fuels posed major logistical issues. They been particularly useful for developing also wanted lasers that could be powered by diesel generators. But other formidable new surgical techniques and for exploring challenges remain, including damage to the laser itself, the need to operate in a dirty bat- new electronic and optical materials tlefield environment and the expected high cost of the devices. John Madey 55 Physics World May 2010 physicsworld.com

the technology less accessible to university periments were between one and a few tens scientists, who may be based far away from of metres in size and used argon-ion lasers, large central facilities. It will, therefore, be which operate at a wavelength of 514 nm and critical to ensure that the customer and sup- output several watts of power. Such inter- port base for the technology remains aware ferometers were usually designed to study of the FEL’s smaller-scale applications, not specific problems in gravitational-wave in- just the signature high-power and short- terferometry, such as comparing different wavelength ones. optical configurations, finding ways to con- Finally, there are concerns that the sup- trol the suspended optics and characterize pliers of FEL-supporting technologies – in - noise in subsystems such as mirrors, and de - cluding high-power microwave, ultra-high veloping length and alignment control sig- vacuum and special optical materials – may nals for the suspended optics. not be able to continue these product lines, Unfortunately, the plasma tubes used in given the decreasing industrial markets for argon-ion lasers, along with the cooling water them. Wise governments should take the they require, produce high levels of laser- steps needed to ensure that the know-how frequency noise. What is more, the relatively on which these critical national capabilities short lifetimes of these tubes made them im - rely is not lost. practical for use in an observatory. Finally, the power output of the lasers – while higher Gravitational waves than a helium–neon laser – was short of the Eric Gustafson is at the hundreds of watts that more advanced detec- California Institute of tors were understood to require, thanks to Technology, US, and leads the fact that at high frequencies the detector the instrument- science group sensitivity is limited by shot noise. of the LIGO gravitational- In the 1990s, as the current group of kilo- wave observatory metre-scale observatories (LIGO in the US, Often referred to as “ripples in space–time”, VIRGO in Italy and GEO in Germany) gravitational waves are generated during were being planned and built, diode- extremely violent astrophysical events in pumped solid-state lasers became available. which the velocities of objects such as neut - These lasers not only had much lower levels ron stars or black holes change by substan- of frequency noise than argon-ion lasers, tial fractions of the speed of light over a very but also the potential to produce much brief period of time. Detecting such waves is higher power. Initially, their maximum a challenging task because, for ground-based power output was about 10 W, but improved detectors, these changes in velocity occur on diode-pumped lasers and the use of injec- timescales between a fraction of a millisec- tion-locked power oscillators or master- ond and a few tens of milliseconds. Meas- oscillator power-amplifier configurations uring these tiny fluctuations in the curvature made 100 W-class lasers possible for a new of space–time requires the use of very sensi- generation of interferometers. These new tive laser interferometers, in which beams of interferometers will be deployed over the light travel down the perpendicular arms of next few years at LIGO and VIRGO, and the device, bounce off mirrors at the far end will use 200 W lasers. Mean while, GEO will of each arm and then return to interfere with use a squeezed-light technique to produce one another. The idea is that a passing gra - better shot-noise performance at lower vitational wave should change the interfer- laser power. For space-based instruments ence pattern in a characteristic way. such as the Laser Interferometer Space As laser technology has evolved, the lasers Antenna (LISA), diode-pumped solid-state used in gravitational-wave experiments have lasers were selected not for their high power changed with it. The first interferometric ex- potential but for their very high efficiency periment designed to detect these waves, and reliability, characteristics that are espe- built by Robert Forward at California’s cially important for a space-based mission. Hughes Research Laboratory in the early It is not clear exactly what lasers or wave- 1970s, used a 75 mW helium–neon laser and lengths will be required for future ground- was about the size of a chessboard. Forward based detectors. We may see slightly longer reached an impressive sensitivity with this wavelengths selected that can be used with device, measuring the smallest vibrational new mirror-substrate materials that are displacement that had been detected with a opaque at 1064 nm; equally well, we might laser to date: 1.3 × 10–14 m Hz–1/2 – equivalent see shorter wavelengths that allow us to use to measuring changes of less than 2 mm in thinner mirror coatings, thus reducing the the distance from the Earth to the Sun. How- thermal noise produced. It is possible that ever, the poor power-scaling properties of as researchers begin to look for the “right” the helium–neon laser meant it did not have wavelength to optimize sensitivity, we will a future in gravitational-wave interferometry find that we need wavelengths that can only beyond table-top experiments. be produced via the nonlinear frequency During the 1980s, several groups around conversion of solid-state lasers – and so our the world built interferometers in ultra-high- choice of lasers may continue to evolve. vacuum systems, with their optics suspended ■ to isolate them from ground noise. These ex- 56 Physics World May 2010 You rely on technology innovation for new tools to advance the pace and scope of your scientific discovery. Now, ITT introduces the next innovation in software technology to revolutionise the way you work with data – IDL 7.1. 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2-10_IDL_AD_PhysicsWorld_spec.indd 1 2/17/2010 5:14:46 PM physicsworld.com Careers Supporting laser science If the laser in your laboratory is not working, your first port of call (after the instruction manual!) will be someone like Harald Ellmann, whose fascination with practical problem-solving led to a career in technical support The end of the line Harald Ellmann’s job allows him to contribute to science by solving other researchers’ problems.

