High-Intensity Laser Targets

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www.laserfocusworld.com June 2012

International Resource for Technology and Applications in the Global Photonics Industry High-intensity laser targets

500 TW PAGE 15

Basics of Q-switching and modelocking PAGE 29 InGaAs FPA cameras improve NIR imaging PAGE 33 Yb fibers pump pulsed fiber lasers PAGE 43 Beam combining cranks up laser power PAGE 50

CIS solar cells made more effi cient PAGE 39

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International Resource for Technology and Applications in the Global Photonics Industry JUNE 2012 ■ VOL. 48, NO. 6

newsbreaks world news

9 15 Ultrahigh-Intensity Lasers OSU’s SCARLET laser Silver fi lm with cross-shaped nanoapertures aims for 500 TW/15 J/30 fs pulses is plasmonic quarter-wave plate 18 LED Optics Effi cient LED collimators have simple design

Luminescent solar cell that emits light 21 Cameras Time-of-fl ight camera sees around corners achieves record effi ciency 25 Quantum Optics Nanoresonator heralds promise Polystyrene graded-index POF has as new single-photon source 4.4 GHz bandwidth over 50 m

10 Mid-IR QC laser switches with near-IR telecom wavelength

12 Fused-silica cantilevers reveal femtosecond- pulse volume changes

columns departments

7 THE EDITOR’S DESK 68 IN MY VIEW 58 NEW PRODUCTS 66 BUSINESS Material comfort Who is going to run RESOURCE CENTER W. Conard Holton the Internet? 65 MANUFACTURERS’ Associate Publisher/Chief Editor Jeffrey Bairstow PRODUCT 67 ADVERTISING/WEB SHOWCASE INDEX

67 SALES OFFICES

LASERS ■ OPTICS ■ DETECTORS ■ IMAGING ■ FIBER OPTICS ■ INSTRUMENTATION

2 June 2012 www.laserfocusworld.com Laser Focus World

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15 COVER STORY 29 Solid-State Lasers 43 Specialty Fiber At the Science Center for Laser pulsing: The nuts and High-saturation-energy Advanced Research on bolts of Q-switching and Yb fi bers pump up pulsed Lasers and Engineered modelocking fi ber lasers Targets (SCARLET) laser facility in the High Energy Two versatile pulsing technologies— A 40 W, 2 mJ pulsed fi ber laser based Density Physics (HEDP) Q-switching and modelocking—are the on an ytterbium (Yb)-doped glass matrix group at Ohio State Uni- versity, the Petawatt De- basis of most commercial pulsed lasers with high saturation energy solves velopment Team’s pulsed in use today, for applications ranging many of the limitations associated laser targets a 500 TW peak power and 1021 W/ from medical imaging and diagnostics with traditional Yb-doped fi bers while cm2 intensity levels in a to attosecond science and industrial presenting several other advantages. 5 μm full-width-half-maximum spot size with a one- materials processing. Marco Arrigoni, Michel Bégin and Bertrand Morasse shot-per-minute repetition Magnus Bengtsson, and Matthias Schulze rate. The team plans to 50 Photonic Frontiers: install a deformable mirror in the laser chain to push 33 Low-Light Imaging Beam Combining SCARLET’s peak inten- 22 2 Scientifi c InGaAs FPA Beam combining sity beyond 10 W/cm . Courtesy of V. Ovchinnikov cameras heighten sensitivity cranks up the power ( ) for NIR imaging Coherent and wavelength beam With their high quantum effi ciency and combining have multiplied their output sensitivity in the important near- and power in the past few years, reaching Coming shortwave infrared range, deep-cooled, kilowatts both from coherently in July large-format InGaAs focal-plane-array combined fi ber lasers and from Field-portable cameras have many applications in wavelength beam combination lensless R&D. Ravi Guntupalli and Manjul Shah of diodes. Jeff Hecht microscopes aim for remote 39 Photonics Applied: 54 Organic Photovoltaics medical uses Microelectronics Processing Transition metal oxides Field-portable lensless Ultrafast lasers improve increase organic solar-cell microscopes based on effi ciency of CIS thin-fi lm power conversion holographic optics, LED solar cells Organic solar cells have struggled light sources, and image While nanosecond laser ablation and to achieve high power conversion sensors similar to those in mechanical scribing patterning processes effi ciency (PCE); however, transition cell phones have the for the integrated interconnects in copper- metal oxides can provide a major potential to revolutionize indium-diselenide (CIS) thin-fi lm solar cells PCE boost when used as electrode identifi cation of biological damage the fi lms through thermal effects modifi ers to improve open-circuit threats such as bacteria and mechanical forces, picosecond voltage, short-circuit current, and fi ll and parasites in remote laser processing offers a much more factor. Mark T. Greiner, Lily Chai, places. UCLA’s Aydogan successful alternative. Gerhard Heise, and Zheng-Hong Lu Ozcan describes the Helmut Vogt, Andreas Heiss, and Heinz P. Huber various approaches to the technology, designs for remote use, and potential applications.

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Two recent and successful trade shows have highlighted the breadth of applications that rely on photonics. SPIE Defense, Security + Sensing in April put the spotlight on military and security applications at its new venue in Baltimore. CLEO, held in San Jose in May, had a broader photonics reach with an em- phasis on research applications. Larger in market value than both of these application areas is materials processing, which is on display at LASYS in Stuttgart in June. This trade show again demonstrates the benefi ts of laser-based materials processing to industries as diverse as automotive manufacturing, construction, energy, and the life sciences. Several articles in this issue explore this topic, beginning with the use of ultrafast lasers to improve the effi ciency of CIS thin-fi lm solar cells. The article, written by Gerhard Heise and colleagues at the Laser Centre of the Munich University of Applied Sciences and solar module maker AVANCIS, describes how they have achieved a record effi ciency for CIS modules (page 39). An article by contributing editor Jeff Hecht covers beam-combining techniques developed at places such as MIT Lincoln Laboratory, Northrop Grumman, TeraDiode, and the University of Central Florida (page 50). And an article by Michel Bégin and Bertrand Morasse at CorActive shows how a fi ber laser based on an ytterbium-doped glass matrix offers advantages for pulsed-laser materials processing (page 43). Finally, Marco Arrigoni and colleagues at Coherent show the advantages of Q-switching and modelocking for pulsed lasers in applications ranging from medical imaging to industrial processing (page 29). For an even deeper understanding of lasers and materials, we will gain new insights into high-energy- W. Conard Holton density systems and ultra-intense light/matter interactions when the SCARLET laser in our cover story Associate Publisher/ goes on-line this month (page 15). The laser at Ohio State Univer- Editor in Chief sity will be aiming for 500 TW/15 J/30 fs pulses, making it one of [email protected] the most powerful lasers in the world.

Christine A. Shaw Senior Vice President & Group Publisher, EDITORIAL ADVISORY BOARD (603) 891-9178; [email protected] Stephen G. Anderson, SPIE; W. Conard Holton Editor in Chief, (603) 891-9161; [email protected] EDITORIAL OFFICES Dan Botez, University of Wisconsin- Madison; Connie Chang-Hasnain, Gail Overton Senior Editor, (603) 305-4756; [email protected] Laser Focus World UC Berkeley Center for Opto-electronic John Wallace Senior Editor, (603) 891-9228; [email protected] PennWell Corporation Nanostructured Semiconductor Carrie Meadows Managing Editor, (603) 891-9382; [email protected] 98 Spit Brook Road, LL-1, Nashua, NH 03062-5737 Technologies; Pat Edsell, Avanex; Lee Mather Associate Editor, (603) 891-9116; [email protected] (603) 891-0123; fax (603) 891-0574 Jason Eichenholz, Ocean Optics; Thomas Giallorenzi, Naval www.laserfocusworld.com Susan Edwards Executive Assistant, (603) 891-9224; [email protected] Research Laboratory; Ron Gibbs, Ron Gibbs Associates; CONTRIBUTING EDITORS CORPORATE OFFICERS Anthony M. Johnson, Center for Advanced Studies in Photonics Jeffrey Bairstow In My View, [email protected] Frank T. Lauinger Chairman Research, University of David A. Belforte Industrial Lasers, (508) 347-9324; [email protected] Robert F. Biolchini President and CEO Maryland Baltimore County; Jeff Hecht Photonic Frontiers, (617) 965-3834; [email protected] Mark Wilmoth Chief Financial Offi cer Kenneth Kaufmann, Hamamatsu D. Jason Palmer Europe, 44 (0)7960 363 308; [email protected] Corp.; Larry Marshall, Southern TECHNOLOGY GROUP Cross Venture Partners; Jan Melles, Photonics Investments; Adrienne Adler Marketing Manager Christine A. Shaw Senior Vice President/ Masahiro Joe Nagasawa, TEM Co. Suzanne Heiser Art Director Group Publishing Director Ltd.; David Richardson, University of Southampton; Ralph A. Rotolante, Sheila Ward Production Manager Subscription inquiries Vicon Infrared; Samuel Sadoulet, Chris Hipp Senior Illustrator (847) 559-7520; fax (847) 291-4816 Edmund Optics; Toby Strite, Debbie Bouley Audience Development Manager e-mail: [email protected] JDS Uniphase. Alison Boyer Ad Services Manager web: www.lfw-subscribe.com

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newsbreaks

Silver fi lm with cross-shaped nanoapertures is plasmonic quarter-wave plate w Researchers at the University of Mel- ness of 140 nm, an array period ℓ bourne (Victoria, Australia) and Casix (Fu- d in both dimensions of 400 nm, y w d zhou, China) are computationally modeling and crosses with a constant line- y ℓ plasmonic optical wave plates that consist width w of 40 nm, but with dif- x of a periodic array of cross-shaped nano- fering line lengths l and l . The x y x apertures in a silver fi lm. For example, they period is large enough to keep have designed a quarter-wave plate for op- localized aperture resonances well sepa- of the cross. The analysis showed that pat-

eration at a specifi ed wavelength in the in- rated from resonances arising from surface- terns with lx of 193 nm and 229 nm would frared. The wave-plate quality is created by plasmon excitation. In one instance, ly is behave as partially transmitting quarter- making the cross shapes asymmetric. held fi xed at 210 nm and lx is varied from wave plates at 710 nm (left circularly polar- The 2D structure—which was modeled 170 to 250 nm. The resulting transmission ized) and 760 nm (right circularly polarized), using multiphysics software by COMSOL spectrum has two peaks that arise from respectively. Contact Ann Roberts at ann. (Burlington, MA)—has a silver fi lm thick- the excitation of the resonance in each arm [email protected].

Luminescent solar cell that emits Polystyrene graded-index light achieves record effi ciency POF has 4.4 GHz While the concept seems fundamentally counterintuitive, researchers at the Univer- bandwidth over 50 m sity of California–Berkeley (UC Berkeley) have suggested and demonstrated that a Home networks based on graded-index highly effi cient solar photovoltaic (PV) cell is also an effi cient emitter of photons. A plastic optical fi ber (GI-POFs) can have luminescent solar cell prototype developed by Alta Devices (Santa Clara, CA), the high data transmission rates in the giga- company that is commercializing the technology, achieved a 28.8% optical-to-elec- bits/second range. Conventional fi bers for trical conversion effi ciency—record performance for a single-junction PV cell and these networks are based on poly(methyl fast approaching the 33.5% theoretical Shockley-Queisser effi ciency limit. 1.600 Based on the thermodynamic link between absorption and emission, a solar cell 1.598 that easily emits photons also produces a higher voltage. When absorbed sunlight Approximated in the gallium-arsenide structure produces electrons and holes, these carriers have 1.596 no place to go at the open-circuit condition. The carrier-density buildup causes ex- 1.594 ternal fl uorescence that balances the incoming sunlight. An external fl uorescence Measured improvement from high carrier density also occurs in the best light-emitting diode 1.592 (LED) devices. High carrier density 1.590 produces high voltage and like- 0.0 0.2 0.4 0.6 0.8 1.0 Normalized fiber radius (a.u.) wise, improved optical-to-electronic conversion effi ciency. That methacrylate) (PMMA), which has a trans- is, the best solar cells behave just mission peak at 650 nm and a much lower like ideal LEDs, with very low non- transmission at 670–680 nm. Howev- radiative losses and internal lumi- er, vertical-cavity surface-emitting lasers nescence effi ciency values much (VCSELs) emitting at 650 nm are lower in greater than 90%. Contact Owen power and less thermally stable than those Miller at [email protected]. emitting in the 670–680 nm range. Now, researchers at Polystyrene continued on page 10

Laser Focus World www.laserfocusworld.com June 2012 9

newsbreaks

Mid-IR QC laser switches with near-IR telecom wavelength Researchers at Northwestern University’s optical communica- a) Ge b) SEM Bio-Inspired Sensors and Optoelectron- tions, and laser range- 6.1 μm resonant absorber ics Laboratory (BISOL) led by Profes- fi nding. antenna sor Hooman Mohseni have used a novel The optical nanocir- QCL gap-loaded nanoantenna that shows cuit is extremely small ridge laser

resonance at dual wavelengths when in- (less than half a cubic 1.55 μm tegrated onto the facet of a quantum- micron) and integrat- resonant antenna 1 μm cascade laser (QCL). The antenna design ed directly at the laser c)E-intensity d) E-intensity 2 2 2 2 shows resonance at the QCL wavelength facet. When light at y (μm) (V/m) /(mW/μm ) y (μm) (V/m) /(mW/μm ) (×10-7) (×10-7) of 6.1 μm and the switch-beam wave- 1550 nm is coupled 1.5 Reflected signal – 1.5 Reflected signal – 1550 off 14 1550 on 14 length of 1.55 μm. Coupled by a nonlin- to the antenna, its in- 1.0 12 1.0 12 0.5 10 0.5 10 ear nanoswitch, the two antennas differ tensity is enhanced 0.0 8 0.0 8 from other gap-loaded nanoantennas in by the smaller bow- -0.5 6 -0.5 6 -1.0 4 -1.0 4 that the cross-polarized switch beam an- tie. This changes the -1.5 2 -1.5 2 0 0 tennaallows forenhanced absorption refractive index of -2 -1 0 1 2 -2 -1 0 1 2 x (μm) x (μm) in the gap-loaded germanium region, the germanium, and which increases the switching efficien- therefore modulates the larger antenna approximately 15% at the switch-beam cy. With switching power on the order and thus the overall QCL power. Experi- power of 70 μW, resulting in a switching of picojoules, the dual-wavelength op- mental data for the device shows ex- energy of 8.4 pJ—comparable to other eration of the device suggests applica- cellent agreement with simulation data. all-optical switch designs, but with a tions in telecommunications, free-space The device shows a modulation depth of much smaller device size. Contact John Kohoutek at johnkohoutek2008@u. northwestern.edu. Optical Isolators from Polystyrene continued from page 9 Keio Universi- ty (Kawasaki and Yokohama, Japan) have developed a GI-POF based on polystyrene, which has higher transmission at the longer wavelengths, allowing use of the more-optimum VCSELs. The preform was fabricated via the rod-in-tube method and drawn down to core and cladding diameters of 400 and 700 μm, respectively. The measured refractive-index profile (red line) closely fits an approximation fit to a power law with an exponent of 3.3. One requirement for a home GI-POF system is that the fiber attenuation be less than 200 dB/km. The polystyrene fiber has a low loss of 166– Specializing in High Power Applications 193 dB/km at 670–680 nm wavelengths, much lower than the approximately 270 EOT Isolators provide excellent beam quality while protecting lasers dB/km for a PMMA fiber. Tests showed from back reflections. Whether you have a SSL, Fiber Laser, Laser a bandwidth for a 50 m stretch of poly- Diode or QCL, EOT has an isolator solution for your application. styrene fiber at 670–680 nm to be 4.4 GHz. In addition, the fiber material is a Electro-Optics Technology, Inc. commodity resin and thus very inexpen- www.eotech.com●[email protected]●231______-935-4044 sive. Contact Yasuhiro Koike at koike@ appi.keio.ac.jp.

