Sub-cycle ionization dynamics revealed by trajectory resolved, elliptically-driven high-order harmonic generation

TL;DR

This paper reveals sub-cycle electron ionization dynamics in high-order harmonic generation driven by elliptically polarized lasers, highlighting trajectory differences, ellipticity effects, and resonance shifts crucial for attosecond science.

Contribution

It introduces a trajectory-resolved analysis of high-order harmonic generation under elliptical polarization, emphasizing the importance of sub-cycle electron velocity changes and dynamic Stark shifts.

Findings

Different electron trajectories have distinct sensitivities to ellipticity.

Resonant enhancement depends on dynamic Stark shifts shifting resonances.

Accurate modeling requires including sub-cycle velocity and excursion time changes.

Abstract

The sub-cycle dynamics of electrons driven by strong laser fields is central to the emerging field of attosecond science. We demonstrate how the dynamics can be probed through high-order harmonic generation, where different trajectories leading to the same harmonic order are initiated at different times, thereby probing different field strengths. We find large differences between the trajectories with respect to both their sensitivity to driving field ellipticity and resonant enhancement. To accurately describe the ellipticity dependence of the long trajectory harmonics we must include a sub-cycle change of the initial velocity distribution of the electron and its excursion time. The resonant enhancement is observed only for the long trajectory contribution of a particular harmonic when a window resonance in argon, which is off-resonant in the field-free case, is shifted into resonance due to a large dynamic Stark shift.