Accuracy of the semiclassical picture of photoionization in intense laser fields

TL;DR

This paper critically examines the semiclassical model of photoionization in intense laser fields, revealing discrepancies with quantum calculations and questioning the accuracy of the attoclock technique for measuring ionization times.

Contribution

The study provides a rigorous comparison between semiclassical and quantum calculations, highlighting limitations of the semiclassical model and the attoclock method in accurately determining ionization times.

Findings

Discrepancies between semiclassical and quantum ionization time distributions.

Attoclock technique's inaccuracy in measuring ionization times.

Correlation effects cause deviations from semiclassical predictions.

Abstract

In the semiclassical picture of photoionization process in intense laser fields, the ionization rate solely depends on the amplitude of the electric field and the final photoelectron momentum corresponds to the instant of ionization of the photoelectron, however, this picture has never been checked rigorously. Recently an attosecond angular streaking technique based on this semiclassical perspective has been widely applied to temporal measurement of the atomic and molecular dynamics in intense laser fields. We use a Wigner-distribution-like function to calculate the time-emission angle distribution, angular distribution and ionization time distribution for atomic ionization process in elliptically polarized few-cycle laser fields. By comparing with semiclassical calculations, we find that the two methods always show discrepancies except in some specific cases and the offset angles are generally not consistent with the offset times of the ionization time distributions obtained by the two methods even when the non-adiabatic effect is taken into account, indicating that the "attoclock" technique is in principle inaccurate. Moreover, calculations for linearly polarized laser fields also show similar discrepancies between two methods in the ionization time distribution. Our analysis indicates that the discrepancy between the semiclassical and quantum calculations can be attributed to correlation, i. e., temporal nonlocalization effect.