10 June 2012 www.laserfocusworld.com Laser Focus World

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newsbreaks

Fused-silica cantilevers reveal femtosecond-pulse volume changes At certain fl uences below the ablation scanning the laser beam in a pattern, fo- threshold, ultrafast-laser pulses pro- cusing just below the surface. The result duce changes in fused silica including is that any volume changes produced by the formation of self-organized patterns the laser action cause a beam to defl ect consisting of “nanogratings.” Suspect- through an angle, providing a quanti- Introducing ing localized densifi cation coupled to tative measure of local volume change. PulseLineTM ultra-fast stress accumulation and relaxation in the Light from a laser emitting 380 fs puls- nanograting regions, Audrey Champoin es at 1030 nm and an 860 kHz repeti- laser mirrors from and Yves Bellouard of the Eindhoven Uni- tion rate was focused through an objec- Semrock versity of Technology (Eindhoven, the tive with a 0.40 numerical aperture and Netherlands) have developed an experi- scanned across the cantilever surfaces, mental technique to test volume changes with the light polarization either trans- in fused silica produced by exposure to verse or parallel to the scanning direction. femtosecond-laser pulses. The defl ections (50 to 90 μm) showed a High reﬂectivity (R > 99.3%) In the technique, a number of fused- volume expansion with exposure and a Broadband performance silica cantilevers are oriented parallel to possible weak dependence on polariza- for Ti:S lasers each other side by side and fi xed at one tion; relative estimated expansion was end to an anchor point. One cantilever is 0.03%. Principal stresses were on the or- Low dispersion not illuminated and serves as the control; der of 300 MPa. Contact Yves Bellouard High Laser Damage the others are illuminated on one side by at [email protected]. Threshold Very low absorption Low scatter Pulsed CO2 Lasers

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camera views around corners world news See page 21

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ULTRAHIGH-INTENSITY LASERS OSU’s SCARLET laser aims for 500 TW/15 J/30 fs pulses

“When the SCARLET laser comes online in June 13, 2012 rate. Typically, large-scale laser systems are only able to hit [with experiments beginning in August], it will be one of the several shots per day at most,” says Chowdhury. most powerful lasers in the world and the highest-peak-pow- “One of the primary goals of SCARLET is to reliably run ex- er sub-one-hundred-femtosecond laser in the United States,” periments consisting of hundreds of shots per day, allowing says Enam Chowdhury, senior research associate and leader our HEDP group to more accurately model high-energy-den- of the Petawatt Development team in the Science Center sity systems and to truly understand just what happens in ul- for Advanced Research on Lasers and Engineered Targets tra-intense light/matter interactions,” adds professor Richard (SCARLET) laser facility in the High Energy Density Phys- Freeman, the HEDP Laboratory group leader. ics (HEDP) group at Ohio State University (Columbus, OH). Chowdhury says that the 815 nm center-wavelength SCAR- SCARLET laser parameters LET laser was engineered to reach a 500 TW peak power Although its maximum peak power aims at 500 TW, SCAR- and 1021 W/cm2 intensity levels with 30 fs pulsewidth, 15 J LET will be known as a 0.5 PW or petawatt-class laser that pulses in a 5 μm full-width-half-maximum spot size with a will operate in two modes, including a short-pulse kilohertz one-shot-per-minute repetition rate. In 2013, installation of mode (0.1–0.8 mJ, 25 fs pulses at 1 kHz) with a wavelength a deformable mirror will be completed in the laser chain to range of 0.8–4.0 μm for laser damage studies. push SCARLET’s peak intensity beyond 1022 W/cm2. Maximum power is achieved in SCARLET by sending the While the specifi cations are impressive, the repetition rate kilohertz-level laser output through an additional mirror- is particularly noteworthy. “The usability of current ultra-in- stripe grating stretcher (pulses stretched to 800 ps) in a tense laser systems is limited, owing to their low repetition dual-chirped-pulse-amplifi cation (DCPA) architecture followed by various pulse-cleaning ap- paratuses, including a cross-polarized wave (XPW) generator system. The pulse also travels through a number of Ti:sapphire multipass amplifi ers with the fi nal amplifi er being pumped with two 25 J/pulse neodymium pump lasers at 527 nm and a new compressor that uses a pair of 36-cm and 56-cm- long diffraction gratings. The entire laser system is housed in a Class 1000 cleanroom complete with entrance air shower and networked temperature and humidity sensors. The SCARLET laser output is then directed under vacuum into a 1200 ft2 target room and compressed inside a The SCARLET laser at Ohio State University will be used to study light/matter interactions with 10.5-ft-long, 6-ft-diameter cylindrical its 500 TW, 30 fs output. (Courtesy of V. Ovchinnikov, HEDP) vacuum chamber before being sent to

Laser Focus World www.laserfocusworld.com June 2012 15

the fi nal f/2 focusing off-axis parabo- eter, Thompson parabola, interferom- Planned experiments la inside a 35-port chamber with a 3-ft, eter, HOPG x-ray spectrometer, x-ray The interaction of ultrahigh-intensity, 7-in. diameter and a 3-ft, 6-in. height. pinhole imaging camera, and K-alpha ultrashort-pulsed laser light with solid In addition to its eight laser diagnos- bent-crystal imaging spectrometer di- targets is the primary area of study for tic devices, including on-shot focal spot agnostic instrumentation, all assisted SCARLET researchers. “While the sun and spatial chirp diagnostics, SCAR- by a six-node computer cluster with 48 illuminates our world with an approxi- LET also includes x-ray diode, pre-plas- cores and 130 Gbytes of RAM per node mate 0.1 W/cm2 at the surface of the ma shadowgraphy, Schlieren imaging, and a 10 Tbyte RAID (redundant array earth, SCARLET’s 22 to 23 order-of- gamma-ray and neutron spectrom- of independent disks) storage array. magnitude intensity increase allows study of light/matter interactions under star-like conditions in a laboratory setting,” says Kramer Akli, senior research scientist who heads the experimental WE MAKE IT campaigns at SCARLET. One anticipated area of study is fast- Stock and Custom Filters ignition fusion. Unlike the National Ig- nition Facility (NIF) program that requires 192 laser beams with 5 kJ each Optimize Throughput and Improve Signal Detection with Filter Coatings Designed for your Application When the SCARLET laser comes online, it will be one of the most powerful

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MIL-STD-810F: 10 Day factured with relatively modest pre- Humidity Durability MIL-C-48497A, Section cision for a less-expensive, easier-to- 3.4.1 maintain fusion energy source. The SCARLET laser can assist with understanding how laser pulses can best ig- nite laser fusion targets by analyzing particle and energy transport through hot dense matter. And in addition to experiments in more optics | more technology | more service laser-driven x-ray technology and its use as a potential neutron/gamma-ray HOW CAN WE HELP YOU? source, SCARLET will also be used to Contact our Sales Department USA: +1-856-547-3488 ASIA: +65 6273 6644 today for a quote! EUROPE: +44 (0) 1904 788600 JAPAN: +81-3-5800-4751 generate energetic protons for studies in proton fast ignition, proton radiography for material diagnostics, and for proton www.edmundoptics.com/coatings therapy—a form of radiation therapy to combat cancer. —Gail Overton

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LED OPTICS Effi cient LED collimators have simple design Two nonimaging LED collimating lenses limates light from the LED at large cone ladder surface, through which rays re- developed by engineers at the Chinese angles. The third surface is a spherical fl ected from the parabolic surface exit Academy of Sciences and Xi’an Jiaotong section near the LED designed to pass without a change in direction; the lad- University (both in Xi’an, China) were rays into the lens at normal incidence der-like shape is to minimize the volume designed using a simple and quick pro- to the surface. The fourth is a so-called and weight of the lens. cess, unlike the complex iterative software design usually used for LED optics.1 b Parabola b The collimators are very effi cient and fo- Surface 1 cus at least 80% of an LED’s light within Lens a 5 m radius that is 200 m away from Lens the light source. Air a Air a Lens Surface 1 Surface 2 Air Refractor on the outside Air The fi rst type of lens consists of four LED LED types of surfaces. The fi rst surface has These two types of rotationally symmetric LED an aspheric profi le and is designed to collimating lenses can be straightforwardly collimate light emitted from the LED at designed without the use of iterative smaller cone angles. The second surface algorithms. In both cases, the LED defi nes is a parabola with the LED at the focus the optical axis. An example of the second (see fi gure); this surface collects and col- type of lens is shown at right. New Bench-Top Fluorometer

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The design of the surfaces is straight- radius of the spherical section is “a” and In this case, modeling showed that a lens forward, with only a couple of things the axial distance from the LED to the with the cylinder radius a = 8 mm and the to keep in mind. First, surface 1 must edge of the center asphere is “b.” axial distance to the aspheric refractor edge end at or before the diameter at which For a lens of type 1, models were cre- b = 20 mm showed a spot at 200 m, with a ray from the LED strikes the surface at ated with a = 8 mm and b = 8 mm; a = about 90% of the light rays falling within the critical angle (beyond which the ray 14 mm and b = 14 mm; a = 8 mm and a 5 m radius ( similar results held for most would be totally internally refl ected). Sec- b = 20 mm; a = 14 mm and b = 20 mm; other modeled lens dimensions as well). and a = 20 mm and b = 20 mm. As ex- The two lens types showed effi cien- The researchers note that pected, the larger lenses produced small- cies (the percentage of light from the many LEDs today have er collimated spots, with the lens with source successfully passing through the b = 20 mm and a = 20 mm producing a lens) of about 90% and 99%, respec- chip sizes smaller than beam with 94.9% of rays falling within a tively. While the second lens type has a 1 × 1 mm. 3.5 m light-spot radius at 200 m, and the lower effi ciency, it is also much shallow- lens with a = 8 mm and b = 20 mm pro- er than the fi rst type for the same a and ond, the ladder shape must not get in the ducing a beam with 98.5% of rays falling b: For a = 8 mm and b = 20 mm, the way of the ray from the LED that refl ects within a 4 m light-spot radius at 200 m. fi rst type has a depth of 103 mm, while from the outer edge of the parabola. the second is only 38 mm deep. In a simulation, a 1 × 1 mm LED chip Refractor on the inside The researchers note that many LEDs emits at a wavelength of 500 nm. One The second type of collimating lens also has today have chip sizes smaller than 1 × 1 hundred thousand rays are traced to an four surface types. The fi rst surface is a lad- mm; using these LEDs will produce even illuminated plane 200 m away. The lens der-type fl at surface; the second is an axial better results. —John Wallace is made of molded polymethyl methacry- aspheric refractor; the third is an aspheric REFERENCE late (PMMA) and is assumed to be non- refl ector; and the fourth is a cylindrical sur- 1. G. Wang et al., Appl. Opt., 51, 11, 1654 (April absorptive and free of scatter. Here, the face passing rays to the refl ector. 10, 2012).

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CAMERAS Time-of-fl ight camera sees around corners

First conceptualized by Massachusetts In- Beamsplitters a) stitute of Technology (MIT; Cambridge, Ultrafast laser MA) researchers and reported on by La-

ser Focus World back in late 2010, an ul- r1 L trafast camera that could potentially see Photodetector Galvo around corners has now been experimen- tallydemonstratedby membersof the Streak camera r4 W original research team at the MIT Media r2 Occluder r Lab.1 By using time-of-flight techniques 3 Wall and computational algorithms to decode Intensity (a.u.) diffuse reflections from a 3D object con- b) c) cealed around a corner, the streak-cam- s era-based setup—similar to that used 1 by the MIT Media Lab to create trillion- Object T (ns) (hidden) frame-per-second visualizations—is able to reconstruct the shape of the object. 0 0 672 X (pixels) The diffuser wall Confidence (a.u.) An important part of the experimental Diffuse reflections from an object placed behind an opaque divider are captured by a streak- setup for around-the-corner object re- camera-based system (a). The streak images (b) and computational algorithms are used to construction is a 40-cm-high, 25-cm- reconstruct a 3D image of the hidden object (c). (Courtesy of MIT Media Lab)

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Reconstruction all laser positions and all pixels on the By scanning the laser and recording suc- wall observed by the camera. cessive streak images, triangulation and Each pixel in the streak image corre- reconstruction algorithms are used to de- sponds to a fi nite area on the diffuser code the diffuse refl ections into a 3D set wall and a 2 ps time interval, creating a of data that can be used to reconstruct discrete space-time bin. But the effective Made Possible SPECTOR®-HT Ion Beam Deposition System with Fluid Jet Polishing

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time resolution of the system is 15 ps Flow... due to the fi nite temporal point-spread function of the camera. In a process Fluoresce... called backprojection, the streak images and time-of-fl ight data are used to cal- iFLEX culate the probable physical locations of points from the object in the image Your innovation inspires us to plane, allowing creation of a 3D depth create photonic technologies that map for the concealed object. empower and differentiate. Data from the 3D range setup are used to compute a fi nal image and submillime- Qioptiq’s Flexible Laser Technology ter-precision depth map with centimeter- provides the ultimate versatility in scale lateral precision for a concealed ob- laser delivery for DNA sequencing, ject in a 40 × 40 × 40 cm3 volume. “The ophthalmology, ﬂow cytometry, ability to look around the corner with its microscopy, metrology and wafer many applications is only one example of processing. Get Flexible... Discover what is possible in this new research area Qioptiq today. between computational imaging and ultrafast optics,” says Andreas Velten, a member of the research team at MIT. “We hope to inspire more research proj- ects in this fi eld.” “Going from an x-ray machine to a CAT-scan machine required a clever co-design of hardware and computa- tion via tomographic reconstruction; similarly, going from a traditional hardware such as time-of-fl ight radar to approaches like CORNAR [see ____http://

cameraculture.info]______to look around corners requires a new generation of mathematical tools,” says Ramesh Ras- kar, MIT Media Lab associate professor. “Our Nature Communications paper with collaborators and my own earlier white papers indicate some of the future directions of such a joint hardware-software approach. Initially, the technique will be targeted at controlled settings for scientifi c, medical, and industrial imaging. But over time, as ultrafast imaging improves, more portable and lower-power form factors should enable a range of indoor and outdoor solutions from robotics, vehi-

______cles, factory automation, fi rst respond- ers, and computational photography.” —Gail Overton

REFERENCE 1. A. Velten et al., Nat. Comm., 3, 745, 1–8 (Mar. ______20, 2012).

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QUANTUM OPTICS Isolate... Nanoresonator heralds promise Intensify... as new single-photon source

A team of German researchers has de- other wavelength has been generated. Q-SWITCH veloped a versatile and effi cient source Much recent work has made use of Your innovation inspires us to of photon pairs that shows promise as a this trick, and recently researchers at create photonic technologies that means of generating defi nitively single Humboldt University (Berlin, Germany) empower and differentiate. photons for quantum information and established the statistics of the process cryptography applications. when they carried it out in a periodically Make Qioptiq your source for high- The properties of single photons are poled potassium titanium oxide phos- performance electro- and magneto- 1 themselves of great interest in fundamen- phate (KTP) crystal. But for maximum optics. Our extensive line of Pockels tal studies, and the promise of absolute utility, the ideal single-photon gun should Cells, Faraday Isolators and Laser security in quantum Modulators ensure you of exacting cryptography using beam modiﬁcation and control. photons can only be Specify precision... Discover Qioptiq. fulfi lled with a source of photons that are emit- RTP, ADP, LiNbO3, BBO, TGG, ted singly every time. KD*P and Others Much work has UV / VIS / IR, 250nm – 3μm therefore gone into developing a reliable In a schematic of the photon pair production process, a Apertures from 2.6 – 12mm diamond prism separates pump light from “herald” idler and single-photon source, signal photons. (Courtesy of M. Foertsch et al.) Patented Design for Minimal rather than those that Piezoelectric Oscillation can emit in bunches or pairs. Research- have narrow but tunable bandwidth, Exceptional Transmission ers are getting closer to an ideal single- so that atomic transitions can be “ad- photon gun: one that emits single pho- dressed” in quantum information and Maximum Extinction Ratios and Damage Thresholds tons with impeccable reliability and good storage applications, for example. The effi ciency, narrow bandwidth, and wide photons’ wavelength should also be tun- Custom Solutions Delivered tunability. able, so that a number of different atoms might be used. Spontaneous parametric Now, researchers from the Max Planck down-conversion Institute for the Science of Light (Erlan- One promising way to do that has come gen, Germany), the University of Erlan- to the fore in recent years is spontane- gen-Nuremburg, and the University of ous parametric down-conversion (SPDC). Paderborn (Paderborn, Germany) have Part of the family of nonlinear wave-mix- come up with a design for a photon gun ing processes, SPDC occurs in some crys- that fulfi lls these requirements.2 tals, turning a small fraction of input photons into pairs whose energies sum to the Whispering-gallery-mode input photon energy. resonator In general, the photons are of differ- Their starting point is a whispering-gal- ent wavelengths, so it is straightforward lery-mode resonator: a disk-shaped cav- to fi lter the output into the three differ- ity made of lithium niobate, a mate- ent types—the pump, and the resulting rial whose SPDC properties are well signal and idler. The process is suited for known. It is pumped with a few hundred applications in which single photons are nanowatts of light from a frequency- required because one of the pair acts as doubled Nd:YAG laser at 532 nm coupled a “herald”: Catch one wavelength with a in through a diamond prism. Residual detector and that detection is a guaran- 532 nm light, as well as the signal and tee that one and only one photon of the idler wavelengths of around 1030 and US/CAN: 800-429-0257 UK: +44 2380 744 500 EUR: +49 551 69 35-0 ASIA: +65 64 99 77 66 Laser Focus World www.laserfocusworld.com www.qioptiq.com [email protected]

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1100 nm, are coupled out using the same the quantum information community has prism, which separates them spatially. come up with in recent years. Magnify... The results showed a good degree “This compact source provides unprec- of “antibunching” of the output pho- edented possibilities to couple to differ- Resolve... tons—proving the single-photon nature ent physical quantum systems and ren- of the split signal and idler streams, with ders it ideal for the implementation of AUTOMATE an output of 13 million photon pairs per quantum repeaters and optical quantum milliwatt of pump power. But the real information processing,” the researchers Your innovation inspires us to strength of the design is its fl exibility. The wrote in their preprint. create photonic technologies that monolithically produced resonator itself “Our results mark the starting point of empower and differentiate. can be heated, resulting in a tunability a new class of resonator-enhanced SPDC Qioptiq couples integration expertise of the output photons by a range of 100 sources, simultaneously easily tunable with a wide range of Optem micro- nm (about 50 nm in each beam). in bandwidth and wavelength while inspection lens systems to deliver The lowest bandwidth the team mea- offering a compact, stable, and easy to automated microscopy solutions for sured was 7.2 MHz, which was tuned up implement design with remarkable to 13 MHz simply by changing the dis- effi ciency.”—Jason Palmer wafer processing, vision metrology, tance of the coupling prism for the resona- and micro/nano manufacturing. Take REFERENCES a closer look... Discover Qioptiq. tor. Taken together, the results suggest that 1. M. Scholz et al., Phys. Rev. Lett., 102, 063603 (2009). the design is perfectly suited to the many 2. M. Foertsch et al., arXiv preprint 1204.3056 QW different technologies and approaches that (submitted to Nature). X Q Laser Focus World Y editors get ‘real’ QZ Our latest addition to the breadth of industry experts, entrepreneurs, Y[ technical resources on www.laser and academics on hot topics and focusworld.com is the Laser Focus emerging markets. If you have a \ World Video Journal. Consider it our topic or development you’d like to version of reality TV for photonics discuss on the Video Journal, please and optoelectronics junkies! Editors get in touch through our Contact Conard Holton, Gail Overton, John page at http://bit.ly/NeZLK3. We’d Wallace, and Lee Mather talk to love to hear from you!

