Theoretical Analysis and Numerical Simulation of Attosecond Time Delays in Photoionization

<p>Recent developments in laser technology, in particular the advances in high-harmonic generation,\&nbsp;<span style="line-height: 1.6em;">enable the generation of ultrashort extreme ultraviolet (XUV) pulses with attosecond (1\&nbsp;</span><span style="line-height: 1.6em;">as = 10<sup>-18</sup> s) duration. Such tools open the opportunity to study electron dynamics in atoms\&nbsp;</span><span style="line-height: 1.6em;">and molecules on its intrinsic time scale. As an example, the attosecond streaking technique was\&nbsp;</span><span style="line-height: 1.6em;">recently applied to time resolve the photoionization process in atomic and solid systems. In this\&nbsp;</span><span style="line-height: 1.6em;">technique, an isolated attosecond XUV pulse that ionizes the electron in the target system, is superimposed\&nbsp;</span><span style="line-height: 1.6em;">with a few-cycle streaking pulse (usually of near-infrared wavelengths). The streaking\&nbsp;</span><span style="line-height: 1.6em;">pulse modulates the final momentum (or energy) of the photoelectron. The measured streaking\&nbsp;</span><span style="line-height: 1.6em;">trace, i.e., the final momentum (or energy) as a function of the relative delay between these two\&nbsp;</span><span style="line-height: 1.6em;">pulses, contains time information of the photoionization process. By comparing two streaking\&nbsp;</span><span style="line-height: 1.6em;">traces measured for photoionization from the 2s and 2p orbitals in a neon atom, Schultze et al.\&nbsp;</span><span style="line-height: 1.6em;">[Science 328, 1658 (2010)] found a temporal offset of 21 \textpm 5 as between them and interpreted this\&nbsp;</span><span style="line-height: 1.6em;">value as the time delay between photoionization from the 2s and 2p orbitals. This experiment has\&nbsp;</span><span style="line-height: 1.6em;">initiated a debate among theoreticians, in particular about the origin of the measured time delay. A\&nbsp;</span><span style="line-height: 1.6em;">correct interpretation of the delay is extremely important for our understanding of the attosecond\&nbsp;</span><span style="line-height: 1.6em;">streaking technique and an exact analysis of time resolved measurements of this and other ultrafast\&nbsp;</span><span style="line-height: 1.6em;">processes.</span></p>
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University of Colorado Boulder
Boulder, CO
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