I first heard the phrase “a physicist can do known to me; in fact, by the time my research the reproduction quality of Blu-ray discs at anything” when I was pondering my options colleagues and I had finished our first re - mass-production sites. The customer base after I finished secondary school. But even liable diode-laser systems in the late 1990s, has broadened too: in addition to institutes after I finally decided to embark on a degree we received flyers from a start-up firm and universities, it now also spans a steadily in physics, I could not have imagined how named “TuiLaser” (which eventually be - growing range of industrial partners, with true this would be. In my case, although I came Toptica) advertising almost the same applications in materials processing, micro- started out wanting to be a scientist, physics lasers that we had just built. Thus, the job scopy and optical-storage technology. has instead led me to a career that involves requirements were an almost perfect match Despite this, the scientific market still rep- helping scientists solve problems, as the ser- with my skills, and after seven years in resents the core of Toptica’s business. One vice manager of a medium-sized laser firm, Sweden I re turned to Munich. consequence of this is that the firm is follow- Toptica Photonics. ing an “open” approach to laser design, My undergraduate studies took place Troubleshooting for physicists meaning that its customers have nearly unre- at the Ludwig-Maxmilians-Universität in When Toptica began trading in the mid- stricted access to the inner workings of their Mun ich, Germany, during the early 1990s, 1990s, its core market consisted of govern- lasers, so that they can adapt their devices to but I did my diploma thesis externally at ment institutes like the Max Planck Institute their individual needs. As a result, most of Sweden’s Stockholm University. As a mem- of Quantum Optics or the Physikalisch- my working time is dedicated to direct tech- ber of the new laser-cooling project there, Technische Bundesanstalt that were in- nical support: in other words, if someone’s my task was to set up an experiment almost volved in the rapidly evolving field of laser is not working, then I am one of the from scratch. One important aspect of this experimental quantum optics. Since then, people they call. In addition to helping trou- work was to build inexpensive diode lasers the product portfolio has expanded from bleshoot products, in quite a few cases I also and the electronics needed to control them. diode lasers to fibre lasers and optical-stor- act as an application advisor – offering sug- One year into the project it dawned on me age testers, which are devices used to check gestions on, for example, schemes for active that I had not done any real science yet. By frequency stabilization. Here it is certainly then, my aspiration was to be a scientist, and helpful to be able to tap into the vast pool of I therefore decided to take the next step by Most of my time is knowledge within Toptica: about 25% of my doing a PhD in the same research group. 85 colleagues have a PhD, predominantly in In the years that followed, however, I dis- dedicated to support: physics, and more than 50% of all employees covered that instead of being attracted to have an academic background in either phys- problems of fundamental physics, I was ics or engineering. more keen on overcoming the technical if someone’s laser The other important side of my job as “ser- hurdles that prevented the experiments vice manager” is to establish customer ser- from working. is not working, then vice as a distinct entity within the company. After I finished my PhD, I had to decide In a nutshell, this means I am working on what to do next. Fortunately, I came across I am one of the introducing structure and scalability into the an advertisement from Toptica, which was firm’s service processes so that we are pre- looking for a physicist to be its service man- pared for the ongoing growth of the com- ager. The company was certainly not un- people they call pany. We have, for example, implemented a 58 Physics World May 2010 physicsworld.com Careers

monitoring system that allows us to keep of time, in my role things tend to get blurry know even existed! track of repairs, so we always know the status rather than focused. Finding the time to In addition to these technical challenges, and the history of each product. This enables write this article, for example, required a my work requires patience, communication us to analyse our records and detect sys- combination of time management and luck: skills and empathy. It is important to remain tematic problems, and thus provide valuable I happened to encounter a relatively quiet aware of the fact that behind each technical feedback to product management and R&D. phase when my attention was not being issue there is also a real person with a prob- The next step will be to implement a ticket pulled in different – and often diametrically lem. Working in support also means that system that also keeps track of communica- opposite – directions. most often one is confronted with weak- tions with individual customers. This is some- Working in a mid-sized hi-tech company nesses and flaws in products rather than thing that will become really import ant as is a big challenge for those of us involved in strengths, and at times it can be hard to soon as the number of support employees support because the firm’s products are shoulder the collective responsibility for, exceeds the current head count of two. diverse and the cycle for innovations is short. say, a faulty laser. On the other hand, it is im- This kind of structural, long-term work In order to stay ahead of the curve commer- mensely rewarding to be able to quickly help requires a certain amount of attention and cially, the firm is constantly developing, mar- a student who has become stuck in the mid- “focus”, but my day-to-day work most often keting and selling new products. At Toptica, dle of an important experiment. So, ul - involves the exact opposite: namely, I need many of the products are customized, so we timately, I do contribute to scientific to react rather than act. There is a constant need to bring ourselves up to date all the progress – just in a rather more subtle way influx of service requests and at times my col- time. This means that very often I am con- than I had originally imagined. league and I have to juggle 10 or more of fronted with problems I have not heard of these without dropping a single one. Unlike before; in fact, there have even been a few Harald Ellmann is the service manager for in science, where one usually concentrates occasions when customers have called ask- Toptica Photonics in Graefelfing, Germany, on a certain problem for an extended period ing for help with a product that I did not e-mail [email protected]