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SOLID-STATE LASERS

Laser pulsing: The nuts and bolts of Q-switching and modelocking

MARCO ARRIGONI, MAGNUS BENGTSSON, and MATTHIAS SCHULZE

Two versatile pulsing technologies— mulated in the laser lators. In an EO modulator, a crys- Q-switching and modelocking—are the crystal (assumed to tal rotates the polarization of light have a long upper- passing through it when a voltage basis of most commercial pulsed lasers state lifetime). The is applied. By inserting this crystal in use today, for applications ranging Q-switch state is then between two crossed polarizers, light from medical imaging and diagnostics changed, and the cav- can only pass through this assembly to attosecond science and industrial ity loss quickly drops when the applied voltage rotates the materials processing. to zero. This causes a polarization. EO modulators are short pulse to build typically used at low pulse-repeti- While there is a very broad selection of up by using all the stored gain. The tion rates (up to a few kilohertz) and pulsed lasers currently available, the combination of stored gain and short high pulse energies, commonly in the vast majority rely on just two puls- pulse rise and fall times results in a range of multiple millijoules per pulse. ing techniques—namely, Q-switch- high peak power pulse with durations For higher pulse-repetition rates ing and modelocking, able to deliver of a few nanoseconds up to a few hun- (tens of kilohertz or more) and lower nanosecond or picosecond/femtosec- dred nanoseconds. pulse energies, an AO modulator is ond pulses, respectively. This article The most commonly used usually preferred. In an AO modu- reviews the basics of each technology, Q-switch devices are electro-optic lator, the crystal defl ects the intra- the output characteristics that they de- (EO) and acousto-optic (AO) modu- cavity beam by a fi xed angle when liver, and a few of the many applications that they support. Pumpmp lightligh in Pumpmp lightligh in Q-switch Q-switch Q closed open -switching High High Laser A Q-switch is essentially a shut- reflector reflector output Laser crystal Output Laser crystal Output ter with a very fast response time coupler coupler placed inside a laser resonator. In one state (low Q) it creates cavity loss, preventing lasing; in Cavity the other (high Q), it has essen- loss FIGURE 1. Cavity loss, stored tially no loss, so lasing can occur. energy, and output power are Key steps of the Q-switching plotted as a function of time process include the Q-switch in a Q-switched laser cavity Stored (bottom); the dashed vertical state (cavity loss), energy storage, energy lines denote one cycle of the and output power as a function process, which results in a of time (see Fig. 1). At the start single laser pulse. This cycle of each cycle, the Q-switching Output typically lasts anywhere from element is set to prevent las- power about 10 μs to 1 ms. The ing. While the Q-switch is in production of a Q-switched this mode, the pump energy, 1 Time pulse is depicted at top. supplied continuously, is accu- Repetition rate

Laser Focus World www.laserfocusworld.com June 2012 29

SOLID-STATE LASERS continued

radio-frequency (RF) power is applied, dom phase relationships relative to each ity round trip rate, which is on the order thus preventing lasing. other. In modelocking, the relative phase of 76 MHz for a typical commercial of all these modes is fi xed. Fourier anal- Ti:sapphire oscillator. Modelocking ysis shows that the resultant superposi- Passive modelocking can be per- Modelocking is a special operating con- tion of modes manifests itself as a very formed through the so-called Kerr lens dition of continuous-wave (CW) laser short pulse that travels around the cav- effect in the gain material. Here the high materials that is used for generating ity at the speed of light. Every time this peak intensity associated with mode- output with femtosecond or picosec- pulse reaches the output mirror, the laser locked operation induces a refractive- ond pulse duration. Laser materials emits a part of this pulse. index change (equivalent to a lens) in the with a wide gain bandwidth, such as The shortest possible laser pulsewidth laser crystal. This lens focuses the beam, Ti:sapphire, can produce a broadband (called the transform-limited pulse- enabling it to pass through an internal output (tens of nanometers of more). width) ultimately depends on the num- aperture suffering only minor losses. In Detailed examination reveals that this ber of modes involved. Since the pulse contrast, CW operation would result in output consists of hundreds, thousands, duration is the Fourier transform of the clipping and attenuation. Another passive or even tens of thousands of individual spectral bandwidth of the laser, broader modelocking technique uses a “bleach- longitudinal modes, each satisfying the bandwidths support shorter pulsewidths able” optic, such as a saturable Bragg equation: and vice versa. The pulse repetition rate is refl ector (SBR). This is a special cavity determined by the round trip time of the mirror that only approaches 100% refl ec- Nλ = 2 × cavity length (where N is a laser cavity. For example, in a Ti:sapphire tivity when its absorbing semiconduc- large integer) laser oscillator with a cavity length of less tor layer is overloaded by the high peak than 2 m and a bandwidth greater than power of modelocked operation. In most lasers, these modes randomly 100 nm, the repetition rate is 76 MHz gain and lose intensity, and have ran- and the pulsewidth can be close to 10 fs. Q-switched pulses A CW laser can be forced into mod- for materials processing elocked operation by any mechanism Effi cient pulsing of a laser beam yields NEW PRODUCT! that provides lower optical losses when short pulses with high energy and high the laser runs in this regime rather than peak power. Q-switching is most com- MID-IR FOCUSING in a CW free-running regime. There monly used with neodymium (Nd) doped

OBJECTIVES are two categories of modelocking that laser hosts such as Nd:YAG, Nd:YVO4, 2μm -12μm can be used, called active and passive and Nd:YLF. The dominant application mode locking. Active modelocking refers for these diode-pumped, Q-switched la- to fast gating of the cavity (for exam- sers is in materials processing, and partic- ple, using a AO modulator) at the cav- ularly precision micromachining, across most sectors of semiconductors/electronics and related industries (see Fig. 2). Q-switched di- 27.5 μm ode-pumped solid-state (DPSS) lasers, such as • Diffraction limited focal spot the Coherent AVIA and • ZnSe micro-aspheric Matrix series, provide ␭ • AR-AR at Mid-IR ’s ideal fl exibility for these • Easy alignment using HeNe applications in terms of • Standard RMS or 1''plate diversity of power, pulse 50 μm In stock for immediate delivery repetition rate, and wavelength. FIGURE 2. In the manufacture of thin-fi lm solar panels with Whether it involves Q-switched DPSS lasers, the high pulse repetition rate and ______drilling, cutting, or scrib- pulse-to-pulse stability of nanosecond micromachining lasers like the Coherent AVIA series are critical to producing clean ing, precision micro- 62 Depot St., Verona, NJ 07044 machining requires ph: 973-857-8380 / fx: 973-857-8381 scribes with the uniform scalloped profi le that is needed for www.innpho.com / [email protected] certain technical reasons. This image shows a “P2” scribe minimization of the heat- performed at 532 nm. affected zone (HAZ),

30 June 2012 www.laserfocusworld.com Laser Focus World

which defines the extent of any thermal damage to the surround- ing material. The HAZ can be minimized by using shorter pulse- GuideStar II widths or shorter wavelengths. Shorter pulsewidths minimize the amount of heat that can escape and spread during the material- The Intelligence Behind removal pulse, which is the reason that most Q-switched micro- machininglasersare designed toproduce pulses of afewtensof Critical Alignment nanoseconds or less. Moreover, in some materials, shorter (ultra- violet) wavelengths enable material removal by direct bond breaking. The high peak output power of Q-switching is an advantage here since it enables efficient harmonic generation to convert the near-infrared (NIR; 1.06 μm) fundamental wavelength to 532 nm,355nm,or even 266nm.Indeed, theoverridingneedto minimize HAZ means that NIR is used in only a few micromachining applications, such as marking, where they offer beam quality and stability advantages over fiber lasers.

Modelocked lasers now very diversified The applications for modelocked lasers are very diverse, indeed far more so than for Q-switched lasers, and can only be briefly surveyed within the scope of this article. Moreover, these disparateapplications aresupported by similardiversity in available laser designs. Femtosecond Ti:sapphire oscillators are widely used as scientific research tools, often in conjunction with regenerative The GuideStar II system – the amplifiers, such as the Coherent Legend series that boosts the answer to laser beam drift peak power to hundreds of gigawatts. These systems are used correction for guaranteed critical in applications such as generation of accelerated particles for alignment on complex systems. high-energyphysics,the productionof intense terahertz pulses, Utilizing two independent time-resolved photochemistry, and even excising single genes in ™ simple organisms. Moreover, cutting-edge femtosecond oscilla- New Focus picomotor actuated mirror mounts, the GuideStar II torsandamplifiers now featureoptionalcontrolof the carrier- system provides high-reliability, high-precision compensation of to-envelope phase both laser beam pointing and position drift. Our leading picomotor (CEP)—the rela- actuators offer both manual and active 4-axis control with excellent tionship between passive stability. Two camera sensors provide continuous tracking of laser beam position and proﬁles and a GuideStar II controller FIGURE 3. This enables complete control, position tracking and beam proﬁle z-axis image slice 200 μm information through your own computer. was constructed from a stack of With a host of convenient user-friendly features, the GuideStar II 160 separate x-y system by New Focus is the intelligence behind critical alignment for image slices. It was the most demanding laser applications. recorded using 910 nm two-photon 400 μm For more information please visit: excitation and shows www.newport.com/guidestarII-5 or call 1-800-775-5273 a live mouse cortical neuron transgenically labeled with green fl u o r e s c e n t p r o t e i n 600 μm (GFP). (Courtesy of C. Portera- Cailliau and co- workers, University ©2012 Newport Corporation of California–Los Angeles) 800 μm

Laser Focus World www.laserfocusworld.com

SOLID-STATE LASERS continued

the pulse optical envelope and the phase or delicate materials, since their short frequency tripling outside the laser cavity of the oscillating electric fi eld—enabling pulse duration ensures no HAZ. Current and delivers a repetition rate greater than generation of attosecond x-ray pulses via applications include various scribing 80 MHz, which appears completely CW high-harmonic generation (HHG). processes for solar panels, patterning of even at the fast scan rate of this cutting- In biology, compact, closed-box organic LED (OLED) displays, cutting edge application. Ti:sapphire oscillators and wavelength the next generation of medical stents, The fl exibility of Q-switching and extension accessories, such as optical and precision drilling of thin glass for mode locking enables the laser industry parametric oscillators (OPOs), are now smart phone touchscreens, to name to provide a diverse selection of pulsed widely used as turnkey sources that just a few (see article by C. Moorhouse, lasers for an ever wider range of scien- enable nonlinear microscope imaging “Picosecond laser enables new high-tech tifi c and industrial applications. This is of live tissue. These imaging modalities devices,” Industrial Laser Solutions, possible because the versatility of these include multiphoton excitation (MPE) May 2012; http://bit.ly/JEWzZD). techniques allows them to be used in and harmonic-generation microscopy In a quite different application, laser numerous laser types including DPSS, (see Fig. 3). direct imaging (LDI) is a fast-grow- Ti:sapphire, and fi ber lasers. A particularly high growth area is the ing technique for producing high-den- use of ultrafast laser pulses for micro- sity multilayer PCBs. Here, the laser is Marco Arrigoni is director of marketing, Scientifi c Laser Segment,Magnus and nanomachining. In particular, the used to directly write a pattern in a layer Bengtsson is director of strategic marketing, combination of modelocked technology of photoresist. The application nomi- and Matthias Schulze is director of marketing, with fi ber-laser technology has enabled a nally requires tens of watts of CW or OEM Components and Instrumentation, at new generation of amplifi ed picosecond quasi-CW UV laser power in a low- Coherent Inc., Santa Clara, CA; e-mail marco. [email protected]; www.coherent.com. lasers (such as the Coherent Talisker) noise TEM00 beam. This need is met by that offer a choice of NIR, visible, and mode locked Nd:YVO4 lasers operating UV outputs. This type of laser is prov- in the picosecond regime. The high peak Tell us what you think about this article. Send an e-mail to [email protected]. ing ideal for machining fi lms of thin and/ power of modelocking enables effi cient *= 0* 809$:4$;4$ 6! <040* 8>: 040*

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32 June 2012 www.laserfocusworld.com Laser Focus World

LOW-LIGHT IMAGING

Scientific InGaAs FPA cameras heighten sensitivity for NIR imaging

RAVI GUNTUPALLI and MANJUL SHAH

With their high quantum efficiency and In an InGaAs FPA, NIR-optimized CCDs cannot offer sensitivity in the important near- and the 2D array detects sensitivity beyond 1100 nm (see Fig. 1). incident light and shortwave infrared range, deep-cooled, then generates and Scientific InGaAs FPA large-format InGaAs focal-plane-array collects charge; the camera performance cameras have many applications in R&D. ROIC clocks and Commercial NIR cameras incorporat- converts the collected ing InGaAs FPA sensors are typically Imaging and spectroscopy techniques charge to voltage and transfers the designed for use in night-vision and performed in the near-infrared (NIR) resultant signal to off-chip electronics. thermal-inspection applications. Sci- or shortwave-IR (SWIR) region are InGaAs FPAs are typically back-illu- entifi c applications, on the other hand, playing an increasingly important role minated and deliver excellent quan- impose extreme demands on camera in many leading-edge scientifi c and in- tum effi ciency (QE) in excess of 80%. systems to achieve the best possible dustrial endeavors. For instance, in- Currently, many life and physical signal-to-noise ratio (SNR). vestigations in this region are critical science applications use silicon-based As discussed earlier, typical InGaAs to research and development efforts low-light-level CCD cameras for opti- FPAs have sensitivity between 900 and to improve solar cells and semicon- cal imaging and spectroscopy (see 1700 nm. However, great care must be ductors, advance the latest methods table). Although these Si-CCD cam- taken to maximize photon collection of photodynamic therapy, and develop eras provide excellent QE in the ultra- before the incident light reaches the a deeper understanding of stellar to violet-to-NIR range due to silicon’s sensor. For instance, it is important geological landscapes via hyperspec- bandgap properties, even the best to use a single optical window in the tral imaging. Key to achieving higher sensitivity Quantum efficiency (%) in the NIR range (0.9 to 1.7 μm) is 100 the use of sensors based on indium 90 gallium arsenide (InGaAs) focal-plane InGaAs B/I, DD arrays (FPAs). An InGaAs FPA con- 80 sists of a 2D photodiode array—itself 70 comprising an indium phosphide (InP) substrate, an InGaAs absorption layer, 60 and an ultrathin InP cap—that has 50 been indium bump-bonded to a readout integrated circuit (ROIC). 40

FIGURE 1. The quantum efficiency 10 of Si-based CCD sensors and InGaAs FPA sensors is compared. 0 400 600 800 1000 1200 1400 1600 1800 Wavelength (nm)

Laser Focus World www.laserfocusworld.com June 2012 33

LOW-LIGHT IMAGING continued

intellicube® camera, treated with an antirefl ective (AR) coating to maximize photon throughput. One of the particularly noteworthy behaviors of InGaAs FPAs is that their long-wavelength cutoff is reduced when they are cooled. As a rule of thumb, the

Comparing key parameters for InGaAs FPA cameras and silicon CCD cameras

Specifi cations InGaAs FPA Si-CCD Typical pixel size 20 μm2 <8 μm2 to >24 μm2 Typical resolution <1k × 1k 512 × 512 to >2k × 2k Wavelength 900 to 1700 <200 to 1100 response (nm) Typical dark 400 (includes 0.0001 current (e-/pixel/s) ambient background) Fixed pattern noise Present Low

More information at: long-wavelength cutoff shifts by 8 nm for every 10°C of sensor cooling. This phenomenon can actually be advantageous, as the sensor is insensitive to background signal beyond the Wondering how to create a high-end laser shifted far-end wavelength cutoff. In other words, the sensor processing system despite intense cost pressure? acts like a “tunable” low-pass optical fi lter. Use SCANLAB’s intellicube® – the smallest smart Due to a smaller bandgap, InGaAs FPAs are typically dark- scan head with high-performance dynamics. noise-limited devices. For example, commercial InGaAs cameras only offer exposure times up to a few milliseconds, as ® The intellicube combines the advantages of the device saturates due to dark current. In contrast, the use SCANLAB’s successful SCANcube® and intelliSCAN® of deep sensor cooling by scientifi c InGaAs cameras allows scan head platforms: integration times of many seconds. Until recently, this deep cooling required liquid nitrogen; however, scientifi c InGaAs cameras can now achieve cooling down to -90°C via thermoelectric designs. It is important to note that the ambient dark !"#"$ Scientifi c applications impose Want to know if intellicube® is the right scan system extreme demands on camera systems for your application? Contact us at [email protected]. to achieve the best possible

See you at our booth #4C37 at LASYS signal-to-noise ratio (SNR). in Stuttgart, Germany, June 12 -14.

background emission from the sample or experiment also con- tributes to the total dark noise of the detector, so care must be taken to keep the experiment as cold as possible. Advanced camera designs also provide online correction for fi xed pattern noise in InGaAs FPAs. This capability helps preserve uniformity across the dynamic range of the device.

Applications Night vision and surveillance are traditionally the primary www.scanlab.de applications for commercial NIR detectors, but the availability of scientifi c-grade cameras with increased sensitivity is set to advance several key research and industrial applications.

34 June 2012 www.laserfocusworld.com Laser Focus World

The ﬁrst AC kilowatt-hour meter was developed In solar-cell in 1889 by Ottó Bláthy's from Hungary, and has a) inspection, photo- been serving mankind ever since. luminescence (PL) imaging has great potential as an in- line monitoring tool. The ability to utilize this highly sensitive imaging technique during the early stages of the solar cell manufacturing process has signifi- cant ramifications, as PL images of b) ingots, bricks, and as-cut wafers can be predictive of final solar cell efficiency. Designed to MeasMeasureure When 800 nm excitation light is Made for Accuracy applied to multi- crystalline silicon (mc-Si) wafers, elec- Ophir's Revolution in tron-hole pairs gener- Laser Measurement ated by light photons recombine, causing PL emission. In the FIGURE 2. Defects are visible as darker The New BeamTrack Sensor Measures band-to-band wave- regions in band-to-band photoluminescence Power, Beam Position and Beam Size length range (about (PL) images of mc-Si wafers (a). In defect- 1000 to 1200 nm) band PL images of mc-Si wafers, the Tracks for these wafers, the defects are visible as high-intensity regions (b). (Courtesy of S. Johnston, National beam size PL associated with Renewable Energy Laboratory) defects (that is, impu- Measures rities or anomalous material compositions) is weaker due to beam position therecombination ofrelatively fewerelectron-holepairsin the flawed regions. Therefore, defects are perceived as darker in Models from band-to-band PL images (see Fig. 2). In the defect-band wave- 3W to 400W length range (about 1300 to 1600 nm), however, the defect- related sub-bandgap emissions are stronger. Therefore, defects areeasiertoobservein defect-band PLimages.In both imaging methods, scientific InGaAs FPA cameras offer ideal response characteristicsforPLimagingofmc-Si wafers. Most important, researchers have observed linear correlations between defect- band PL images from as-cut wafers (as well as from wafers after several other processing stages) and final solar-cell efficiencies. Another application that requires the sensitivity afforded by scientific InGaAs FPA cameras is the spectroscopy of

nanophotonic materials and semiconductor quantum dots. ______Forexample,RashidZia andhisresearch group at Brown University (Providence, RI) recently used the Princeton Instruments PIoNIR:640, with a 2D 640 × 512 array bonded

Laser Focus World www.laserfocusworld.com June 2012 35

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LOW-LIGHT IMAGING continued Leading the Next Generation of Optical Power Meters 2D NIR spectroscopy

1 Normalized momentum 0

-1

1500 • Drop in Replacement for Legacy 1830-C • USB2.0 (1830-R) and Additional GPIB/RS-232 (1830-R-GPIB) 1550 Interfaces Wavelength (nm) • DC Power Measurements in the 10pW-2 W range

FIGURE 3. Topographical rendering of energy-momentum-resolved • A Chirping Audible Tone for Alignment spectroscopy of a trivalent-erbium-doped yttrium oxide thin-fi lm sample • Hot Swappable Among Detectors highlights the 1535 nm telecom line in the erbium. (Courtesy of R. Zia) Introducing the 1830-R optical power meter, the next generation to a low-noise ROIC, to characterize the wavelength-dependent of Newport’s popular legacy 1830-C model - widely used in fi ber angular emission of various emitters. Zia’s group has captured optic component production and testing. The 1830-R series has spectral data from a trivalent-erbium-doped yttrium oxide thin been completely redesigned, capturing the best functionalities fi lm and highlighted the 1535 nm telecommunications-band light emitted from the erbium (see Fig. 3). This simultaneous and specifi cations you would expect, while taking performance to characterization method requires an imaging spectrograph the next level. The 1830-R is CE and RoHS compliant, features a and a 2D SWIR camera with extremely low noise. high-readability, large 7-segment display and is designed for USB Other key applications of scientifi c deep-cooled, large-format downloadable fi rmware updates. The 1830-R is compatible with InGaAs FPA cameras include nanotube fl uorescence, emission, Newport’s 818 and 918D Series Photodiode Detectors. absorption, semiconductor-failure inspection, nondestructive The 1830-R is the perfect drop-in replacement for your 1830-C testing, hyperspectral imaging, and singlet oxygen imaging. and while it might be time to say goodbye to the old, you

REFERENCES can do so with conﬁ dence with the next generation 1830-R 1. S. Johnston et al., “Imaging study of multi-crystalline silicon wafers optical power meter. To ﬁ nd out more visit Newport at throughout the manufacturing process,” preprint, pres. at 37th IEEE Pho- www.newport.com/1830-R-5, or call 1-800-222-6440. tovoltaic Specialists Conf. (PVSC 37), Seattle, WA, June 19–24, 2011. 2. F. Yan et al., “Defect-band emission photoluminescence imaging on multi-crystalline Si solar cells,” preprint, pres. at 37th IEEE Photovoltaic Spe- cialists Conf. (PVSC 37), Seattle, WA, June 19–24, 2011. 3. T. Trupke and W. McMillan, “Photoluminescence imaging speeds solar cell inspection,” Laser Focus World, 46, 12, 35–41 (December 2010).

