Chromatic aberrations correction of attosecond high-order harmonic beams by flat-top spatial shaping of the fundamental beam

TL;DR

This paper demonstrates that flat-top spatial shaping of the fundamental laser beam effectively reduces chromatic aberrations in attosecond high-order harmonic beams, leading to improved control over pulse duration and spectral stability.

Contribution

It introduces a novel method of flat-top beam shaping to mitigate chromatic aberrations in high-order harmonic generation, enhancing attosecond pulse quality.

Findings

Flat-top shaping reduces spectral variation along the beam axis.

Chromatic aberration control improves temporal pulse stability.

Enhanced focus quality of attosecond pulses achieved.

Abstract

Attosecond pulses created by high-order harmonic generation in gases often exhibit strong chromatic aberrations, arising from the broad bandwidth and wavelength-dependent nonlinear light-matter interaction. When the driving laser intensity varies spatially, as for Gaussian driving beams, the apparent source position of the harmonics differs significantly from one order to the next, thus affecting the achievable intensity and duration of the attosecond pulses when they are focused on a target. We show that these chromatic aberrations can be reduced by spatially shaping the fundamental beam to generate high-order harmonics with a driver having a flat-top profile inside the gas medium. By measuring both the intensity profile and wavefront for each harmonic in a plane, we access the extreme ultra-violet (XUV) beam properties and investigate these properties near focus. We observe that controlling chromatic aberrations by flat-top spatial shaping strongly reduces the variation of the XUV spectrum on the beam axis during propagation and, in return, the longitudinal sensitivity of both the temporal profiles and the temporal shifts of the focused attosecond pulses.