Once a physicist: Fausto Morales Puzzle-games designer What did you do next? What are you working on now? Fausto Morales describes My eclectic academic background – an In my “day job” I am currently working as an his career as “a nomadic undergraduate physics degree, graduate work in independent consultant on decision algorithms for adventure in pursuit of physics and computer science, and finally a financial applications such as e-trading. But I am interesting problems”. doctoral programme in pure mathematics – has also progressing towards publishing two other His book Zigzagrams was allowed me to hop from one field to the next number-placement games that, like zigzagrams, published by AuthorHouse whenever I have been tempted by an interesting involve repartitioning the 9 × 9 square and in 2009 challenge. Initially, I used physics, mathematics extending the rules of Sudoku so as to provide and object-oriented computer programming to players with a wider variety of logical themes to mix Why did you decide to study physics? tackle intriguing problems for the aerospace into their reasoning processes. While reading books like Paul Davies’ The Edge of industry, such as automating aircraft route Infinity, I gradually felt the urge to explore the laws generation to maximize pilot safety in hostile What was it that sparked your interest that rule our universe. I anticipated a fascinating scenarios. Next, I worked on speech-recognition in puzzles? journey filled with beauty on both sides of the road, systems aimed at automating the interpretation of It must be innate, since I have always enjoyed and my dream came true in the late 1980s thanks messages uttered by humans, without help from solving original problems. I like chess puzzles just to the extraordinary faculty and curriculum at intervening menus. Then I moved on to develop as much as word or number puzzles, as long as they Sonoma State University in California. As an data-mining methodology, mainly for financial call for creativity. undergraduate student there, I had the rare applications, an activity that I currently juggle with opportunity to engage in serious research on logic-game design. If you could offer one piece of careers binary-star systems. Once I started doing graduate advice to physics students today, what work at the University of Michigan, this experience What are zigzagrams and how did you come would it be? enabled me to work in a high-energy-astrophysics up with them? I would say, quoting Albert Einstein, that “in research team led by James Cronin, who shared the A zigzagram is an extension of Sudoku. Each moments of crisis, only creativity is more important 1980 Nobel Prize for Physics. column and row in a zigzagram contains the than knowledge”. All physics graduates have been numbers from one to nine, but with the additional thoroughly trained to adapt to any kind of job What led you to switch to pure mathematics? condition that every compartment must contain an market – and even thrive in it – by virtue of their A superb graduate series of lectures on group odd number of odd numbers. Because the new superior ability to tackle new problems. I think that theory for physicists, taught by Karl Hecht at condition would be redundant in the familiar an open mind is the best career asset for a physics Michigan in 1990, helped me realize that I was square-box partition, zigzagrams incorporate student today. better equipped to understand and enjoy algebraic compartments of varying sizes – named ● www.zigzagrams.com structures in pure form, devoid of the complexity “zigzagons” because of their twisting appearance. introduced by their advanced applications in The rule about odd numbers introduces a new physics. By the end of the course, I concluded that I dimension into the thinking mix, enhancing the had become far more interested in groups for their “systematic search” themes of Sudoku by structural properties than for their contributions to combining them with elementary ideas that emerge theoretical physics. It was time for me to switch from the logical implications of this odd–even To make the most of your physics degree, visit gears and explore group theory. parity rule. www.brightrecruits.com

59 Physics World May 2010 Careers physicsworld.com

Careers and people

UK grants for ‘world’s best’ students physics within CNRS, France’s national exploiting the accuracy of space-borne Up to 100 research students will have their science agency. Martino, an experimental atomic clocks to pinpoint the location and fees and expenses part-funded by the UK nuclear physicist, has led the Subatech trajectory of objects on Earth. Initially government as part of a £2.5m scheme to nuclear-physics laboratory at the intended for the military, GPS devices are attract talented students from around Ecole des Mines de Nantes since 2001, and now found in numerous civilian the world to UK universities. The has also served on numerous scientific- applications, including sat-navs in cars. Newton Scholarship programme will pro- policy committees since gaining his vide £25 000 each to 100 highly doctorate in 1982. As head of the Movers and shakers skilled candidates who wish to pursue IN2P3, he will oversee operations at The CERN theorist John Ellis has postgraduate studies in the UK. With 32 laboratories (most of which are run in been appointed Clerk Maxwell median annual tuition fees reaching conjunction with universities in France) Professor of Theoretical Physics at £11 900 for overseas students on and 40 international projects, with a King’s College London. laboratory-based research courses in 2009, combined budget of about 745bn. Herbert Mook Jr of the Oak Ridge the new scholarships will not, however, He replaces the particle physicist National Laboratory has won the cover the full cost of a PhD. Nevertheless, Michel Spiro, who was elected president of Neutron Scattering Society of America’s the director of the Russell Group of elite the CERN council in December 2009. Clifford E Shull Prize. universities, Wendy Piatt, praised the The Astronomical Society of the Pacific scheme, calling it a “welcome initiative” GPS pioneer honoured has awarded its top prize, the Bruce Gold in the face of “increasingly fierce global A physicist whose method for tracking Medal for lifetime achievement in competition” for top students. The first Soviet satellites during the height of the astronomy, to Gerry Neugebarger of the Newton Scholars are expected to begin Cold War evolved into the modern California Institute of Technology. their studies in the autumn. Global Positioning System (GPS) has been The 2010 Grote Reber Gold Medal for inducted into the US National Inventors radio astronomy has been awarded to New chief for French nuclear physics Hall of Fame. Roger L Easton, who began Alan Rogers of the Massachusetts Institute Jacques Martino has been appointed his career at the Naval Research of Technology’s Haystack Observatory. director of the National Institute of Laboratory during the Second World War, Space scientist Alan Title of Lockheed Nuclear and Particle Physics (IN2P3), the was honoured for developing and testing Martin has been inducted into the umbrella group for elementary particle the concept of “time navigation”: Silicon Valley Engineering Hall of Fame. Next month