Ravi Guntupalli is product manager and Manjul Shah is applications scientist at Princeton Instruments, Trenton, NJ; e-mail: rguntupalli@ princetoninstruments.com; www.princetoninstuments.com.

Laser Focus World www.laserfocusworld.com

Recognizing Photonics Innovators 2012 CLEO/LASER FOCUS WORLD INNOVATION AWARDS

FEATURED AT CLEO:2O12 Conference: 6–11 May 2012 Exhibition: 8–10 May 2012 SAN JOSE McENERY CONVENTION CENTER San Jose, California, USA

WINNER: BioPhotonic Solutions, Inc. Versatility Through Adaptive Optics For the development of femtoAdaptiv™: the first ultrafast laser capable of adaptive pulse self-compression that delivers ultrashort (sub-10 fs) pulses at the focal plane of a microscope objective.

HONORABLE MENTIONS: attocube systems AG Novel Fiber-Based Interferometric Displacement Sensor System For the development of an extremely compact, non-invasive, and multiple- channel interferometric displacement sensor system capable of detecting spatial position change of a device in translational motion with high precision.

Nufern Holmium Doped Active Optical Fibers Enabling High Power 2.1 μm Fiber Lasers For the development of the world’s first high-power silica fiber laser operating at near-IR wavelengths beyond 2.1 μm with more than 60 percent efficiency.

THE INNOVATION AWARDS ARE SPONSORED BY: CLEO:2O12 ®

PHOTONICS APPLIED: MICROELECTRONICS PROCESSING

Ultrafast lasers improve effi ciency of CIS thin-fi lm solar cells

GERHARD HEISE, HELMUT VOGT, ANDREAS HEISS, and HEINZ P. HUBER

While nanosecond laser ablation wafers, with demon- And while nanosecond laser ablation and mechanical scribing patterning strated production and mechanical scribing can be used module effi ciencies of in this process, shorter-pulse picosec- processes for the integrated up to about 13%.2 ond lasers are proving far more suc- interconnects in copper-indium- Many laser pro- cessful in the operation. diselenide (CIS) thin-fi lm solar cells cesses are enabling damage the fi lms through thermal the reliable and effi - Serial interconnection effects and mechanical forces, cient production processes of crystalline and A typical thin-fi lm solar module (about picosecond laser processing offers a thin-fi lm solar cells, 0.5 m × 1 m) is divided into individual much more successful alternative. including junction cells with a strip width of about 5 mm. isolation, laser dop- Thin-fi lm solar cells consist of the ab- The market for photovoltaic (PV) mod- ing, and laser cutting or welding. An sorber layer sandwiched between a me- ules is growing at a rate greater than important technique to enhance the tallic contact and a transparent con- 40% per year.1 Thin-fi lm solar cells con- overall conversion effi ciency of thin- ducting contact through which the tinue to increase their market share in fi lm solar cell modules is through an solar light irradiates the absorber (see the growing solar PV industry. Copper- integrated, monolithic serial inter- Fig. 1). In the substrate confi guration indium-diselenide (CIS)—or more spe- connection that reduces ohmic losses applied to CIS, the metallic contact is

cifi cally Cu(In, Ga)(S, Se)2—thin-fi lm in the module by dividing the large deposited on the glass substrate. solar cells have the potential to achieve modules into smaller cells connected For the monolithic serial intercon- optical-to-electrical energy conversion in series to achieve a high-voltage/ nection, three functional line patterns effi ciencies comparable to bulk silicon low-current output from the module. have to be created in the thin-fi lm layers. The fi rst so-called P1 (pattern 1) n-contact: ZnO has to achieve a galvanic separation of

CIS absorber the molybdenum (Mo) p-contact. In P2, the CIS layer on top of the Mo has to p-contact: Mo be removed to enable a good contact of SiN barrier the Mo to the zinc oxide (ZnO) layer. This ZnO layer is deposited in a later Glass substrate Cell n P1 P2 P3 Cell n+1 process step and acts as the transparent n-contact. The patterning process Interconnecting region P3 separates this n-contact, completing the monolithic serial interconnection. FIGURE 1. A schematic shows the cross-section of the serial interconnect region Mechanically scribed P3 trenches of a CIS thin-fi lm solar cell. The glass substrate is carrying an approximately 1-μm- extend down to the Mo layer; however, thick molybdenum layer followed by a 1–3-μm-thick absorbing CIS layer covered for its functionality, it is suffi cient to by a 1–2 μm zinc oxide layer. The regions labeled P1, P2, and P3 indicate the separate only the conductive ZnO 3 structuring patterns for the monolithic serial connection. layer. The patterns repeat typically every 5 mm, producing a considerable

Laser Focus World www.laserfocusworld.com June 2012 39

MICROELECTRONICS PROCESSING continued

amount of dead area where no electric ing to a lack of selectivity for P2 and power can be harvested. P3.6 Therefore, production commonly Commonly applied structuring pro- employs mechanical scribing for P2 cesses for the integrated interconnects are and P3, which creates 50–70-μm-wide either based on nanosecond laser abla- trenches by chipping off of the CIS or tion for P1 or on mechanical scribing for the CIS/ZnO on top of the Mo. The P2 and P3. Both methods introduce dam- structured lines are irregular and force age to the thin films by thermal effects a large safety distance of 150 to 250 μm. and mechanical forces. Nanosecond- Furthermore, the achievable processing laser-structured P1 is mainly performed speed is limited to about 1 m/s and the with repetition rates of about 100 kHz scribing needles have a limited lifetime. and at process speeds of several meters Much effort in the scientific and per second. Unfortunately due to its lack industrial community is going into of selectivity this process typically intro- research to find suitable laser processes duces some damage.4, 5 to replace mechanical scribing. Using ForP2and P3, the task is more the picoREGEN ultrafast laser from complex, because one layer has to be High Q Laser (Rankweil, Austria; a structured on top of another thin film. Newport Spectra-Physics company) at Nanosecond laser structuring is always a wavelength of 1064 nm with a pulse connected with a thermal diffusion duration of about 10 ps, a repetition length in the range of microns lead- rate of up to 950 kHz, and a maximum

Conventional Picosecond laser ablation FIGURE 2. Patterned patterning structures are Position 1 0.0 compared for the P1 -0.2 monolithic serial interconnections in 30 mm Position 2 -0.4 CIS thin films, showing 1 P1, P2, and P3 lines 0 from top to bottom. P2 -1 Confocal microscope -2 images (left side) show 30 mm -3 commonly applied 1 lines structured by a 0 nanosecond laser (P1) P3 -1 and by a mechanical tip -2 (P2 and P3). Confocal 30 mm -3 imageprofi les(right -100 -50 0 50 100 side) show P1, P2, and P3 lines structured with picosecond laser pulses. The P1 line has been structured from the glass side. The laser lines have typical widths of 30 μm and less visible damage, chipping, and burr compared to the mechanical lines with a width of 50 to 70 μm, requiring a safety distance of 150 to 250 μm between the lines.7 ______Increasing fluence

Laser pulse

30 μm Glass Mo

FIGURE 3. A P1 pattern in molybdenum scribed from the glass side (schematic sketch to the right) is shown with increasing fluence at a scribing speed of 15 m/s (microscopic images with front- and backside illumination). The light blue region corresponds to the exposed buffer layer. The length of the red bars is 30 μm.8

40 June 2012 www.laserfocusworld.com Laser Focus World

power of 30 W, the Laser Centre of the have been scribed with repetition rates P2 scribing Munich University of Applied Sciences up to 950 kHz. We achieved processing The P2 scribe must enable a highly successfully realized all three pattern- speeds up to 15 m/s, limited by the speed conductive contact between the ing steps as demonstrated on 300 × 300 of our scanner system. n-conducting ZnO and the Mo mm2 samples from the R&D pilot line The process window is determined by p-contact. While the P1 process is based at AVANCIS (see Fig. 2). the requirement to separate every cell on single-pulse ablation, P2 trenches are galvanically from its neighbors with- scribed by multipulse ablation at higher P1 processing out damaging the silicon nitride bar- pulse overlaps that accordingly reduce The galvanic separation of Mo is rier layer. Optical microscope images the achievable process speed. A single achieved by irradiating the metal layer show trenches written with increasing 10 ps laser pulse at 1064 nm typically from the glass side (see Fig. 3). This lift- fluence; in some cases, the fluence is too ablates about 100 nm of the CIS layer. off process is based on directly induced low to punch out the Mo. But if the flu- Here, the challenge is to find a suitable laser ablation and utilizes the laser’s en- ence is too high, damage of the buffer combination of the pulse energy and ergy very efficiently, allowing a high- layer below the Mo electrode is visible the number of laser pulses applied at speed structuring process.9 Trenches with backlit illumination. a position to selectively ablate the CIS

a) b)

P3 P2 P1 P3 P2 P1

190 μm 330 μm 50 μm 100 μm

FIGURE 4. Optical micrographs show patterning trenches as applied for the 14.7% efficient module (a) in comparison to the previously used nanosecond laser P1 and mechanical P2, P3 processes (b).11

______

Laser Focus World www.laserfocusworld.com June 2012 41

MICROELECTRONICS PROCESSING continued

down to the Mo layer, avoiding Mo effi ciency improvements of 15–20% damage or CIS residues in the trench. over conventional structuring processes The threshold value measured for have been achieved in the successful CIS ablation with 10 ps laser pulses is cooperation between AVANCIS and the in the range of 0.1 J/cm², but this value Laser Centre in Munich. In September depends strongly on the detailed com- 2011 a record effi ciency of 15.8% for CIS position of the absorber layer, which modules was achieved using picosecond will vary with the manufacturing pro- lasers for P1 and P2 patterns. cess in use. We found that a repetition rate of 950 kHz at a process speed of ACKNOWLEDGMENTS This work was funded by the German Feder- 4 m/s achieved a scribe without caus- al Ministry for the Environment, Nature Con- ing thermal damage. Furthermore, the servation and Nuclear Safety within the proj- electrical contact of the Mo to the ZnO ect “SECIS” under grant No. 0325043A/B. was improved signifi cantly compared to We thank all members of the Laser Centre 10 in Munich who contributed to the success of mechanically scribed P2 trenches. this work.

P3 patterning REFERENCES For P3 patterns scribed with ultrashort 1. “EPIA Global Market Outlook for Photovoltaics until 2015”; www.epia.org/publications/epia-______laser pulses, it is advantageous to sepa- ______publications.html. rate only the conductive ZnO layer. Like 2. M.A. Green et al., Progress in Photovoltaics: Re- P1 from the glass side, this P3 patterning search and Applications, 19, 5, 565–72 (August is also an induced laser ablation process 2011). 3. G. Heise et al., Appl. Phys. A: Mat. Sci. and Pro- with low pulse overlap and no interac- cessing, 104,1, 387–393 (2011). tion between the single pulses. A scrib- 4. V. Probst et al., Solar Energy Mat. and Solar ing speed of 15 m/s has been achieved for Cells, 90, 18–19, 3115–3123 (2006). 5. B. Dimmler et al., Conf. Record of the IEEE Pho- this process. Contrary to P1, the under- tovoltaic Specialists Conf., Lake Buena Vista, FL, lying CIS is the absorbing partner and 189–194 (2005). the ZnO is the transparent partner. The 6. A.D. Compaan et al., Opt. and Lasers in Eng., laser ablation of the ZnO layer is indi- 34, 1, 15–45 (2000). 7. G. Heise et al., Progress in Photovoltaics: rectly induced by the underlying CIS. Research and Applications online, (2012); Compared to single cells, the effi - doi:10.1002/pip.1261, or http://onlinelibrary. ciency of thin-fi lm solar modules is wiley.com/doi/10.1002/pip.1261/abstract. partially reduced by the area lost for 8. G. Heise et al., Applied Phys. A, 102, 1, 173– 178 (2011). the serial interconnection. All laser 9. G. Heise et al., Physics Procedia, 12, B, 149–155 patterning is a means to reduce the (2011). so-called dead area of solar modules. 10. T. Dalibor et al., 26th European Photovoltaic So- Considering conventional mechani- lar Energy Conf. and Exhibition, paper 3CO.2.1, Hamburg, Germany, 2407–2411 (2011). cal patterning processes for P2 and 11. H. Vogt et al., 26th EUPVSEC, Hamburg, Ger- P3, the active area of monolithically many, paper 3DV.2.9 (2011). integrated solar modules is reduced by about 100 μm per cell as a result of Gerhard Heise is senior scientist and Heinz the scribe width of the three individual P. Huber is professor for photonics and direc- pattern trenches and the required in- tor at the Laser Centre of the Munich Universi- ty of Applied Sciences (MUAS), Department of between spacing. As laser patterning Engineering Physics, Lothstraße 34, D-80335 avoids chipping adjacent to the trench, Munich, Germany; e-mail: [email protected]; the spacing between P1, P2, and P3 can www.hm.edu. Andreas Heiss is develop- be signifi cantly decreased resulting in ment engineer and Helmut Vogt is project manager at AVANCIS GmbH & Co. KG, Otto- more active area and increased short- Hahn-Ring 6, D-81739 Munich, Germany; circuit current (see Fig. 4). www.avancis.de. With the gain of active area and the

______optimization of the contact from Mo Tell us what you think about this article. Send an to ZnO in the P2 process, signifi cant e-mail to [email protected].

42 June 2012 www.laserfocusworld.com Laser Focus World

SPECIALTY FIBER

High-saturation-energy Yb fi bers pump up pulsed fi ber lasers

MICHEL BÉGIN and BERTRAND MORASSE

A 40 W, 2 mJ pulsed fi ber laser based Optical fi ber of low-cost and high-brightness fi ber- on an ytterbium (Yb)-doped glass matrix considerations coupled semiconductor pump diodes for fi ber lasers that emit light in the 0.9–1.0 μm absorp- with high saturation energy solves Silica-based optical tion band of Yb DCOF is making the many of the limitations associated fi bers are particular- use of fi ber lasers even more attractive. with traditional Yb-doped fi bers while ly popular as a gain Choosing the best gain fi ber to meet presenting several other advantages. medium because of performance and cost requirements is their excellent beam of the utmost importance when design- New materials processing applica- quality, large heat dissipation, high ing a high-energy/high-peak-power tions in the industrial, medical, or power handling, and robustness, giv- pulsed fi ber laser. Due to its long inter- solar markets require pulsed lasers ing them a signifi cant advantage over action length, a DCOF fi ber is prone with high energy and high peak pow- traditional gas or crystal-based lasers. to nonlinear effects such as stimulated er. To address these new opportuni- For lasing in the 1 μm window, Raman scattering (SRS) and self-phase ties, changing market conditions Yb-doped fi bers are used given their modulation (SPM) that must be prop- have increased the pressure on laser high effi ciency, high doping concentra- erly managed.1 In a master oscillator manufacturers to reduce prices and tion, and wide pump absorption band. power amplifier (MOPA) configu- come up with more innovative and Furthermore, a double-clad optical fi ber ration, the semiconductor seed laser cost-effective technologies. As such, (DCOF) confi guration allows a large has modes with narrow-wavelength fi ber lasers have shown great promise amount of power from low-brightness, linewidths that can create stimulated over the last few years and are Brillouin scattering (SBS) during increasingly capturing market the amplifi cation process that share from solid-state and car- must be suppressed adequately

bon-dioxide (CO2) lasers. for reliable system operation. Pulsed fi ber lasers for materi- To reduce these nonlinear als processing applications at a effects, the choice of the active wavelength near 1 μm have typ- fi ber is therefore critical. Gain ically relied on ytterbium (Yb)- fibers with the following doped silica glass. But the design characteristics and corresponding of high-energy pulsed fi ber lasers attributes are desirable: high presents many challenges that saturation energy for lower pulse cannot be easily overcome with deformation and higher nonlinear traditional Yb-doped optical effect threshold; high pump fi bers. Fortunately, high-energy absorption allowing shorter fi ber pulsed fi ber lasers based on new lengths for higher nonlinear effect Yb-doped fi bers made from a high-sat- high-power pump diodes to be coupled threshold; high effi ciency for reduced uration-energy glass matrix solve many in the DCOF fi ber cladding, allowing pump power budget and reduced heat- of the limitations associated with tradi- the high-brightness signal to be ampli- management issues; stable long-term tional Yb-doped fi bers, while simulta- fi ed to high power levels in a small core output power to reduce degradation neously offering additional advantages. with high beam quality. The availability from photodarkening effects; and

Laser Focus World www.laserfocusworld.com June 2012 43

SPECIALTY FIBER continued

high-beam-quality output. the Yb concentration. The latter, how- peak powers that will lower the nonlin- Looking at these parameters, one can ever, typically comes with increased pho- ear effect threshold. It is well known that see that some tradeoffs are necessary. For todarkening effects. nonlinear effects can be reduced through instance, high saturation energy comes various pulse-shaping schemes of the seed with a larger core diameter that is usu- Traditional Yb-doped fibers diodesignal. However, arbitrarypulse ally detrimental to beam quality. High At high pulse energy (>50 μJ), pulse defor- shapes may be easy to produce at the absorption can be achieved with either mation can severely limit the desired out- seed diode level but will be much harder a larger core diameter or by increasing putpulse shape andcreate unwanted high to preserve when amplified at high output

a) Seed Power amplifier b) Output signal at 1064 nm (W)

