Science on the attosecond scale
Lawrence Berkeley Lab - 16 April 2010
Time-resolved spectroscopy of attosecond quantum dynamicsTime on the scale of electrons
Among the most urgent challenges facing our nation are ways to use present energy sources far more efficiently while creating the carbon-free sources of the future. Artificial photosynthesis means mimicking the way nature does it, moving electrons through hundreds of superfast chemical steps; conserving electricity during transmission means building tough, flexible high-temperature superconductors; better solar cells depend on better ways for semiconductors to turn light energy into flowing electrons.
These and numerous other advances in energy, green chemistry, and human health must start with understanding the movement of electrons – making frame-by-frame movies of changing molecular bonds during chemical reactions, or the correlated behavior of electrons in complex solids. This will only be possible by freezing time within a few quintillionths of a second.
How is it possible to create pulses of light so short? Steve Leone, a pioneer in the field of ultrafast lasers, tells how it’s done.
- Chemical Physics Letters, Volume 463, Issues 1-3, 22 September 2008, doi: 10.1016/j.cplett.2008.08.059
Isolated attosecond pulses from ionization gating of high-harmonic emissionThe advent of attosecond pulsed radiation leads to a large unexplored scientific area in chemical physics: the direct time-resolved measurement of electronic quantum dynamics. Major scientific goals include spectroscopy of single- and multi-electron motion and dynamical electron correlations, relating to orbital interactions in valence and core electronic levels of atoms and molecules. The results of such studies address a wide array of scientific and technological applications. Here, the current state-of-the-art of attosecond-dynamics measurements is reviewed and several novel spectroscopic methods are discussed that are particularly important for applications in chemical physics: attosecond transient absorption/dispersion spectroscopy, laser-induced-dipole spectroscopy, and absolute-phase spectroscopy.
- Chemical Physics, Volume 366, Issues 1-3, 10 December 2009, doi: 10.1016/j.chemphys.2009.09.016
Combining results from several techniques of attosecond spectroscopy, we show that ionization gating of high-harmonic emission on the leading edge of the driving pulse produces isolated attosecond pulses with a contrast ratio (the energy in the main pulse normalized to the energy in adjacent satellite pulses) c=3.3±0.2. Half-cycle cutoff analysis confirms that harmonic generation proceeds in the ionization-gated regime. The attosecond pulse contrast is measured using the technique of carrier–envelope phase (CEP)-scanning, recently developed by our group, in which photoelectrons generated from Ne atoms by the harmonic pulse are streaked as a function of CEP. Streaking of photoelectrons as a function of attosecond time delay also confirms the isolated nature of the harmonic pulse, which is measured to have a duration of 430±15 as, limited by the bandwidth of the reflective X-ray optics employed. The combined measurements imply that the experimental advantages of the ionization gating technique—tunable X-ray emission, relaxed sensitivity to the CEP and scalability to longer driver pulses—are also conferred on isolated attosecond pulse production.