in Physics World Arizona State University Tackling cancer Efforts to understand cancer have traditionally involved viewing it in terms of chemistry and genetics. But physicists are now bringing their expertise to bear by considering living cells as mechanical objects that can be controlled

Symbols of power Theoretical physicists have long sought to describe the universe in terms of equations. Could a new class of symbols, known as adinkras, be the way forward?

Fits and starts For two years Albert Einstein blocked Theodor Kaluza from publishing what became the foundation for string theory. This, it turns out, was partly due to the human behaviour of prioritizing, which results in delays and bursts of activity

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Department of Physics Oclaro is a Tier 1 provider of innovative optical and laser components and solutions for a broad range of diverse markets, including telecommunications, industrial, Lecturer (Centre for Graphene Science) consumer electronics, medical and scientific applications. £36,715 - £43,840 per annum Headquartered in California, we enjoy global presence and As a result of winning a multimillion pound EPSRC/HEFCE Science are poised for further growth. & Innovation Award, the Universities of Bath and Exeter have established a national Centre for Graphene Science. The Centre For our R&D and manufacturing site in Zurich, we are is bringing together internationally leading research teams with looking for interdisciplinary expertise to work on: novel methods of producing, patterning and functionalising graphene; experimental and theoretical Physicists / Engineers studies of graphene-based systems; the development of new graphene-based electronic, photonic, chemical, bio- and medical to help us meet increasing demand for our products. devices and sensors. You must be able to establish an independent research programme What we look for: in graphene science that effectively interfaces with the advanced infrastructure available in Bath. This focuses on state-of-the-art s 0H$OREQUIVALENTIN0HYSICSOR/PTOELECTRONICS low temperature scanning probe-based characterisation and s +NOWLEDGEOFOPTICS LASERS OPTOELECTRONICS nanopatterning in addition to more conventional “top-down” semiconductor manufacturing, 6-sigma, RF design, nanofabrication tools. LabView. Reporting to the Head of Physics, you will play a key role within the Bath team, building on research strengths demonstrated in the last s )DEALLY PREVIOUSEXPERIENCEINSEMICONDUCTORLASER Research Assessment Exercise when the Department was ranked industry. amongst the top 5 Physics Departments in the UK. You should have a PhD in a relevant discipline and a demonstrated track record of excellence in materials-related research; experience in graphene or What we offer: other carbon-based systems is especially welcome. Researchers in the early stage of their careers are particularly encouraged to apply. s )NTERNATIONAL DYNAMICWORKENVIRONMENTWHICHALLOWS Applications should be accompanied by a 1 page outline describing you to take on responsibility from the beginning and novel research plans that would complement and enhance research in the Centre. where flat hierarchies encourage open communication. s #OMPREHENSIVEREMUNERATIONPACKAGE For further information and to apply online please visit our website at www.bath.ac.uk/jobs quoting reference JK26. Informal enquiries should be addressed to Professor Simon Bending, 0LEASESENDYOURAPPLICATIONBYEMAILTO ([email protected] or +44 (0)1225 385173). [email protected]. Closing date: 31st May 2010. Check out www.oclaro.com and find out more about us!

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Oclaro 15x2 May 2010.indd 1 19/4/10 12:33:43 Leading the way in magnet technology NMR Magnet - Project Engineer/Designer Magnex, a wholly owned subsidiary of Varian, Inc. is a successful, The applicant will be expected to demonstrate proven ability for innovation high technology company, involved in the design and manufacture of and/or product design and development, desire to work within an existing superconducting magnet systems for Magnetic Resonance and other strong team, ability to handle projects from conception to install, to work to scientific applications. deadlines and to manage a number of projects concurrently. The advertised position is a technical role, involving extensive interaction To be considered for this opportunity, please send an up-to-date CV with a with many parts of the company and some with suppliers and customers. covering letter to either [email protected], or for the attention of The applicant should be trained to at least degree level in a relevant (scientific the Human Resources Department at the address below. or engineering) discipline. A PhD and/or industrial experience would be magnex scientific ltd – the magnet technology centre: 6 Mead Road, advantageous. Some experience of magnet design, superconductors, Oxford Industrial Park, Yarnton OX5 1QU,Tel: 01865 853800 cryogenics or NMR would be of particular benefit. www.magnex.com www.varianinc.com