DCF-YB-30/250P-FA 40

30 Slope efficiency = 73%

1 W Q-switched oscillator 20

0 0204060 80 Launched pump power at 915 nm (W) c) Relative amplitude (dB) -30 FIGURE 1. A high-power (40 W), high-energy (2 mJ) fiber laser built from high-saturation-energy, 30-μm-diameter -40 ytterbium fiber uses a 1 W Q-switched fiber laser oscillator seed operating at a repetition rate of 20 kHz -50 and a pulsewidth of 80 ns (a). At a 17 kW peak power, the power amplifier operates with a slope efficiency of 73% -60 with respect to the launched pump power at 915 nm (b). Because high-saturation-energy fibers are less affected -70 by nonlinear effects, the output spectrum of the fiber laser shows very little Raman scattering (c). 900 950 100010501100 1150 1200 Wavelength (nm)

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energy. When the amplifi cation reaches High-saturation-energy the saturation energy of the power ampli- glass matrix fi er, the leading edge of the pulse depletes Another solution is to lower the cross-sec- the gain and there is no amplifi cation left tion parameters of the gain fi ber, which for the remaining part of the pulse. depend on the glass matrix used. The use HIGH VOLTAGE This phenomenon has been reported of a different glass host is particularly at- Over 2500 Std. Models in fi ber amplifi ers by several authors and tractive since the Yb cross-sections may Surface Mount and Thru-Hole is due to the saturation energy of a gain be up to two times lower than for tradi- medium, which is calculated with the tional glass fi ber while preserving the ex- DC-DC Converters following formula: cellent mechanical and thermal properties ͞λ of pure silica glass. It is also noteworthy to 2V to 10,000 VDC Outputs (hco o)A mention that the spliceability to standard Esat = –––––––––– Low Profile / Isolated (σ + σ )Γ silica glass fi ber is not affected. Up to 10,000 Volts Standard e a For example, a 20-μm-core fi ber may Regulated Models Available

where h is the Planck constant, co is the have a saturation energy around 0.35 mJ λ speed of light in vacuum, o is the wave- with a different glass host—more than length of the signal in vacuum, A is the twice the value obtained with the silica fi ber core area, Γ is the portion of the sig- glass used in traditional Yb-doped fi bers. nal mode profi le that overlaps with the Other glass matrices could be used such σ σ Yb ions, and e and a are the emission as germanosilicate or fl uoride glass but and absorption cross-section at the sig- the photo-induced or mechanical prop- nal wavelength, respectively.2-6 erties are then less attractive. An alterna- For a fi ber with 20-μm-core diameter tive is the FA series of Yb-doped fi bers operated at 1.06 μm and with an over- made from a high-saturation-energy lap factor near 1, the saturation energy is glass matrix, with different core/clad about 0.15 mJ for a traditional glass fi ber. diameters to suit various high-power This means that any amplifi cation close to pulsed fi ber laser applications (see table). or beyond 0.15 mJ will distort the pulse. alog immediately Though fi ber amplifi ers give excellent Experimental results See PICO’s full cat beam quality and easy integration, the A high-energy (40 W), high-power (2 mJ) www.picoelectronics.com small core area quickly limits the satu- fi ber laser built using CorActive’s DCF- ration energy of the system. Not much YB-30/250P-FA optical fi ber employs fl exibility is possible for increasing the a 1 W Q-switched fi ber laser oscillator High core area without degrading the beam seed operating at a repetition rate of 20 Power quality or compromising fi ber integra- kHz and a pulsewidth of 80 ns (see Fig. tion and packaging. 1). Although the peak power achieved Up to 350 VDC Outputs (Units up to 150 Watts) Specs for FA Series of Yb-doped high-saturation-energy Regulated / Wide Input Range optical fi bers from CorActive Isolated Outputs Core Pump Core Clad numerical absorption Model dia. dia. Application aperture @ 915 nm (μm) (μm) (NA) (dB/m)

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Laser Focus World www.laserfocusworld.com June 2012 45

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SPECIALTY FIBER continued

was 17 kW, the maximum attainable peak power for this fi - ber could be higher than 40 kW without signifi cant Raman When it comes to damage threshold scattering, which is fairly high for a 30-μm-diameter gain fi - ber. The maximum peak power is dependent on the pumping 20W 20J/s scheme, pump wavelength, and delivery fi ber length, and the power amplifi er operates with a slope effi ciency of 73% with respect to the launched pump power at 915 nm. Compared to standard optical fi bers, high-saturation-energy fi bers are inherently more robust against nonlinear effects. As seen on the output spectrum plot, the signal from the 40 W/2 mJ power amplifi er shows very little Raman scattering. Other nonlinear effects such as SBS and SPM will also be decreased using high-saturation-energy fi bers since most nonlinear effects are directly proportional to the peak power propagat- ing in the fi ber. Fibers having a higher saturation energy and lower peak power therefore mitigate these fi ber nonlinearities.

Beam quality High power CW and pulsed laser systems have The glass matrix properties of high-saturation-energy fi bers tend distinct requirements that can’t be met with a to create a high numerical aperture (NA)—typically up to 0.20. one-size-ﬁts-all approach. The NA can, however, be lowered using a pedestal-type fi ber Call us to talk about optics made for your needs. design, which consists of adding a raised refractive-index area around the core to decrease the effective NA (see Fig. 2).7, 8 A pedestal design for high-saturation-energy fi bers offers the

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SPECIALTY FIBER continued

following advantages: increased doping High NA Reduced NA levels for higher pump absorption; an increased mode area for an increased nonlinear effect threshold; a reduced Refractive Core NA index Core NA number of modes for improved beam quality; generation of less amplified stimulated emission to reduce the self-lasing Standard design Pedestal design effect; and good spliceability to standard fiber for low-loss (<0.1 dB) splices. FIGURE 2. The numerical aperture of a high-saturation-energy optical fiber can be reduced The core NA of high-saturation-energy by using a pedestal-type refractive-index design. fibers with a pedestal design is typically decreased to a value near 0.10. But we have found that reducing the NA down Beam diameter (μm) to levels of 0.06 is not advantageous. In FIGURE 3. Beam 1400 I fact, the use of low-NA, large-mode- quality is excellent 1200 area (LMA) fibers (large core diameters (M2 <1.4) and A2 A1 1000 and lower core NA) limits the number Gaussian-shaped using high- 800 of supported modes and they are usu- M2 <1.4 saturation-energy 600 ally operated under tight coiling condi- CorActive DCF- tions to eliminate higher-order modes YB-30/250P-FA 400 and achieve quasi-singlemode operation. optical fi bers. 200 Becausethis tight fiber coilingisoften 0 not highly repeatable and difficult to con- 250 350 450 550 trol in a production environment, high- Position (mm) Cooled CCD Cameras

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48 June 2012 www.laserfocusworld.com Laser Focus World

NA, multimode, high-saturation-energy fi bers are preferred to achieve effi cient singlemode operation but without unfavor- able tight fi ber coiling. The singlemode operation is realized by matching the fundamental mode of the high-saturation energy- fi ber to the fundamental mode of the delivery fi ber. High-saturation-energy Yb-doped glass fi bers offer few nonlinear effects, high effi ciency, and a low M2 value of less than 1.4 with a Gaussian beam profi le, making them an excellent choice for the design of high-energy, high-peak-power fi ber lasers (see Fig. 3).

REFERENCES 1. G.P. Agrawal, Nonlinear Fiber Optics, Academic Press, San Diego, CA (2001). 2. K.T. Vu et al., Opt. Exp., 14, 23, 10996–11001 (2006). 3. D.N. Schimpf et al., Opt. Exp., 16, 22, 17637–17646 (2008). 4. M.N. Zervas et al., “High peak power, high rep-rate pulsed fi bre laser for marking applications,” Proc. SPIE, 6102, 61020Q-1 (2006). 5. F. He et al., Opt. Exp., 14, 26, 12846–12858 (2006). 6. A.E. Siegman, Lasers, University Science Books, Sausalito, CA (1986). 7. P. Laperle et al., “Yb-Doped LMA Triple-Clad Fiber Laser,” Proc. SPIE, 6343, 63430X-1 (2006). 8. P. Laperle et al., “Yb-Doped LMA Triple-Clad Fiber for Power Amplifi ers,” Proc. SPIE, 6453, 645308-1 (2007).

Michel Bégin is a product line manager and Bertand Morasse is an R&D scientist at CorActive, 2700 Jean-Perrin, suite 121, ______Québec, QC, Canada, G2C 1S9; e-mail: [email protected]; www.coractive.com.

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PHOTONIC FRONTIERS: BEAM COMBINING

Beam combining cranks up the power

JEFF HECHT contributing editor

Coherent and wavelength beam power record and is beams that are getting serious consider- combining have multiplied their output under development ation for useaslaser weapons. “Beam for laser weapons. brightness at the source is of limited power in the past few years, reaching importance when considering realistic kilowatts both from coherently combined Incoherent beam [directed-energy] propagation scenar- fiber lasers and from wavelength beam combining for ios in turbulent atmospheres,” wrote combination of diodes. raw power Phillip Sprangle of the Naval Research Monolithic arrays of Laboratory (Washington, DC) and col- Fiber and diodelaserscangenerate im- semiconductor diode lasers are the most leagues in 2008.2 Fiber laser arrays pressive powers from small volumes, established example of incoherent beam are living up to that promise. The US but nonlinear losses, thermal effects, combining. The beams from many laser Navy assembled an array of six 5.5-kW and optical damage limit the output stripes combine in a broad high-power industrial fiber lasers to produce the from a single laser aperture. Combin- beam that is not strongly directional 33 kW Laser Weapon System (LaWS), ing the outputs of many laser aper- but is valuable for laser pumping and which in 2010 engaged representative tures can overcome those limitations. applications such as heat treating that targets over the water at a distance of The simplest approach is incoher- do not require high directivity. one nautical mile. Encouraged by those ent beam combining, which directs Incoherent combination of the tests, the Navy is scaling LaWS to the many laser beams in the same direc- high-quality beams from fiber lasers 100 kW range, with completion tar- tion,increasing totalpower but can generate much more directional geted in 2014.3 not increasing the beam brightness. More sophisti- DOE Isolator SCOWA cated techniques can raise Seed Double-pass current brightness. One is combin- laser SCOWA array drivers ing beams coherently, so their amplitudes add con-

structively. An alternative is SPGD combining beams of differ- controller ent wavelengths, as in wavelength-division multiplexing, which avoids the complexi- Power Near-field Far-field ties of phase matching but detector camera camera produces wider-band laser emission.Bothapproaches have produced markedly FIGURE 1. In first stage of Lincoln Labs’ coherent beam combination system, output of a seed laser is split and amplified by 21 channels of a SCOWA array, and part of the output is higher powers since Laser sampled to a phase controller using a stochastic-parallel-gradient-descent (SPGD) algorithm Focus World last reviewed that feeds back to the SCOWA array. The output then is divided among 11 parallel SCOWA 1 the fi eldfouryears ago. arrays (not shown), which further amplify the output and are then coherently combined. But so far, incoherent beam (Courtesy of MIT Lincoln Laboratory; reused with permission4) combining still holds the

50 June 2012 www.laserfocusworld.com Laser Focus World

Diode coherent mode profi les on a 200 μm pitch, as how many elements we can control,” beam combining shown in Fig. 1. A double-pass through says Fan. The fundamental limits are Coherent beam combining resembles the amplifi er array produced 21 parallel not clear, he adds; “one way to prove phased-array radar—an array of emit- beams, which were monitored to gen- how far you can go is experiments.” ters transmitting in phase to generate a erate phase locking signals. Then a sec- coherent output. In principle, operating ond diffractive optical element, aligned Diode wavelength the emitters in phase and combining their orthogonally to the fi rst, divided each of beam combining beams properly can generate a steerable those 21 parallel outputs into 11 parts, Wavelength beam combining (WBC) beam, but so far most effort has gone to one for double-pass amplifi cation of can generate much higher powers and combining the outputs. each of 11 parallel SCOWA arrays. That brightness levels from diode lasers; in Diode coherent beam combination produced phaselocked output from 218 January 2012, TeraDiode (Littleton, was demonstrated with up to 900 laser of the 231 stripes in the second-stage MA) reporting reaching 2 kW at Pho- stripes in the 1990s, but the need for SCOWA arrays; the remaining 13 tonics West.5 “That demonstration singlemode output and tight phase- stripes did not work. Phase control over shows that direct diodes can produce locking requirements limited output to that large number of elements was cru- the same kind of brightness as the best 5.5 W. New techniques and the use of cial for success. “We’re trying to push fi ber lasers, making them suitable for master-oscillator sources to industrial applications,” says Diffraction Lens drive many parallel amplifi - grating Parviz Tayebati of TeraDiode. ers have overcome those limi- Moreover, the intrinsic wall tations. Last year, Tso Yee Fan plug effi ciency is quite high, and colleagues at MIT Lincoln reaching 46% for recent proto- Laboratory (Lexington, MA) type systems. produced 38.5 W continuous Diode laser Their approach is based on wave from an array of 218 array the external cavity design shown individually addressable slab- in Fig. 2, which places a diode Output coupled-optical-waveguide coupler array within an external cavity (semiconductor) amplifiers containing a transform lens, a (SCOWAs).4 FIGURE 2. Implementation of wavelength beam combination diffraction grating, and an out- with a linear diode array contained in an external cavity. All diode First, a diffractive optical put coupler. The external cavity stripes have the same gain bandwidth, but the external cavity element split the seed laser selects different oscillation wavelengths, shown as red, green, optics are aligned to select a dif- beam into 21 outputs, and and blue, and then combines them into a single output. TeraDiode ferent oscillation wavelength in delivered them to parallel used this approach with passively cooled diodes. (Courtesy of each laser stripe, closely spaced amplifi ers with large circular TeraDiode; reused with permission5) across the diode’s 40 nm gain

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+ , - "# $ "# % ! (# !! !! . " "# &'( PIEZO NANO POSITIONING '() "$* %

Laser Focus World www.laserfocusworld.com June 2012 51

BEAM COMBINING continued

High Performance band centered at 970 nm. The angles high spectral brightness and allows select and stabilize the wavelength. The phase adjustments for beam steering or Lasers by Cobolt. combined output has a bandwidth of atmospheric compensation. Wavelength about 30 nm and can be coupled into beam control is simpler to implement free space or into a beam-delivery fi ber. but produces a broader spectrum, so TeraDiode is now commercializing its it is best suited for applications requir- WBC technology with the goal of beta ing raw power delivery where spectral availability in late 2012. The design is brightness is not important. based on a multiwavelength module Fiber laser beams can be combined that can deliver about 500 W continu- coherently by tiling output of an array of ous wave and can be stacked together phaselocked lasers (or amplifi ers) across to generate powers to about 6 kW. “In an aperture, or arranging transform a recent demonstration supported by optics and a diffractive optical element DARPA we demonstrated 360 W with to fi ll an aperture with light from a more 04-01 Series a Beam Parameter Product (BPP) of 0.6 widely spread array of fi ber emitters, as Compact SLM DPSSLs comparable to singlemode fi ber laser shown in Fig. 3. The Lincoln-Northrop 457, 473, 491, 515, 532, 561, 594 nm technology. Our product introduction group found that tiling concentrated CW power up to 300 mW, rms<0.25% will provide a more tame BPP of 2 to 8 58% of the total power in the desired as required by major cutting and weld- central lobe for inputs to 4 kW. In the- 05-01 Series ing markets,” says Tayebati. Brightness ory, tiling should increase the on-axis High power single frequency DPSSLs levels are comparable to those of indus- intensity by a factor equal to the square 355, 491, 532, 561, 660, 1064 nm trial fi ber and CO2 lasers, and about of the number of emitting elements, but CW power up to 2000 mW, rms <0.1% 10 to 100 times that of standard high- they found that tiling with eight emitters power diode lasers. increased only by a factor of 64, indi- MLD Series cating beam combining effi ciency of Compact diode laser modules Fiber laser beam combining 78%.7 Using the same fi ber laser array, 405 - 660nm Diffraction-limited fi ber lasers can reach feed laser, and phase-control system Fast and deep direct modulation multikilowatt powers, but further pow- with the aperture-fi lling approach and Fully integrated control electronics er increases are constrained by thermal a fi ve-element diffractive optical element, limitations and nonlinear effects such as they reported beam combining effi ciency stimulated Brillouin scattering. Beam of 79% at maximum power of the fi ve • Fluorescence imaging combining offers a faster and simpler beams used. and analysis route to higher powers. Beams can be They also tested wavelength beam • Raman spectroscopy combined incoherently by mixing fi ber- combining with six of the same fi ber • Interferometry laser outputs in large-core multimode fi - lasers used in the coherent tests, but • Semiconductor metrology bers, producing continuous outputs to with seed lasers at different wave- 50 kW. But coherent or wavelength beam lengths, fi ve spaced 0.4 nm apart and combining promises the higher bright- the sixth offset by 0.8 nm. The opti- HTCure™ manufacturing ness and better beam quality needed for cal confi guration was similar to that for ultra-robust lasers and many applications. shown in Fig. 2 for wavelength beam ensured reliability! A team from Lincoln Labs and combination of diodes. With that Northrop Grumman Aerospace arrangement they reported 2.51 kW Meet us at the 12th ELMI Meeting Systems (Redondo Beach, CA) have output and 92% combining effi ciency. and at Cyto 2012, booth n. 512 compared coherent and wavelength All three experiments yielded near-dif- beam combination with commer- fraction-limited output. cial 500 W ytterbium-fi ber lasers.6 Coherent combination was harder to Outlook for beam combining implement because it requires phase Other developers are working on a www.cobolt.se control to within a small fraction of a wide range of variations on the theme

Cobolt Headofﬁce, Sweden wavelength, close path-length matching, of beam combining. At the University of Phone +46 8 545 912 30, E-mail [email protected] narrow laser linewidth, and uniform Central Florida (Orlando, FL), Leonid polarization, they found, but it offers Glebov has used volume Bragg gratings

52 June 2012 www.laserfocusworld.com Laser Focus World

a) b) Transform optic DOE Power in Lens array Output central lobe ∝ fill factor Output

Fiber array Fiber Combining array loss

FIGURE 3. a) In tiled-aperture coherent beam combination, beams are focused individually to cover the target aperture, with a central peak and side lobes. b) In fi lled-aperture coherent beam combining, a single transform optic focuses them onto a diffractive optical element, which redirects each input into the output beam, with some residual light escaping as loss. (Courtesy of S.J. Augst; reused with permission6)

to coherently combine two fi ber-laser 5. R.K. Huang et al., “Direct diode lasers with power fi ber lasers,” Proc. SPIE, 8237, 823705 comparable beam quality to fi ber, CO , and (2012). beams with 99% effi ciency to generate 2 solid state lasers,” Proc. SPIE, 8241, 824102 9. L. Lombard et al., “Demonstration of co- 8 282 W. Onera, the French Aerospace (2012). herent beam combination of fi ber amplifi ers Laboratory (Palaiseau, France), last 6. S.J. Augst et al., “Coherent and Spectral Beam in 100ns-pulse regime,” CLEO, paper CFE2 year coherently combined 100 ns Combining of Fiber Lasers,” Proc. SPIE, 8237, (2011). 823704 (2012). 10. A. Klenke et al., “Coherently combined CPA pulses from a pair of fi ber lasers with 7. C.X. Yu et al., “Coherent combining of a 4 fi ber laser system delivering 3 mJ femtosecond 95% effi ciency, a challenge because kW, eight-element fi ber amplifi er array,” Opt. pulses,” Proc. SPIE, 8237, 823708 (2012). nonlinear effects can exceed the band- Lett., 36, 2686 (2011). width of the phaselocking controller.9 8. I. Divliansky et al., “Multiplexed volume Bragg Tell us what you think about this article. Send an gratings for spectral beam combining of high e-mail to [email protected]. Coherent combination of beams from a pair of chirped-pulse fi ber amplifi ers has produced 3 mJ pulses with 89% effi ciency.10 Progress is fast, and much remains to be sorted out. All three major approaches show promise, and each may fi nd its own distinct applications. Coherent beam combining promises the best performance but appears the most complex approach. Wavelength beam combining may be easier to implement for many applications. And it will be interesting to see if incoherent combination is good enough for high-energy laser weapons.

