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.
Highlights
Studying trajectory resolved contributions to the high-order harmonic generation (HHG) spectrum is an attractive proposition because different trajectories probe very different ionization conditions and have different excursion times
In this paper we report on measurements made with very well-controlled, high repetition-rate laser pulses, which allow us to make trajectory resolved HHG measurements in argon gas while varying the ellipticity and the peak field strength of the driving laser pulses
The results allow us to elucidate new features in the sub-cycle ionization step that lead to long trajectories, that is, ionization at high field strengths followed by long excursion times
Summary
The experimental setup used for the experiment presented in this article is described in a recent publication[28] and is briefly outlined here. The laser system has a variable repetition rate between 1 and 600 kHz, but all the presented data were recorded at a repetition rate of 20 kHz. The pulses were focused tightly into a continuous argon gas jet, with a 90 m orifice, using a 100 mm focal length achromatic lens. After the interaction region, a differential pumping hole with an inner diameter of 0.5 mm was placed to minimize the background gas in the detection chamber. The differential pump hole allowed for a pressure difference of the background gas between the generation and detection chambers of 4–5 orders of magnitude. The grating diffracts and refocuses the XUV in the horizontal direction while the vertical direction is left unaffected. The vertical direction provides the divergence of the XUV light while the horizontal direction shows the spectrum
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