Physics World May 2010 PWMayClMagnexVarian7x4.indd62 1 19/4/10 12:39:49 Oxford Instruments provides high technology tools and systems for industrial and research markets, based on our ability to analyse and manipulate matter at the smallest scale. We are a global company Bell Labs, the innovation engine of Alcatel-Lucent, is a worldwide with offices and manufacturing sites in over 25 locations world-wide research and development community that focuses its efforts on key and a turnover of £200m. technologies for telecommunications. It is internationally renowned as the birthplace of modern information theory, the transistor, the laser and the Our NanoAnalysis business is a global leader in advanced analytical UNIX operating system. systems for X-ray microanalysis and electron backscatter diffraction. The growth and development of this business has resulted in some Bell Labs Ireland very exciting opportunities: Bell Labs’ research facility in Dublin, Ireland is a leading end-to-end systems and solutions lab working in the areas of thermal management, wireless sensor networks, autonomic networking, semantic data access, and services- Customer Services Business Manager centric operations research. Marketing of our international service products. Thermal Management /Eco-Sustainability Technical Manager Product Manager We have an opening for a Technical Manager to lead a research team Manage the lifecycle and product roadmap for our EDS products. working in thermal management and related eco-sustainability aspects of communication systems. The position involves the development and execution of a research programme to delivery significant energy savings in Senior Software Engineer telecommunications equipment. Developing the graphical user interfaces and software components for high technology products using C#, Visual Studio and WPF. To be considered for this position, you should have a PhD in a related area and a proven track record in research or strong industrial experience. A successful candidate will also have strong experience in crafting and To apply, please send a copy of your CV to [email protected] implementing a strategic vision for research as well as excellence in team quoting reference PWOINA1904. For more details and other excellent leadership. opportunities visit our website, To apply and to obtain, further detail on the role profile, please contact by The Business of Science. email Elena Gonzalez ([email protected]). A comprehensive benefits package exists, including relocation costs. Oxford Instruments NanoAnalysis Halifax Road, High Wycombe, See also http://www.alcatel-lucent.com/wps/portal/BellLabs/Ireland for further Bucks, HP12 3SE career opportunities and information on Bell Labs Ireland. Tel 01494 442255 www.oxford-instruments.com

Oxford_13x2.indd 1DWLRQDO*UDGXDWH 1 20/4/10 08:37:55 5HFUXLWPHQW([KLELWLRQ  -XQHs3DYLOLRQ1(&%LUPLQJKDP )ULGD\DPSP6DWXUGD\DPSP As CERN’s Large Hadron Collider opens up a new high energy frontier, the Organization is pursuing advanced research and development for an electron-positron linear collider to exploit the anticipated discoveries and further the understanding of the underlying physics. In order to lead, coordinate, and liaise the studies of both accelerator and detectors, the linear collider community at CERN is looking for a Linear Collider Studies Leader 0RUHWKDQ Your main responsibility will be to lead the linear collider work MXVWDMREVIDLU at CERN in a new project phase. You will also have a strategic international role to participate in shaping the linear collider and Visit a host of free features to help you with the fi rst step in detector landscape beyond the host Organization. Reporting directly your new life:  to the CERN Directorate and the CLIC/CTF3 collaboration board, r &9&OLQLF you will engage with other laboratories to strengthen the current collaboration. Within this framework you will drive the R&D and r $GYLFH&OLQLF prototyping work with a view to the production of a Technical r &RPSDQ\DQGFDUHHUVSUHVHQWDWLRQV Design Report. r 0RFN$VVHVVPHQW&HQWUH r 6XEVLGLVHGWUDQVSRUW  Already having extensive leadership and project management r )5((HQWU\ experience with international renown in the field of particle *Terms and conditions apply physics, you will have successfully led large collaborations requiring 5HJLVWHUQRZ FRXN interactions with both research and industry. ZZZJUDGMREV Details of the vacancy, application process and employment 6XSSRUWHGE\ ,QDVVRFLDWLRQZLWKWKHFDUHHUVVHUYLFHVRI 6SRQVRUHGE\ conditions can be found at: www.cern.ch/lcsl

Physics World May 2010 63

13x2Advert.indd 1 31/3/10 09:17:51 The Max-Born-Institute for Nonlinear Optics and Short Pulse Spectroscopy (www.mbi-berlin.de) is part of the Forschungsverbund Berlin e.V.” and is a member of the “Wissenschaftsgemeinschaft Gottfried Wilhelm Leibniz (WGL)”. In Division B: Light Matter Interaction in Intense Laser Fields (Director: Prof. Dr. W. Sandner) a position is offered for a

doctoral student in the field of experimental atomic and molecular physics. The position is immediately available for a 3-years term. The successlul applicant will work on a project funded by the “Deutsche Forschungsgemeinschaft” (DFG). The specific field of research will be the investigation of the interaction of aligned molecules with high intensity ultra-short laser pulses at large internuclear separation. Applicants should hold a university degree equivalent to the German diploma or a master degree and have good knowledge in atomic and molecular physics, ultra-short pulse laser techniques, or photo-electron/ion spectroscopy. Applications referring to the ref. no. 3-b2 should be addressed to: Dr. H. Rottke, Max-Born-Institut, Max-Born-Str. 2a, 12489 Berlin, Germany, Tel.: +49-30-6392-1370, e-mail: [email protected], preferably by e-mail.