REFERENCES 1. J. Hecht, “Photonic Frontiers: beam combining - Combining beams can boost total power,” Laser Focus World, 44, 7 (July 2008). 2. P. Sprangle et al., “High-Power Fiber Lasers for Directed-Energy Applications,” 2008 NRL Review, pp. 88–99; www.nrl.navy.mil/ content_images/08FA3.pdf.______3. R. O’Rourke, “Navy Shipboard Lasers for Sur- face, Air, and Missile Defense: Background and Issues for Congress,” Congressional Re- search Service (Jan. 21, 2011); www.fas.org/ ______sgp/crs/weapons/R41526.pdf. Fermionicss www.fermionics.com 4. S.M. Redmond, “Active coherent beam com- Opto-Technology bining of diode lasers,” Opt. Lett., 36, 909– 4555 Runway St. • Simi Valley, CA 93063 Tel (805) 582-0155 • Fax (805) 582-1623 911 (Mar. 15, 2011).

Laser Focus World www.laserfocusworld.com June 2012 53

ORGANIC PHOTOVOLTAICS

Transition metal oxides increase organic solar-cell power conversion

MARK T. GREINER, LILY CHAI, and ZHENG-HONG LU

Organic solar cells have struggled to of donor and accep- phase and an electrode is critical for achieve high power conversion effi ciency tor molecules form effi cient charge collection and attaining separate phases that high PCEs.1 As charges cross an inter- (PCE); however, transition metal oxides percolate throughout face, a voltage drop can occur, result- can provide a major PCE boost when the device (see Fig. 2). ing in a decrease in PCE. Furthermore, used as electrode modifi ers to improve The blended organic if an electrode is not charge selective open-circuit voltage, short-circuit phases are sandwiched then leakage currents will occur, further 2 current, and fi ll factor. between two electrodes, decreasing the PCE. Cathodes should an anode and a cathode. only collect electrons and anodes only Organic photovoltaics offer an inex- During light absorption, an elec- holes. Voltage drops and leakage cur- pensive alternative to traditional in- tron moves from the highest occupied rents can be minimized by incorporat- organic solar cells. They also allow molecular orbital (HOMO) of a donor ing an appropriate buffer layer between for a fl exible form factor that makes molecule into the lowest unoccupied the electrodes and the organic phases. possible novel portable power applica- molecular orbital (LUMO) of an Transition metal oxides have proven tions and unique fabrication processes, acceptor molecule, leaving behind a to be very useful electrode buffer layer such as roll-to-roll printing (see Fig. 1). positively charged “hole” on the donor materials.3 They allow interfacial These factors may provide the avenue molecule. The electron and hole move energy-level alignment to be tuned to to popularize renewable energy in the in opposite directions toward the two maximize cell voltage and they have rec- consumer electronics market. electrodes. Electrons are collected by tifying properties that decrease leakage Although organic photovoltaics the cathode and holes by the anode. currents. Transition metal oxides exhibit (OPVs) have cost and manufacturing The interface between an organic a wide range of electronic properties that advantages over inorganic PVs, they are hindered by low power conversion effi ciency (PCE). However, recent progress in OPV research has led to substantial PCE gains that are making OPVs commercially attractive. These improvements are largely due to the realization that interface engineering is essential for achieving high-effi ciency OPVs.

Organic PV operating principles In a solar cell, light absorption generates mobile charge carriers that are collected by two electrodes to generate a voltage. In OPVs, organic molecules absorb the light. Typically OPVs FIGURE 1. An organic solar cell can be made out of fl exible plastic, such as this use the bulk heterojunction design. Konarka Power Plastic solar panel. (Courtesy of Konarka) In a bulk heterojunction, a blend

54 June 2012 www.laserfocusworld.com Laser Focus World

can be tuned through their chemical treatments, which makes them very versatile materials.4 Some oxides are suitable as cath- Solutions, ode buffer layers and others as anode buffer layers.

Power conversion effi ciency In a Flash Defi ned as the ratio of outgoing electrical power to the incoming solar power, PCE is the product of three parameters: open circuit ™ 5 voltage (VOC), short circuit current (JSC), and fi ll factor (FF). OptoFlash Optical Engines The VOC is the maximum voltage that a solar cell can generate, JSC is the maximum current it can generate, and FF is a parameter that describes the maximum power it can generate.

All three factors—VOC, JSC, and FF—depend heavily on electrode/organic interfaces. With the incorporation of a metal oxide buffer layer at electrode/organic interfaces, these three factors can be optimized to boost an OPV’s performance.

Energy level alignment and VOC The maximum VOC that an organic solar cell can achieve depends on the offset between a donor molecule’s HOMO and %!!#"&"' an acceptor molecule’s LUMO.6 However, the maximum V OC &# (weight - 30 grams) can only be achieved by appropriately tuning the energy-level to 10 per standard device !* alignment at the electrode/organic interfaces. ! !!$ Energy-level alignment refers to the offset between the HOMO "#$! or LUMO levels and an electrode’s Fermi level. These offsets are now available

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Laser Focus World www.laserfocusworld.com

ORGANIC PHOTOVOLTAICS continued

a) b) c) E Anode Cathode Light V

LUMO LUMO Accept or ph ase EF Buffer D EF o e nor phas HOMO

HOMO

AnodeDonor Acceptor Cathode

Buffer Blended donor and Buffer layer acceptor phases layer FIGURE 2. In a bulk-heterojunction organic photovoltaic design (a), light absorption generates electrons and holes that travel through the

donor and acceptor phases (b), and in the energy level diagram (c), EV represents the vacuum level and EF represents the Fermi level. labeled as ΔHOMO and ΔLUMO, respec- tion energy and the cathode’s work func- metal electrodes because oxides can tively (see Fig. 3). In order to have a zero tion is less than the acceptor molecule’s achieve much higher work functions voltage drop at an interface, the HOMO electron affinity. Consequently, the max- than metals. The highest known metal

(LUMO) level should be in perfect align- imum VOC is proportional to the energy work function is approximately 5.3 ment with the anode (cathode) Fermi level. offset between the donor’s HOMO level eV for platinum (Pt), while the highest At the anodeinterface,ΔHOMO should and the acceptor’s LUMO level. If HOMO known oxide work function is approx- be zero, and at the cathode interface, and LUMO levels are not aligned with the imately7.0 eV for vanadium oxide

ΔLUMO should also be zero. respective electrode Fermi levels, then the (V2O5). Furthermore, the high-work- It was recently shown that metal oxides VOC will be less than the ideal value. function metals are expensive noble met- exhibit a broad spectrum of energy-level Transition metal oxides can be used als—such as gold (Au) and Pt—while the aligning capabilities.7 When an electrode’s to tune electrode work functions in high-work-function oxides are low-cost

Fermi level is below a molecule’s HOMO order to maximize VOC. They are minerals such as MoO3 and V2O5. level, the minimum ΔHOMO is achieved, capableofa wide rangeof workfunc- Metal oxides also have an advantage and when an electrode’s Fermi level is tions. For example, oxides of titanium, over metals for low-work-function elec- above a molecule’s LUMO level, the min- zinc, tantalum, and zirconium—such trodes. The metals that have low work

imum ΔLUMO is achieved. as TiO2, ZnO, Ta2O5, and ZrO2—have functions, such as calcium (Ca) and An electrode’s Fermi level is parameter- low work functions and can be used as magnesium (Mg), tend to be very reac- ized by its work function φ. Work func- cathode buffer layers. Other oxides of tive, and when in contact with organic tion represents the energy lost (gained) molybdenum, nickel, copper, and vana- molecules they will break the molecule’s

when removing (adding) an electron from dium—MoO3, NiO, CuO, and V2O5— chemical bonds. On the contrary, low- a material. The maximum VOC can be have high work functions and can be work-function oxides are chemically achieved when the anode’s work function used as anode buffer layers. inert, such as zirconium oxide (ZrO2) is greater than the donor molecule’s ioniza- Metal oxides have the advantage over and titanium oxide (TiO2).

a) b)HOMO (eV) c) LUMO HOMO E MoO CrO TiO WO V 3 3 3-x 2 3 Cathode Anode MoO2 Cr2O3 TiO1+x W Cathode Mo Cr Ti NiO Anode work work function V2O5 Co3O4 CuO Ta2O5 function 2 V2O5-x CoO Cu2O Ag2O LUMO V Co Cu ZrO EF 2 Max. VOC = EA = IE EF HOMO 1

LUMO = 0 HOMO = 0 Max. V 0 OC AnodeDonor Acceptor Cathode -2 -1 0 12 Electrode work function Work function - IEorg (eV) FIGURE 3. An energy level diagram of a bulk heterojunction photovoltaic device illustrates the cathode and anode work functions, the

HOMO and LUMO offsets (ΔHOMO and ΔLUMO, respectively), and the open-circuit voltage VOC.

56 June 2012 www.laserfocusworld.com Laser Focus World

ORGANIC PHOTOVOLTAICS continued

Leakage current and JSC and FF range of electronic structures—from is approximately 8%. Energy aligning Both JSC and FF are affected by leak- p-type semiconductors to n-type semi- and charge-selective electrode buffer lay- age currents. In a photovoltaic device, conductors (see Fig. 4). Wide-bandgap ers are essential for such high effi cien- if an electrode collects both holes and p-type oxides with high work functions cies. Transition metal oxides are versatile electrons, the result is a decrease in net are ideal anode buffer layers because buffer layers because of their energy- current and a consequent decrease in they allow holes to pass but not elec- aligning and charge selective properties,

JSC and FF. trons. Wide-bandgap n-type oxides and they will continue to play a role in Metallic electrodes are not charge with low work functions are ideal for improving OPV PCE values. selective; oxides can be if they have cathodes because they allow electrons the right electronic band structure. to pass but not holes. REFERENCES 1. W.Z. Cai et al., Solar Energy Mat. and Solar Cells, Transition metal oxides can have a The highest-reported PCE for OPVs 94, 2 (2010). 2. E.L. Ratcliff et al., J. Phys. Chem. Lett., 2, 11 (2011). a)Energy (eV) b) 3. T. Gershon, Mat. Sci. and Technol., 27, 9 (2011). 0 EV 4. M.T. Greiner et al., Nat. Mat., 11, 1 (2012). Conduction bands 5. B. Kippelen and J.L. Bredas, Energy & Environ. Sci., 2 2, 3 (2009). 4 6. R. Po et al., Energy & Environ. Sci., 4, 2 (2011). EF CoO

Cu 7. C. Tengstedt et al., Appl. Phys. Lett., 88, 5, CuO

6 MoO Co Ag Cr 2 NiO 053502 (2006). O 2 3 2 EF O ZrO O O TiO

8 2 3 4 Ta CrO

V Mark T. Greiner and Lily Chai are PhD 2 MoO 2 2 WO 2 O 10 O Valence researchers and Zheng-Hong Lu is professor 3 5 5 bands 3 3 and Canada Research Chair in Organic 12 Decreasing work function Anode buffer layer Cathode buffer layer Optoelectronics, Tier 1, in the Department of Materials Science and Engineering at the FIGURE 4. Schematic electron energy levels are shown for various transition metal oxides that University of Toronto, ON, Canada; e-mail: mark. function as electron-blocking anode buffer layers and as hole-blocking cathode buffer layers. [email protected]; www.utoronto.ca.

Laser Focus World www.laserfocusworld.com June 2012 57

LASERS ■ OPTICS ■ DETECTORS ■ IMAGING ■ FIBER OPTICS ■ INSTRUMENTATION New products Would you like to be included? Please send your product description with high-resolution digital image to: [email protected]

Miniature spectrometer The VS-7000+ mini CCD spectrometer features an uncooled, back-thinned charge-coupled device (CCD) with a deep full well and a USB 2.0 interface. It comes in heights of 300 or 1000 μm and Beam steering is designed for industrial low-light applications. It The GuideStar II mirror-mount-based laser beam covers three spectral ranges: 200–860 nm, 380– steering correction system provides precision control 750 nm, and 200–1050 nm. of laser pointing and position drift. It includes two Horiba Scientifi c independent Picomotor-actuated, motorized mirror Edison, NJ mounts to provide both manual and active four-axis www.horiba.com/vs7000+ control. Two miniature CMOS cameras provide position sensing and continuous tracking of both laser beam positions and profi les. New Focus, a Newport Corp. brand Santa Clara, CA www.newport.com/guidestarii

Motion controller The A3200 Automation Controller option for the Multi-Axis Machine Controller provides a rugged- panel-mount or rack-mount (1U or 4U) computer for industrial environments. Front and top connec- IR cameras tions allow installation with panel-mount High-resolution shortwave-infrared (SWIR) cameras devices, and a 183 × 183 × 70 include the GA1280J military-hardened camera with mm enclosure saves space. 1280 × 1024 pixels, 15 μm pitch, and 60 Hz full frame Optional peripherals include rate. The SULDH2 1024-pixel linescan camera has a FireWire, USB, and serial line rate of more than 91,900 lines/s. The SU640HSX ports; dual Ethernet; and high-sensitivity, uncooled, military-hardened snapshot solid-state storage. video camera has 640 × 512 resolution. Aerotech Sensors Unlimited—Goodrich ISR Systems Pittsburgh, PA Princeton, NJ [email protected] www.sensorsinc.com

58 June 2012 www.laserfocusworld.com Laser Focus World

Bandpass fi lters The BPF Series of terahertz and infrared bandpass fi lters are designed for extreme environments. There are more than 100 standard models, including more than 25 pass bands and four aperture sizes. They have a high ratio

offered, as well as a choice of two or three locking actuators. Newport Irvine, CA of clear aperture area to fi lter size, and www.newport.com/SN200 are made with an ultra-thin gold fi lter ModBoxes layer for minimal weight. Dual-view imaging system • Optical Modulation Units and Lake Shore Cryotronics A dual-view imaging system allows Reference Transmitters • Telecom : NRZ 44 Gb/s, DQPSK Westlake, OH simultaneous view of a single sub- 44 Gb/s, 56 Gb/s, 100 Gb/s [email protected] ject and enables capture of an image • NEW ! : 850 nm NRZ 28 Gb/s at multiple fi elds of view (FOV). It Laser scanning software includes a single objective lens pre- Laser Modeller 3D laser scanning soft- sented to two separate imaging chan- ware can cut 3D modeling time of old nels, which can be fi xed, zoom, or a industrial facilities by half. The software combination of both. Two separate light sources or wavelengths can be used, with minimum potential optical magnifi cation range of 0.09 to 6.13x. Navitar Modulators • 780 nm to 2.0 μm Rochester, NY • Up to 40 Gb/s - 40 GHz [email protected] • High Extinction (up to 40 dB) • Phase and Intensity High-power modules Seven high-power modules for the N6700 modular power system allow test-system integrators and R&D engi- transforms laser scan data into Plant neers to deliver multiple channels of Design Management System models, up to 500 W to devices under test. allowing designers to re-engineer the Features include output changes of facilities. It accepts data from all com- RF Drivers and mercial laser scanning hardware. Modules Aveva • Analog, Digital and Pulse Drivers Manchester, England • Voltage up to 12.5 Vp-p • RF Delay Lines www.aveva.com/AVEVA_Laser_ • D-Flip-Flop Modeller______

Stainless-steel mirror mount The stainless-steel Suprema SN200 0 to 50 V in less than 2 ms and digi- [email protected] series mirror mount for 50.8-mm- tized measurements from mA to 50 A. phone : +33 381 853 180 diameter optics allows unencumbered Agilent access to the edge of the mirror. Right- Santa Clara, CA ______handed or left-handed versions are www.agilent.com/fi______nd/N6700

Laser Focus World www.laserfocusworld.com June 2012 59

New products

Portable methane analyzer turing, process industries, and test and in mass production and deployed in research, it incorporates signal con- live networks worldwide. A portable methane (CH4) analyzer offers parts-per-billion (ppb) preci- ditioning for transducers and offers a Kotura sion in a compact, rugged, crush-proof clear, fi ve-digit display. Monterey Park, CA RDP Electrosense www.kotura.com package. It reports CH4 and H2O concentrations in real time, continuously Wolverhampton, England at user-selectable rates up to 1 Hz. It [email protected] Debris shields for is based on Off-axis Integrated Cavity target-facing optics Output Spectroscopy (OA-ICOS) tech- Hybrid glass light-shaping Debris shields to protect target-fac- nology, a fourth-generation, cavity- diffusers ing optics located in high-power laser enhanced laser absorption technique. Hybrid glass light-shaping diffusers offer facilities use a range of glasses, includ- Los Gatos Research up to 92% transmission from 350 nm to ing BK-7 and fused silica, which offer Mountain View, CA the visible light range. Able to withstand www.lgrinc.com temperatures of 150°C, they are available in various angles and sizes up to Signal conditioner 20 × 20 in. on optical glass or fused The compact E725 signal conditioner silica substrates. Antirefl ective coating and display unit can be used in a on one or both sides is available. stand-alone or panel-mounted mode. Luminit Torrance, CA [email protected]

