Into the Attoworld

Home , Attosecond, Attosecond physics, Femtosecond

Milestones

Theoretical and experimental become available, such information MILESTONE 22 groundwork — notably by Anne could be obtained with ångström L’Huillier and colleagues — showed spatial resolution and attosecond that driving high-harmonic genera- temporal resolution. Into the attoworld tion with a multi-cycle femtosecond We are only 10 years into the new laser should produce attosecond light millennium, but attosecond technol- pulses, which are repeated at twice ogy has already established itself. The the laser frequency. Rigorous proof hope now is that by moving from the 1.0 of attosecond pulse trains arrived mere shaping to the complete engi- only in 2001, however, when Pierre neering of light waves — composed Agostini and colleagues encoded the of frequencies from the UV to the 0.5 properties of the pulses in photo- infrared — unprecedented control

d ionized electrons and then measured over electron motion will become the characteristics of these so-called feasible. This promises access to 0.0 photoelectron replicas. attosecond pulses of coherent hard

Electric fiel A few months later, Ferenc Krausz X-rays that would revolutionize X-ray and colleagues reported the first laser research. Ultimately, light-wave –0.5 individual attosecond pulses, filtered engeneering should also give access out of pulse trains. The team then per- to pulses rivalling the atomic unit of fected the art of steering re-collision time (~24 as) in duration that would –1.0 –3 0 3 electrons, using the electric fields of allow us to capture — and even con- Time (femtoseconds, 10–15 s) intense few-cycle laser pulses, with trol — the fastest motions outside the their waveform judiciously adjusted atomic core. (Milestone 16) so that each pulse Magdalena Helmer, Senior Editor, Nature The initial femtosecond pulse used to ionize atoms is The new millennium has heralded generates only one reproducible re- shown in red, and the train of the arrival of attosecond light pulses, collision event and, hence, one repro- ORIGINAL RESEARCH PAPERS Schafer, K. J., attosecond pulses of and with it the emergence of a radi- ducible isolated attosecond pulse. Yang, B., DiMauro, L. F. & Kulander, K. C. Above higher-frequency light that it threshold ionization beyond the high harmonic produces is shown in blue. cal new technology that is moving Atomic Auger decay and the photo- cutoff. Phys. Rev. Lett. 70, 1599–1602 (1993) | The offset between the peak time-resolved spectroscopy and ionization of atoms and solids have all Corkum, P. B. A plasma perspective on strong of the initial pulse and the field ionization. Phys. Rev. Lett. 71, 1994–1997 peak of the attosecond pulse control techniques from the molecu- been triggered by such isolated atto- (1993) | Antoine, P., L’Huillier, A. & Lewenstein, M. corresponds to the length of lar (femtosecond) to the electronic second photon pulses, and the ensuing Attosecond pulse trains using high-order time the liberated electron is (attosecond) timescale. electron dynamics has been probed by harmonics. Phys. Rev. Lett. 77, 1234–1237 (1996) | catching a ride in the Paul, P. M. et al. Observation of a train of oscillating electric field of the In fact, attosecond light pulses the synchronized oscillating electric attosecond pulses from high harmonic femtosecond pulse, which generation. Science 292, 1689–1692 (2001) | moves it away from and then were created in the early 1990s, when field of the laser pulse that generated back to its parent ion. Hentschel, M. et al. Attosecond metrology. physicists ionized rare-gas atoms the attosecond trigger. Nature 414, 509–513 (2001) | Drescher, M. et al. with intense laser pulses to gener- The ionization process at the heart Time-resolved atomic inner-shell spectroscopy. ate energetic radiation alongside of high-harmonic generation itself Nature 419, 803–807 (2002) | Baltuska, A. et al. Attosecond control of electronic processes by the original optical pulse. Theory launches electronic and structural intense light fields. Nature 421, 611–615 (2003) | exploring such ‘high-harmonic changes, with the emitted attosecond Niikura, H. et al. Probing molecular dynamics with generation’, from Kenneth Kulander electron and photon pulses provid- attosecond resolution using correlated wavepacket pairs. Nature 421, 826–829 (2003) | and co-workers and from Paul ing a snapshot of the structure and Baker, S. et al. Probing proton dynamics in Corkum, resulted in 1993 in a simple dynamics of the system at the time molecules on an attosecond timescale. Science 312, 424–427 (2006) | Uiberacker, M. et al. model for the process: during each of the re-collision. This structural Attosecond real-time observation of electron half-cycle, the oscillating electric and dynamic information can be tunnelling in atoms. Nature 446, 627–632 (2007) | field of an intense laser pulse will retrieved: imaging of molecular Cavalieri, A. L. et al. Attosecond spectroscopy in condensed matter. Nature 449, 1029–1032 (2007) | tear electrons from atoms in a gas, structure through re-collision elec- Meckel, M. et al. Laser-induced electron tunneling accelerate them away and then drive tron diffraction, and the measure- and diffraction. Science 320, 1478–1482 (2008) them back to re-collide with their ment of attosecond proton dynamics FURTHER READING Agostini, P. & DiMauro, L. F. The physics of attosecond light pulses. Rep. Prog. parent ion. In each collision, a short and multi-electron dynamics in mol- Phys. 67, 813–855 (2004) | Krausz, F. & Ivanov, M. burst of extreme ultraviolet (XUV) ecules have all been reported. When Attosecond physics. Rev. Mod. Phys. 81, 163–234 photons is created. more intense attosecond pulses (2009)