PhD Position in Theoretical Biological Physics Untitled-5 1 19/4/10 10:50:40 Centre for Integrated Systems Biology Imperial College London Applications are invited for a PhD position at Imperial College London Faculty Search: Condensed Matter Physics, to study the quantitative aspects of sensing and signalling in various Biophysics and Quantum Optics biological contexts. Specifically, the role of cooperativity, feedback, noise, and cell mechanics in signal propagation and information processing will be The Nanyang Technological University (NTU), an excellence-driven research investigated. university in Singapore, is inviting candidates with internationally proven track records to apply for positions at the Associate or Full Professor levels in the Division For ideal candidate background and eligibility requirements, see of Physics and Applied Physics. Candidates with potential for distinction may also http://www3.imperial.ac.uk/biologicalphysics/opportunities. apply for tenure track positions at the Assistant Professor level. Send application material to [email protected] We are looking for experimental and theory applicants whose research agenda complements existing departmental strengths, including • nanoscale materials

Nanyang 13x2.indd 1 20/4/10 08:31:07

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M PW AD 0609 Odd Size BrightRecruits.indd 5 20/4/10 08:56:01 Join tomorrow’s MAX PLANCK INSTITUTE neutron stars for the science of light A light today ! for science ESRF Max-Planck Institute for the Science of Light Guenther-Scharowsky Str. 1/Bau 24 91058 Erlangen We are recruiting now. http://mpl.mpg.de Find job opportunities at: www.esss.se/jobs Principal Research Fellowship The Max-Planck Institute for the Science of Light (Russell Division) is seeking outstanding candidates for a Principal Research Fellowship (equivalent to a W2- engineers administrators level Associate Professorship). The successful applicant will have several years IT beam physics instrument scientists postdoctoral experience and an excellent track record in high-risk cutting-edge neutronics Join the ESRF photonics research. He/she will join a well-funded dynamic research group, target accelerator based in extensive new laboratories, with many opportunities for national and detectors Ph.D. Student Programme! international collaboration. As well as helping coordinate and advise a large and enthusiastic team of PhD students, postdoctoral researchers and visitors, the appointee will be encouraged to develop his/her own research projects. Work in a stimulating Thesis subjects cover Current research in the division focuses on scientific applications of photonic international environment frontline research in: crystal fibres, for example nonlinear optics and trapping in gas and vapour-filled with the prospect of physics hollow-core fibres (see www.pcfibre.com for more information). If desired, publishing in high-impact teaching opportunities may be arranged by agreement with the University of journals chemistry Erlangen-Nuremberg. biology The Max Planck Society is an equal opportunity employer. Applications from Gross salary 27 k€, women, disabled people and minority groups are particularly welcome. tax paid net salary >1550 €/month All new positions on Full applications or informal enquiries should be sent by email to personal@ 47-50 days of annual www.synchrotronjobs.com mpl.mpg.de (postal applications will not be accepted). The closing date is and compensatory leave June 28, 2010, although late applications may also be considered. Max-Planck or go to Institute for the Science of Light, Guenther-Scharowsky-Str. 1/Bau 24, D-91058 www.esrf.eu/jobs Erlangen, Tel: +49-9131-6877-301.