Low-power 100 Gbit/s homogeneity and transmission from optical engine the UV to the near-IR. Using propri- A low-power 100 Gbit/s optical engine etary techniques, debris shields are supports the interconnect fabric for manufactured up to 600 mm in diame- next-generation data centers and ter, with typical wavefront error of λ/10 Local display of transducer values, high-performance computers (HPC). and surface fi nish of 40/20–10/5. from various sources, include dis- Utilizing WDM technology, the optical Optical Surfaces placement, pressure, load, and torque. engine chips are based on a micron- Surrey, England Designed for applications in manufac- scale manufacturing platform currently [email protected]

S Ωsecurity & surveillance Ωmicroscopy OUR CAMERA ARE NIR PERFECT. Ωlinescan inspection Ωart inspection Ωindustrial process control Ωastronomy Ωlaser beam proﬁ ling Ωsolar cell inspection Ωbiomedical analysis Ωfree space communications SWIR SWIR images Visible view SWIR penetrates fog Ωspectroscopy OCT scan through plastic through fog to show detail At Sensors Unlimited - Goodrich ISR Systems, our near-infrared cameras deliver what thermal imagers can’t – clear, lifelike detection in daylight or low light, with the ability to detect lasers and even see through glass and plastic. Our uncooled shortwave infrared cameras operate at room temperature, and are compact and lightweight. No one comes closer to NIR perfection. Because we know IR. Contact us today. phone: 609-520-0610 email: [email protected] www.sensorsinc.com right attitude/ right approach / right alongside www.goodrich.com

60 June 2012 www.laserfocusworld.com Laser Focus World

New products

Fiber-optic safety DVD A fi ber-optic safety DVD serves as a primer on the safety elements and con- cerns of users working with fi ber-optic Advancing systems, components, fi bers, or instal- Temperature lation. Content includes visual safety for optical light sources and amplifi - Control ers, physical safety for handling optical

Procedure Help fi bers and chemicals, on-the-job train- Calculating optimum servo constants Servo performance ing for those installing optical cables, Analysis complete Offset gain 36.79 s and information on various national Slope gain 4.47 s and international fi ber safety standards. emperature (C) AFL T Duncan, SC 25 30 35 40

sales@afl global.com 0102030405060 Time (s) / Expected servo response Polymer-based optics Optotune has developed fast, elec- Never again spend frustrating hours tuning a P-I-D temperature controller. trically or manually tunable optical The VueMetrix tuning "wizard" will solve your temperature control problems with a few clicks. Integrated with the VueMetrix TEC controller, the wizard will analyze your system and effortlessly produce the correct solution.

devices that use soft polymer-based materials to overcome the limits of hard glass and plastic components, providing an alternative to traditional optics. The range of focus-tunable lenses and The Vue-TEC Developer's Kit contains laser-speckle reducers has applications everything you need to get started. including machine vision, lighting, laser Windows software, DC power processing, ophthalmology, microscopy, supply and mating connectors and laser projection. Volume pricing and packaging Pacer International option available

______Berkshire, England www.pacer.co.uk www.vuemetrix.com Aspheric assemblies 408-734-9974 The 7100141 and 7100143 molded infrared aspheric imaging assemblies are for applications in longwave-infrared thermal imaging. The 7100141 is f/1.2 with 16.74 mm focal length and

Laser Focus World www.laserfocusworld.com June 2012 61

New products

is athermalized. The 7100143 is f/1.3 Patterning laser Thin-fi lm TEC with 10.15 mm focal length. They use The Paladin Advanced 355 24000 The eTEC HV14 thin-fi lm thermoelec- molded chalcogenide infrared aspheric modelocked, diode-pumped, solid- tric cooling module measures 3 mm2 lenses, and are designed for use with state laser delivers over 24 W (at 80 640 × 480 and 320 × 240 sensors. MHz) at 355 nm for high-through- LightPath Technologies put Laser Direct Imaging and other Orlando, FL advanced microelectronics appli- www.lightpath.com cations. It provides a TEM00 beam (M²<1.2), beam pointing stability ArF excimer laser The GT63A ArF excimer laser for multi- patterning immersion lithography includes Spectrum Multi-Positioning for focus drilling, which increases laser and 0.6 mm high, and can pump up to spectrum control for wider depth a maximum power density of 120 W/ of focus. Additional features include cm2 compared to <10 W/cm2 for the the company’s Recycled Chamber bulk TEC. The response time is on the Operation System, Supreme Total Gas <20 μrad/°C, long-term power sta- order of milliseconds. It provides 55°C Manager, and Smart Monitoring for bility of <±2%, and noise <1% rms of cooling performance at an ambient real-time information management. from 10 Hz to 2 MHz. temperature of 25°C. Gigaphoton Coherent Nextreme Thermal Solutions Oyama, Japan Santa Clara, CA Durham, NC [email protected] [email protected] www.nextreme.com

Optically Clear Epoxy EP37-3FLF High flexibility Low exotherm Resistant to thermal cycling and shock

154 Hobart Street, Hackensack, NJ 07601 USA +1.201.343.8983[email protected] ______www.masterbond.com

62 June 2012 www.laserfocusworld.com Laser Focus World

Our VCSEL Key Differentiators: • High power (10~1000W) from a single chip, 6kW from a module • Low Cost (single device, arrays) • LED like surface mount packaging 0 compact, robust device includes dust- • High temperature operation to 95 C proof optical components and uses a • Excellent wavelength stability (<0.07nm/0C) blue LED. It allows partial focus area • Speckle-free illumination-see below examinations of a defect region during • 640, 780, 795, 808, 830, 976, 1064, manufacturing. 1550nm Steinbichler Optotechnik • Custom wavelengths (630~1100nm) Neubeuern, Germany www.steinbichler.com

Microscope illumination The Brightfi eld LED illuminator 2kW-808nm replaces the standard lamphouse VCSEL side and can be fi tted to most modern pumping module

Speckle Free Illumination

upright and inverted microscope Applications: systems. The unit can use manual • Illumination (works like LEDs, but with small size and high efficiency) intensity control, TTL control, or ON/ • Solid-state laser pumping (chips, OFF, eliminating the need for shutter high power modules for end and mechanisms. Intensity can be regu- side pumping) lated manually. LED operating • Sensor applications, single mode lifetime exceeds 10,000 hr. devices (1 to >100mW) and arrays – Prior Scientifi c high volume available Rockland, MA • Automotive- low cost ranging [email protected]

Characterization tool for photovoltaic cells www.princetonoptronics.com PM-QE is designed for character- [email protected] ization of photovoltaic (PV) devices. (609) 584-9696 ext. 107

Laser Focus World www.laserfocusworld.com June 2012 63

New products

It determines spectral glass, and coatings. It can clean solar cells, laser hardware, response (SR, A/W), scientifi c instruments, and high-precision optics. The prod- external quantum effi - uct includes fl uid and disposable, lint-free wipes. ciency (EQE/IPCE, %) and Microcare internal quantum effi - New Britain, CT ciency (IQE, %). PM-QE’s [email protected] light path is through optical fi bers rather than UV-visible forensic lens free-space optics, allowing The Model 228 lens oper- operation over long periods without alignment or moving ates in the UV and visible parts, as well as any effect from environmental light. ranges, enabling forensic ThetaMetrisis scientists to focus on a Athens, Greece target in the visible and [email protected] then slide a fi lter across to take UV images with- Optical out having to refocus. It has a fi eld of view of 8.3° at 1:1.25 cleaning solution magnifi cation up to 16.6° at long object distances. Optixx optical cleaning solution Resolve Optics Ltd. is fast-drying, nonfl ammable, Chesham, England nonhazardous, and plastic-safe. [email protected] It gets rid of soils such as dust, oil, grime, and moisture from Lens design software optics and lenses, metals, plastic, Version 6.6 OSLO lens design software is now fully compatible with Windows 7. Program improvements include STEP fi le export, TOPS merit functions, NotePad++ editor, user- selectable private folder, Q-Type Asphere improvement in the premium edition, and an updated help system. This release also includes updated glass and vendor lens catalogs. `)) !j_ Lambda Research Littleton, MA ( www.lambdares.com q!_K 'q }{q~K"!(_ Nitrous oxide analyzer ! _' q_ The IRIS 4600 mid-IR laser-based nitrous oxide analyzer q! uses mid-IR laser absorption spectroscopy to simultane- _{_! ously measure nitrous oxide and water vapor concentrations, q!q| allowing calculation of the nitrous oxide dry-mole fraction at )_K sub-ppb levels. The analyzer can make measurements in the Y! )__ 50 to 4,000 ppb range. __ Thermo Fisher Scientifi c ! "#$" Franklin, MA )K www.thermoscientifi c.com/ghgmonitoring

______K')K Streak camera *!=)?')K The C11293 streak camera has sensitivity in the near-infra- Y'= VX \V*]^_ red region up to 1650 nm. The photocathode is made of InP/ &Z=VV[ !"#[VX InGaAs and a sensitivity several orders of magnitude higher

64 June 2012 www.laserfocusworld.com Laser Focus World

New products Business Resource Center

Optics / Coatings Manufacturing Used Equipment Lattice Electro Optics, Inc. WANTED Used & Surplus Laser Equipment 1324 E. Valencia Dr. Fullerton, CA 92831 www.latticeoptics.com T: 714-449-0532, F: 714-449-0531 FOR SALE than the S-1 material used in older streak [email protected] New and used lasers including: cameras. It operates at approximately Helium-Neon, Argon, Krypton, OPSL, He-Cd, -100°C with liquid nitrogen cooling. Need optics & coatings? Nd:YAG, DPSS, diode laser modules, etc. Hamamatsu Quality, quick service & any quantity Midwest Laser Products, LLC Bridgewater, NJ 24 hrs turnaround on most optics & coatings P.O. Box 262, Frankfort, IL 60423 [email protected] CUSTOM optics with a lightening quick delivery Ph. (815) 462-9500 FAX (815) 462-8955 One of the largest INVENTORIES in the industry Web: http://www.midwest-laser.com Microchannel plates email: [email protected] A Long-Life, Low Noise performance option is available for a line of micro- Optics / Coatings Manufacturing channel plates. It provides up to a one- Then, challenge us! hundred-fold reduction in background noise, for applications where the back- High power ultrafast laser optics. High damage threshold optics & coatings. ground noise is lower than the detector High damage PBS, high energy beam expanders. Excimer, YAG, CO2 optics. OPO, crystal & laser rod coatings, prisms mirrors, windows, beamsplitters, WAVEPLATES ON DEMAND polarizing optics, waveplates, filters spherical, OptiSource has made a personal commitment to deliver value to our customers. cylindrical & aspheric lenses, Etalons Value equals price plus convenience plus reliability. (0.1mm-20mm thk). We maintain a coated inventory of standard Coating service (1 day) waveplate diameters, wavelengths and AR, DAR, TAR, BBAR, PR, HR, Hybrid, Metallic retardations. WINDOWS, MIRRORS and LENSES are also available. Please call or email for our UV(from 157nm), VIS, NIR, Mid IR, Far IR NEW CATALOG or view the catalog and pricing noise. At 0.01 counts/s/cm2, the dark Catalog matrix at www.optisourcellc.com count level approaches the background Request our free catalog Prompt Response & Service level of cosmic rays. Compare Delivery Quality and Pricing Photonis Ph: 505.792.0277 / Fax: 505.792.0281 Sturbridge, MA www.optisourcellc.com / [email protected] 102 Mountain Park Pl. NW, Ste. #D www.photonis.com Albuquerque, New Mexico 87114, USA

LED fi ber-optic illuminator module The XLM Plus LED fi ber-optic light module provides light output comparable to 180 W xenon sources, with the Put your products where advantages of LED lighting, including your customers are looking to buy. longer lifetime, lower heat output, and Sign up today for almost no UV or IR radiation. Compliant with medical safety standards IEC/EN “Focus On Products” 60601-1 and EN60601-1-2, it is suited for endoscopy, surgical microscopy, and Contact Katrina Frazer at 603-891-9231 headlamp applications. or [email protected] Excelitas Technologies Waltham, MA www.excelitas.com

Laser Focus World www.laserfocusworld.com June 2012 65

Manufacturers’ Product Showcase

Precision Molded Lenses — Infrared Microscope Economical Optic Solutions Made of Glass The Micro Infrared Microscope is a complete non-contact temperature measurement system that includes thermal imaging camera with microscopic and wide-angle lenses, mounting platform, camera and target positioning micrometer stages, thermoelectric heating/cooling platform, and relay Producing aspheres and all other lenses the conventional way output module. can be costly. Precision glass molding enables production Sophisticated of such optics in medium-sized and high batches, beginning software features at 500 pieces and going to tens of thousands at the fraction include image of the cost of conventional manufacturing. In precision glass comparison molding optics are formed from blanks of optical glass, put analysis, hot spot into the molding tool and molded above the transformation detection, pixel temperature (Tg). After cooling, the parts are coated and emissivity correction, thermal movie recording, 3-D view, qualifi ed. Grinding and polishing optics thus become strip chart, line profi le, and histogram. obsolete, with a tangible effect on your budget.

www.fi sba.com www.optotherm.com • (724) 940-7600

Xenics’ compact uncooled InGaAs camera One-year subscription to Effective waste sorting LASER FOCUS WORLD FREE! and early crack detection inside solar cell wafers are some of the sensitive tasks the compact uncooled SWIR camera Bobcat-1.7-320 covers to contribute to green energy. Bobcat-1.7-320 features: • 0.9 - 1.7 μm sensitivity with low noise and low dark current • Ethernet, CameraLink or analog interface for easy system integration • Full control via a powerful and easy-to-use software development framework

Visit us online at www.lfw-subscribe.com or call Customer Service at 847.559.7500

Xenics headquarters Ambachtenlaan 44, BE-3001 Leuven, Belgium Tel +32 16 38 99 00, [email protected], www.xenics.com/bobcat_green_energy

66 June 2012 www.laserfocusworld.com Laser Focus World

Advertiser&web index ADVERTISING SALES OFFICES

AdValue Photonics ...... 41 OptoSigma Corporation ...... 17 MAIN OFFICE 98 Spit Brook Road, LL-1, Nashua, NH 03062-5737 Apollo Instruments, Inc...... 49 OptoTherm ...... 66 (603) 891-0123; fax (603) 891-0574 Senior Vice President & Group Publisher Christine A. Shaw (603) 891-9178 Bristol Instruments, Inc...... 40 Photline Technologies ...... 59 [email protected] Executive Assistant & Reprint Sales Castech, Inc...... 23 Photop Technologies, Inc...... 57 Susan Edwards (603) 891-9224; [email protected] Digital Media Sales Operations Manager Cobolt ...... 52 PI (Physik Instrumente) L.P...... 51 Tom Markley (603) 891-9307; [email protected] Coherent, Inc...... 19 Pico Electronics, Inc...... 45 Ad Services Manager Alison Boyer (918) 832-9369; fax (918) 831-9153 [email protected] Continuum ...... 24 Power Technology, Inc...... 1 Director, List Sales Kelli Berry (918) 831-9782; [email protected] CVI Melles Griot ...... 49 Precision Photonics ...... 47 NORTH AMERICA New England, Eastern Canada & New Jersey Dilas Diode Laser, Inc...... 11 Princeton Optronics, Inc...... 63 Diane Donnelly, (508) 668-1767: fax (508) 668-4767 [email protected] Midwest, MidAtlantic, Southeast Discovery Semiconductors, Inc...... 6 Qioptiq, Inc...... 23, 25, 27 Jeff Nichols, (413) 442-2526; fax (413) 442-2527 [email protected] Edmund Optics ...... 16 Quantronix Corporation ...... 4 West and Western Canada Paul Dudas, (949) 489-8015; fax (949) 489-8037 [email protected] Electro-Optics Technology, Inc...... 10 Roithner LaserTechnik GmbH ...... 55 Inside Sales—Business Resource Center/Classifi ed, Focus on Products, Product Showcase Evans Capacitor Company ...... 28 Scanlab AG...... 34 Katrina Frazer, (603) 891-9231: fax (603) 891-0574 [email protected] Excelitas Technologies ...... C2 Semrock, Inc...... 12 INTERNATIONAL UK and Scandinavia Tony Hill 44-1442-239547; fax 44-1442-239547 Fermionics Corporation ...... 53 Sensors Unlimited, Inc...... 60 [email protected] France, Netherlands, Belgium, Spain, Greece, Portugal, Southern Switzerland Fisba Optik AG ...... 66 Somerville Laser Technology ...... 47 Luis Matutano (Paris) 33-1 3076-5543; fax 33-1 3076-5547 Innovation Photonics ...... 30 Spectral Instruments...... 48 [email protected] Germany, Austria, Northern Switzerland, Eastern Europe, Russian Federation IXYS Colorado ...... 32 Spectrogon US, Inc...... 36 Holger Gerisch 49-8801-302430; fax 49-8801-913220 [email protected] LightMachinery, Inc...... 12, 22 Stanford Research Systems ...... 13 Hong Kong/China Adonis Mak 852-2-838-6298; fax 852-2-838-2766 Master Bond, Inc...... 62 Sydor Optics, Inc...... 14 [email protected] India Rajan Sharma 91-11-686-1113; fax 91-11-686-1112 Newport Corp...... 31, 37, 55, C4 tec5USA ...... 42 [email protected] Israel (Tel Aviv) Dan Aronovic NKT Photonics AS ...... 26 Thin Film Center, Inc...... 64 972-9-899-5813; [email protected] Japan Masaki Mori 81-3-3219-3561; [email protected] NM Laser Products, Inc...... 62 Trumpf, Inc...... 8 Taiwan Diana Wei 886-2-2396-5128 ext. 270; fax: 886-2-2396-7816 Nufern ...... C3 Veeco Instruments ...... 22 [email protected] For all other international sales, please contact: Christine Shaw, Senior VP & Group Publisher OFS Specialty Photonics Division ...... 44 VLOC/Subsidiary of II-VI, Inc...... 20-21 (see contact info. above)

Laser Focus World Copyright 2012 (ISSN 1043-8092) is published 12 times per year, monthly, by OPCO Laboratory, Inc...... 18 VueMetrix ...... 61 PennWell, 1421 S. Sheridan, Tulsa OK 74112. All rights reserved. Periodicals postage paid at Tulsa, OK 74101 and additional mailing offi ces. Subscription rate in the USA: 1 yr. $162, 2 yr. $310, 3 yr. $443; Canada: 1 yr. $216, 2 yr. $369, 3 yr. $507; International Air: 1 yr. $270, 2 yr. $435, 3 yr. $578. Single copy price: $17 in the USA, $22 in Canada and $27 via International Air. Single copy Ophir-Spiricon, Inc...... 35 Xenics ...... 66 rate for March issue which contains a Buyers Guide Supplement: $135.00 USA, $168.00 Canada, $200.00 International Air. Digital edition $60.00 yr. Paid subscriptions are accepted prepaid and only in US currency. SUBSCRIPTION INQUIRIES: phone: (847) 559-7520, fax: (847) 291-4816. (POSTMASTER: Send change of address form to Laser Focus World, POB 3425, Northbrook, IL Optical Building Blocks Corp...... 18 Xi’an Focuslight Technologies Co., Ltd...... 61 60065-3425.) Return Undeliverable Canadian Addresses to: P.O. Box 122, Niagara Falls, ON L2E 6S4. We make portions of our subscriber list available to carefully screened companies that offer products and services that may be important for your work. If you do not want to receive those offers and/or information, please let us know by contacting us at List Services, Laser Focus World, Optical Society of America ...... 38 Zolix Instruments Co., Ltd...... 63 98 Spit Brook Road, LL-1, Nashua, NH 03062. Standard A Enclosure in Versions P3 & P4 GST No. 126813153 Publications Mail Agreement No. 40052420 Laser Focus World is a registered trademark. All rights reserved. No material may be reprinted. This ad index is published as a service. The publisher does not assume any liability for errors or omissions. Bulk reprints can be ordered from Susan Edwards, PennWell, Laser Focus World, 98 Spit Brook Road, LL-1, Nashua, NH 03062, tel. (603) 891-9224; FAX (603) 891-0574, Send all orders & ad materials to: Ad Services Specialist, Laser Focus World, 1421 S. Sheridan, Tulsa OK 74112 Attn. Reprint Dept.; [email protected].