Lecturer (Two positions) Junior Scientist Experimental Condensed Matter Physics OPENING School of Physics on Faculty of Science 8VgZZgk^YZdhdc spatially resolved Raman spectroscopy ● Leading international university ● The Innovative Paul Scherrer and Institute creative is environmentwith 1300 employees the largest research centre for the ●natural Clayton and campus engineering sciences in Switzerland and a worldwide leading userA two-year position, as a junior scientist, is available at the Istituto Officina dei Materiali XZgcXdjg^Zg#Xdb laboratory. Its research activities are concentrated on the three main topics of solid-stateof the Italian Council of Research on EU FP7 funded project aimed at performing Raman The Opportunity physics, energy and environmental research as well as human health. spectroscopy with nanometric spatial resolution. The School of Physics seeks to appoint two Lecturers (Level B), who will lead the XZgcXdjg^Zg#XdbÉhWgVcY"cZlXVgZZgk^YZd developmentFor the use of atinnovative the beamlines research of programmes the Swiss Light in condensed Source (SLS) matter - one physics. of the most The successful candidate will have the opportunity to work Applicantsadvanced will radiation hold a PhD sources in an worldwide area relevant - the to Detector experimental Group condensed develops one-matter and two within the framework of an ambitious project funded by the EU hZXi^dch]dlXVhZhXVgZZgdeedgijc^i^ZhVi physicsdimensional and have high a record speed of solidpublications state detectors. and citations In ain collaborationthe highest impact between physics the ESRF commission which aims at the detection and identification of journals.(Grenoble, Successful France) applicants and PSI Eiger, will be a expectedlarge multi to module attract single national photon competitive counting pixel single unknown molecules in biological systems. The idea is `ZngZhZVgX]^chi^iji^dchVgdjcYi]ZldgaY# grants,detector establish system an for independent applications researchat synchrotrons, program, is being supervise developed. research students based on atomic force microscope manipulation and extraction and contribute to undergraduate teaching. The capacity for scientific outreach and of molecules out of their specific environment and on the experienceIn this respect, in engaging the SLS with Detector talented Group students is seeking would a be considered favourably. identification of the molecular composition through near-field For more information about the School of Physics, go to Raman scattering spectroscopy. The selected scientist will http://www.physics.monash.edu.au/ be in charge of the design and fabrication of new cantilevers All applicationsPostdoctoral should address theFellow selection criteria. Please refer to “How to Apply and of their implementation on a commercial AFM, in close for Monash jobs’ below. collaboration with the AFM manufacturer. She/He will also be Detector Development Swiss Light Source directly involved in the use of the set-up for tip enhanced Raman The University spectroscopy and microscopy. The scientist will benefit of a side Monash University has a bold vision - to deliver significant improvements to the by side collaboration with the neurobiologists in charge of the Your tasks human condition. Distinguished by its international perspective, Monash takes biological aspects and the physicist in charge of the optical v pride in Work its commitment on the development to innovative of the research pixel detectorand high (optimization quality teaching of the and system, (spectroscopic, photonic and plasmonic) issues of the project. performing measurements and data analysis) learning. Eligible candidates must hold a PhD and a solid post-doc v Implementation at beamlines experience in biophysics and nanotechnology. A former The Benefitsv Support of the detector systems and participation in X-ray experiments Remuneration package: $84,614 - $100,479 pa Level B (includes employer experience in scanning probe microscopy and/or design and superannuationYour profile of 17%).This role is a full-time position, however flexible working development of microscopic and spectroscopic equipment arrangementsYou hold a PhD may in bephysics negotiated. preferably Monash in the field offers of silicon a range detector of professionaldevelopment. Youand/or microfabrication is strongly recommended. The position is for one year, renewable for a developmenthave good programs, knowledge support of analog for research, and digital study electronics and overseas and sensors work, generous for solid statesecond year, starting from September 2010. Yearly gross salary is €33,000, according to national maternitydetectors. leave Experience and flexible in work C/C++ arrangements. programming, data analysis and experience inregulations. Further informations are available at the following websites: Durationsynchrotron Continuing radiation appointment instrumentation would be appreciated. http://www.cbm.fvg.it/laboratories/scanning_probe http://www.singlemoleculedetection.eu/ LocationYou will Clayton work as campus a team player in a stimulating international environment, giving youhttp://www.tasc.infm.it/~lazzarino/index.html excellent opportunities for new initiatives and independent research. Enquiries Only Interested applicants should submit a complete CV including list of publications and name of two Associate Professor Michael Morgan on +61 3 9905 3645 or email michael. referees (with e-mail address) by e-mail to: [email protected] For further information please contact: Dr Bernd Schmitt, phone +41 (0)56 310 23 14, Dr. Marco Lazzarino [email protected] No A1010606 IOM-CNR, Laboratorio TASC, Please submit your application to: Paul Scherrer Institut, Human Resources, Ref. code K^ZlLdg`^c\Vi?Z[[ZghdcAVWidYVnVi Applications Close Friday, 2 July 2010 Area Science Park, Basovizza, 34149 Trieste Italy XZgcXdjg^Zg#Xdb$Xlh$EV\Zh$_Z[[ZghdcaVWh#Yd 6114, Elke Baumann, 5232 Villigen PSI, Switzerland or to: [email protected] [email protected] Applicationswww.psi.ch via link below phone: +39.040.375.6434 http://monash.turborecruit.com.au/job/job_details.cfm?id=442421&from= fax: +39.040.226767 Physics World May 2010 65

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M CC AD 1109 Jefferson.indd 2 11/1/10 14:21:42 The Beilstein-Institut, located in Frankfurt am Main, is a leading, independent scientific foundation. An expanding programme of Open Access Journals is one of our major long-term projects. To add to our production team for our nanotechnology journal, we are currently seeking a full-time Scientific Editor (m/f) Responsibilities include: • Language editing and proofreading • Technical editing (editing and formatting of text and images) of scientific manuscripts • Production of html and PDF versions of articles • Support and monitoring of authors Qualifications required include: • Ph.D in physics, preferably nanotechnology, materials science or biophysics • Native English speaker; knowledge of German is desirable • Experience in scientific publishing an advantage We offer a competitive salary with pension contributions and a good working environment as part of a highly motivated team. The ideal candidate will have excellent English and copyediting skills, good IT and online ability, a fundamental knowledge in scientific writing and good knowledge of physics and nanotechnology. If you enjoy working as part of a team, have good communication skills and are able to work accurately and to deadlines, then please send your letter of application, together with a full Curriculum Vitae and an indication of your salary requirements and when you would be available, to: Beilstein-Institut zur Foerderung der Chemischen Wissenschaften Trakehner Str. 7-9 60487 Frankfurt am Main Germany E-Mail: [email protected] To apply for this position, candidates must be eligible to live and work in Germany. For further information see www.beilstein-institut.de. Advertise your vacancy to a global audience dci]Z_dWhlZWh^iZ[gdb>DEEjWa^h]^c\# www.brightrecruits.com

66 Physics World May 2010

M PW AD 0609 Odd Size BrightRecruits.indd 10 19/4/10 15:18:12 Home News Blog Multimedia In depth Jobs Events Buyer’s guide

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M PW AD 0410 Laser Interviews_07.indd 1 19/4/10 15:41:14 Lateral Thoughts: Captain Doctor Brunhilde Von Doom-Boots physicsworld.com A villain’s life in lasers

I remember when lasers first made the papers. The re- search journals in the main dismissed them as a minor extension of previous work, but we in the Informal Brotherhood of Supervillains recognized their potential almost straight away. After all, what is “light amplification by stimulated emission of radiation” but the careful or - ganization of a corralled population into an untenable iStockphoto.com/RapidEye situation, followed by a beam of high-energy, beefed-up photons goose-stepping towards your target? The very idea was too good to resist. So while scientists mocked lasers as “a solution looking for a problem”, we of the darker fraternity were working on problems for those do-gooders to solve. I recall one of the earliest attempts, when my dear friend Blofeld went for the classic common-or-garden “city ransom” approach. He was never terribly original, poor chap, and I was almost glad when he was foiled by that Etonian thug, Bond. It left the rest of us free to pursue far more creative applications. And there was the other chappie – Gold-something-or- I was an purposes. I mean, for Machiavelli’s sake, a significant pro- other. He got all inspired by his time as a sous-chef in the aspirational, portion of the population even save up to have their eyes Orient and decided that laser light would make the most irradiated with our old superweapon! And that’s not even sublime secret-agent sushi. It was not an unstylish idea, entry-level including the more frivolous medical uses. One simply even if in practice he had to downgrade his original laser nemesis cannot wreak havoc with a dermatology tool. You might scheme in favour of an oxy-acetylene torch and a flash- furtively as well menace people with an exfoliating pad. light. Technical difficulties, he said – but all in all it was pumping and For a while, I tried incorporating lasers into other super- really rather a good thing he ended up sparing Bond (him weapons. Lasers on rods launched into active volcanoes; again!), since the damned contraption would have made priming genetically engineered superwarriors who shoot laser rather a mess of his lair. semiconductors beams from their fingers; sharks with lasers à la my col- Of course, I was but a young stripling then. While the in my dad’s league Dr Evil; tidal-wave generators that would launch other kids were rocking round the clock, I was an aspir- shed pods of shark-mounted lasers at coastal cities…after a ational, entry-level nemesis furtively pumping and pri- while it just got ridiculous. I had to accept the difficult ming semiconductors in my dad’s shed. I still kept a truth that lasers had been left behind, and I with them. It transistor radio in my work area though, despite the drop was time to retrain. in productivity – have you ever tried to air-cool a ruby These days, I am doing an Open University course in crystal while distracted by thoughts of Keith Richards? genetics. Based on extensive readings of Nature, the He set me back weeks! Daily Mail and Michael Crichton, I gather that this is what But that moment – ah, that sweet moment when finely strikes terror into the hearts of the modern populace. So, unbalanced statistical energy distributions tumbled into every weekend (and some evenings if there is time after my a perfectly coherent beam, putting Busby Berkeley to Women’s Institute meeting), I go into my basement and shame. I remember it like it was yesterday. The sweet tamper with nature. I am hoping to create a race of hyper- ozone smell of success was surpassed only by the joy of coordinated wasps that will infiltrate key government demanding the return of my Rolling Stones album in the installations and hypnotize politicians with their synchro- best way possible: by firing a tight phalanx of photons into nized movements and subtle frequency combinations. As a the neighbours’ begonias. fallback, I am also working on a bacterium that will subtly So what if lasers were bulky? So what if they were ruin the texture of any jam it comes into contact with, as I heinously inefficient? They had character. They had soul. feel this would rapidly demoralize the nation – or at the very I loved them, and if it was up to me, we in the Brotherhood least win me the next WI preserve-making competition. would be menacing Lycra-clad men with them still. But It is hard work. Sometimes I feel the modern world is like many things, superweapons have moved on. I guess I moving too fast and I should settle down comfortably should not be surprised. Most of the soulful and personal instead of trying to follow it. But in my heart, I know I will technology from the last century is now regarded as some- never give up. Science is in my blood – or is that haemo- how hilarious just because it was a bit chunky – a sentiment globin? – and it never rests. And neither can you young that I am taking to heart increasingly as I age. whippersnappers reading this, whether you are a “human- But more to the point, maybe, perhaps the laser’s itarian” or one of our power-grabbing quango. You might demotion from its evil-weapon perch has come because it think your shiny new nanotechnology is the bee’s knees, is no longer cutting-edge, obscure, inaccessible technol- shark’s lasers or the sum total of every natural defence the ogy. CD players may retain a little yellow sticker saying platypus can muster – but remember, today’s grey-goo- “Danger – laser”, but no-one quivers at pieces of hi-fi mediated apocalypse is tomorrow’s run-of-the-mill nano- equipment pointed in their general direction. Worse still medicine. It can – and will – happen to you. are the health applications. Poor Goldie’s freeze-dried corpse would be turning in its orbit if he knew his in- Kate Oliver is a freelance science writer and author of the dustrial cutting lasers were being used for humanitarian Schrödinger’s Kitten blog, e-mail [email protected] 68 Physics World May 2010 The New HF2LI Lock-In Amplifier Your Application. Measured. Quantum and Nano-Physics, Microfluidics, Atomic Force Microscopy, Material Science, Semiconductors

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