Laser Focus World www.laserfocusworld.com June 2012 67

BY JEFFREY BAIRSTOW Who is going to run the Internet?

For the 2 billion or so users of the mostly US-based nonprofi t entities such we know it is becoming more wide- Internet, the most amazing thing is that as the Internet Corporation for Assigned spread. Take, for example, Consent the World Wide Web (WWW) pretty Names and Numbers (ICANN) and the of the Networked: The Worldwide much runs itself. Or at least it appears Internet Engineering Task Force (IETF). Struggle for Internet Freedom, a new to do so. But there are ominous signs However, the political infl uence of the book by former Beijing-based CNN jour- that this behemoth is attracting politi- WWW has grown dramatically in recent nalist Rebecca MacKinnon (Basic Books, cal attention that could result in crip- years particularly in emerging powers New York, NY, 2012). In her book, pling regulation by individual countries. such as Brazil, India, and China. These MacKinnon makes a case for the politi- Electronic pipes can be turned off or on countries are bringing into question the cal enfranchisement of Internet users. I at will. But is the United Nations the right governing infl uence of the United States fi nd the cover of MacKinnon’s book to body to run this free-wheeling entity? over the Internet. be rather disturbing. The cover shows a You should keep an eye on the By handing over the control of raised arm in the style of “Black Power.” upcoming World Conference on the Internet to the ITU, lesser pow- Hence the concept of “Netizens” for International Telecommunications ers would have the means of chang- popular control of the WWW. This con- (WCIT) to be held in Dubai in December ing their degree and sphere of infl uence. cept is not new. It has been used by the 2012. This conference of the 193 coun- Since each country gets a single vote in populist Electronic Frontier Foundation tries that make up the United Nations the ITU, this would effectively reduce as conceived by Mitch Kapor, founder International Telecommunication Union the power of the current nonprofi ts and former CEO of Lotus Corp. (ITU) has the goal of negotiating a com- and increase the relative power of the On the other hand, writing recently prehensive treaty that will govern inter- emerging countries. in the Wall Street Journal, Information national telecommunications services Although the Clinton Administration Age columnist L. Gordon Crovitz com- worldwide. A detailed agenda for this was instrumental in setting up the exist- mented, “The Internet shows how cre- meeting had yet to be published as of ing crop of semi-public organizations, the ativity can fl ourish when government this writing but the Internet is likely to current administration has shown little governs least. The Web allows permis- loom large (www.itu.int). interest so far in the possible looming sion-less innovation where no one needs The organizations that currently keep clash of international legislation. In fact, an operating license or other authoriza- the Internet largely free and open are the United States has yet to nominate its tion. This doesn’t leave much of a role delegates to the WCIT. Given that this for multinational groups such as the is a major international conference, the U.N., even if some governments are White House could be making a big mis- plotting otherwise.” take in delaying nominations. In my view, the Internet works remark- The recently elected Russian president, ably well today. If it ain’t broke, why try Vladimir Putin, has already spoken out to fi x it? But if the White House does not on the issue of Internet control. “If we get more involved with WCIT, we could are to talk about the democratization end up with an Internet where large sec- of international relations, I think that a tions are under political control. I, for one, critical sphere is information exchange don’t wish to go there. and global control over such exchanges,” If the White House does not said Putin, speaking shortly after his get more involved with WCIT, inauguration. Both the Russian and we could end up with an Chinese governments are likely to support U.N. governance of the Internet. Jeffrey Bairstow Internet where large sections However, there are some signs that Contributing Editor are under political control. awareness of threats to the Internet as [email protected]

68 June 2012 www.laserfocusworld.com Laser Focus World

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High Speed 2.0um Detectors Kinematic Optic Mounts—only $44 each! EOT is offering its ET-5000 series 2.0um photodetectors. These Siskiyou’s IM100 series products feature economy kinematic mounts a rise time of offer exceptional performance <35ps and a fall at a reasonable price. Mounts time of <35ps have precision rolled 80TPI and an operating adjustment screws for wavelength range excellent resolution and tactile of 900-2200nm, feel. 3/8" aluminum back making them ideal for plates have two 8-32 holes for monitoring the output right or left hand installation of Tm and Ho lasers. and full “L” cutaway for Models are available maximum aperture. There with free space or are six models to choose FC/PC input and include their own internal bias supply. from — contact Siskiyou for more details.

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Motion Solutions for Test, Measurement and Visible and Infrared Absorbers Inspection Exciton’s new absorbing dyes, or “absorbers,” can provide selective Aerotech motion systems’ or broadband light unmatched precision, accuracy fi ltering throughout the and durability have made us a visible and near infrared. leader in test, measurement Absorbers with relatively and inspection applications narrow absorption bands, across a wide array of industries. such as those shown Our newest catalog presents in the graph, fi lter out motion capabilities and solutions IR light with low visible in sensor testing, surface color even at high optical profi ling, nondestructive test, densities. They can be semiconductor inspection and used for selective laser metrology, cleanroom and high- wavelength fi lters and vacuum systems and integrated for security applications. Narrowband absorbers can be combined with automation and data acquisition. visible light-absorbing dyes to create sharp cutoff, longpass fi lters. See our website for the latest information. Exciton, Inc. Aerotech, Inc. PO Box 31126, Dayton, OH 45437 www.aerotech.com (p) 937-252-2989, (f) 937-258-3937, www.exciton.com

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Optics for the life sciences

LEE MATHER

OEMs and researchers are driving the life with customers sciences market for optics, with photonics to develop optical compo- applications ranging from ophthalmology to Cellular traffi cking of cancer optical coherence tomography. nents and sys- cells within the vasculature of tems that are a mouse, which was imaged tailored to their using UVP’s iBox Explorer in vivo Some optics manufacturers cite the life specifi cations, with the goal of solu- imager. The imager uses off- sciences market as being a signifi cant tions to help customers yield proof-of- the-shelf achromatic lenses and driver of their business. Optical fi lters concept. To help researchers lower the other single lenses and fi lters to form multielement objectives and maker Semrock (Rochester, NY) states cost of building imaging instrumen- tube lenses that can be mixed that life sciences is the company’s most tation capable of large magnifi cation and matched to provide seven important market today. Edmund Op- ranges, EO has been able to use an as- different magnifi cations. Filter tics (EO; Barrington, NJ), which pro- sortment of standard achromatic lens- combinations were optimized to duces optical components and coatings, es, singlets, and off-the-shelf fi lters to ensure good signal-to-noise ratio says that the life sciences market makes create low-cost, high-performance for each color channel. The GFP- tagged nucleus of the Human up about 20% of its revenue right now, multi-element objectives and tube lens- HT-1080 fi brosarcoma cell can be with plans to expand even further. And es able to compete with high-priced seen migrating downstream from optical components and thin-fi lm coat- objectives from microscopy compa- the injection site, passing the ings manufacturer OptoSigma (Santa nies (see fi gure), as well as save cus- bifurcation of a distal vein (small Ana, CA) comments that the impor- tomers substantial money, says Petra green dot, down and to the right tance of the life sciences industry is evi- Lepke, EO optical market develop- of center) (Image courtesy of UVP) denced by the fact that its top 20 cus- ment manager. continued on pg. 6 tomers are biomedical-related. Other optics manufacturers are beginning to delve into the life sciences market, including Precision Glass & Optics (PG&O; also in Santa Ana, CA), which is beginning to see a steady increase in customers that are in the life sciences industry.

Key customers Original equipment manufacturers and researchers top the list as the largest customers for the optics manufacturers I interviewed—most of which work

www.laserfocusworld.com Summer 2012 Focus On Products ▲ 5

PRODUCT FOCUS: OPTICS continued

Meeting the challenges advanced hard-coated fi lters with optical (ZnSe), silicon (Si), and germanium (Ge) Application of photonics technologies in density greater than 6.0, says Briggs, help- include innovations in coatings and ophthalmology continues to expand, says ing to avoid damaging delicate biological accommodation of narrower bandwidths Lepke, and optics are key for focusing light samples, and removing unwanted light to facilitate noninvasive imaging, according into the eyes to achieve different levels of from the system. to Lepke. Using these types of optics in penetration for applications such as laser- Dan Bukaty, president at PG&O, notes noninvasive imaging helps to diagnose assisted cataract surgery, which cuts with a that as scientists are discovering more and liver disease, read blood glucose levels, laser to get the cloudy eye lens out; topog- more on the nanoscale, optics become even and monitor oxygen in older patients, raphy-guided LASIK, which uses ultravi- more and more important. So, the ability says Michael Gauvin, VP of sales and olet excimer radiation to ablate the front to look at these things with different wave- marketing at optical design fi rm Lambda surface of the eye lens after the outer eye lengths of light provides greater opportuni- Research Corp. (Littleton, MA). Gauvin layer is fi rst partially cut and peeled out ties for optics and optical coatings. “Due adds that they also aid fl ow cytometry and of the way; and optical coherence tomog- to the specifi city and quantifi able nature cell imaging, which investigate cell counts raphy (OCT), which penetrates into the of fl uorescence imaging, optical fi lters and to fi nd diseases, while Michelle Young, retina. Wavelengths ranging from 800– mirrors have risen in performance to meet regional sales manager at OptoSigma, says 900 nm and those around the 1310 nm the market need for optics that provide that they aid in targeted drug delivery and band are used heavily in OCT, according high performance and spectral complexity stem cell research. Finally, laser and LED to Stephan Briggs, product line engineer over an ever increasing fl uorescent probe biomedical devices to eradicate skin cancer at EO. Various near-infrared wavelengths range,” says Nick George, director of prod- and light therapy throughout the body and penetrate the eye differently and allow im- uct marketing at Semrock. George notes DNA sequencing benefi t from inclusion aging of the retinal or corneal region. that the latest optical fi lters have improved of these types of optics, says Young. This Strong fi lters with narrow or broad the sensitivity, resolution, and speed of fl u- trend should increase as the demand for bandwidth, such as dichroic fi lters, enable orescence instruments. Also, optical fi lters cures and improved treatment options also detection of weak fl uorescence signals and fi lter sets that offer tunable angles increases, says George. without oversaturation, which is impor- enable spectral adjustment without polar- tant for fl ow cytometry, for instance, says ized light separation—a limitation com- Editor’s note: The “Product Focus” Briggs. Bandpass fi lters that pass only mon in trending microscopy applications. series is intended to provide an over- a narrow band of light are often used; view of the product types discussed. sometimes, longpass or shortpass fi l- Biomedical trends Laser Focus World does not endorse or ters are used to block out the excitation Trends in infrared (IR) and laser recommend any of the products men- wavelength while passing the fl uorescence optics on substrates such as calcium tioned in this article. First published

wavelength. Manufacturing improve- fl uoride (CaF2), barium fl uoride (BaF2), in the January/February 2012 issue of

ments have enabled the production of magnesium fl uoride (MgF2), zinc selenide BioOptics World.

App Makes Android a Power Meter High Power Temperature Controlled Mount Ophir Photonics, global leader in precision laser measurement The Arroyo Instruments’ new equipment 286 High Power TECMount and a Newport provides an excellent Corporation solution for managing your brand, today high heat load applications. announced a The 286 uses a solid Quasar App, copper cold plate and an the fi rst mobile array of high power TECs application that for optimum uniformity, displays laser and offers a 150°C high meter data on temperature option for Android devices. Once connected through Quasar’s Bluetooth, the App elevated testing often displays power readings from the laser measurement sensor within a required in LED applications. range of 10 meters. Internal/external sensor switch for easy connections to DUT temperature sensor. Find out more by visiting our web site. Arroyo Instruments (p) 800-644-0416 www.ophiropt.com/photonics • (p) 866-755-5499 www.arroyoinstruments.com • [email protected]

6 ▲ Summer 2012 Focus On Products www.laserfocusworld.com

FOCUS ON PRODUCTS

ADVERTISER INDEX SUMMER 2012

PAGE ADVERTISER WEB 3 ...... Aerotech, Inc...... www.aerotech.com 6 ...... Arroyo Instruments, LLC ...... www.arroyoinstruments.com 3 ...... Coherent, Inc...... www.coherent.com 1, 7 ...... ConOptics, Inc...... www.conoptics.com 3 ...... Electro-Optics Technology, Inc...... www.eotech.com 3 ...... Exciton, Inc...... www.exciton.com 7 ...... Lambda Research Corporation ...... www.lambdares.com 1, 6 ...... Ophir-Spiricon LLC ...... www.ophiropt.com 8 ...... OptoSigma Corporation ...... www.optosigma.com 8 ...... Sheaumann Laser Inc...... www.sheaumann.com 1, 3 ...... Siskiyou Corporation ...... www.siskiyou.com 1, 8 ...... Terahertz Technologies Inc...... www.terahertztechnologies.com

POSTMASTER: SEND CHANGE OF ADDRESS FORM TO LASER FOCUS WORLD, Omeda Communications, Box 3425, Northbrook, IL 60065–3425. Senior Vice President/Publishing: Christine Shaw Inside Sales Manager: Katrina Frazer; Production Manager: Sheila Ward; Ad Traffi c Manager: Alison Boyer Sales Offi ces: PennWell, Laser Focus World, 98 Spit Brook Road, Nashua, NH 03062-5737, (603) 891-0123 If you wish to reserve space, please contact: Katrina Frazer, Inside Sales Manager, Optoelectronics Group, (p) 603-891-9231, (f) 603-891-0574; [email protected]

Announcing the Release of TracePro 7.2 Pulse Selection System The new TracePro 7.2 software release features a 3D asymmetric CONOPTICS’ PULSE interactive optimizer PICKER allows you to specifi cally designed select from single shot to increase to 30MHz rep rate for productivity by using mode locked lasers a sketch utility to running as high as create CAD geometry, 100MHz. Low Temperal interactive ray tracing Dispersion, compatible for design verifi cation, with fsec pulses, no mouse digitization spatial dispersion. Optical of target functions, transmission > 80%. and an interactive Available for TI: Sapphire optimization process. This new optimizer drastically reduces design and OPO’s 700 to time while giving the user complete control of the optimization process. 1600nm.

ConOptics, Inc. [email protected] 19 Eagle Rd., Danbury, CT 06810 • (p) 800-748-3349 www.lambdares.com/software_products/tracepro/tracepro/ [email protected] • www.conoptics.com

www.laserfocusworld.com Summer 2012 Focus On Products ▲ 7

MedPac, a high power IR source with Optical Laboratory Equipment an aiming beam TTI manufactures a Sheaumann’s MedPac variety of US made is great for medical and products for your optical defense applications. laboratory needs. We It features two diodes, offer O/E converters one consisting of a high in bandwidths from power infrared source of DC to 20 GHz and a 980 or 808nm, and the Phase-Locked-Loop other a red aiming beam. Optical Chopper with The two diodes are direct digital synthesis to individually addressable as well, allowing you to utilize both the aiming provide crystal controlled and high powered beam together or separately. The compact module accuracy and stability with chopping rates from 4 Hz to 5 KHz. Our can reach up to 7W of power out of a 980nm wavelength, 200μm PDA-750 low noise, high gain, Photodiode Amplifi er is designed aperture emitter. They are a fi ber module with an internal thermistor, to provide a direct digital readout of the current generated from a photodiode, and a detachable ST fi ber connector. Please contact us for photodiode, photomultiplier, or other current source. more information on this product. 169 Clear Rd., Oriskany NY 13424 (p) 315-736-3642 • (f) 315-736-4078 [email protected] (p) 508-970-0600 • [email protected] • www.sheaumann.com www.terahertztechnologies.com

Custom OEM Optics and Coatings Low Profi le Motorized Actuator OptoSigma offers a wide selection of optical • Direct replacement for standard micrometer heads (9.5mm or 3/8") components ranging from simple lenses and mirrors to high power laser focusing lenses • 3 micron sensitivity and beamsplitter cubes. We also offer a broad • 13mm travel selection of prisms, windows, fi lters, polarizers and apertures. In addition to standard catalog • Simple DC motor offerings, OptoSigma can supply custom drive with current designs and OEM quantities. limit detection for Thin fi lm coatings can be applied to end of travel catalog, custom or customer supplied optics. • Single handed Refl ective coatings can be applied to uncoated manual operation substrates to make mirrors, beam splitters, polarizers or fi lters. In addition to our wide • Optional RS232C variety of standard coatings, our coating engineers can design a and USB interface custom coating to meet most requirements.

www.optosigma.com www.optosigma.com

Ultralong Working Distance Motorized-Zoom Fiber Laser Focusing Lenses Microscope • Optimized to reduce the effects of thermal expansion at high power • Compact and lightweight levels zoom module • Suitable for solid state • 12 × zoom range lasers such as Yb fi ber laser, YAG laser and YV04 • 500mm WD Low laser magnifi cation model 0.23× - 2.74× • Optimized AR coating from 1040nm - 1150nm • 100mm WD High magnifi cation model 1.25× - 15× • Diffraction limited at f# >2 (NA < 0.25) • Equipped with co-axial epi-illumination port • Manual and Motorized models available

www.optosigma.com www.optosigma.com

8 ▲ Summer 2012 Focus On Products www.laserfocusworld.com