Higher order harmonic generation and strong field ionization with Bessel-Gauss beams in a thin jet geometry

TL;DR

This paper demonstrates the use of Bessel-Gauss beams for high-order harmonic generation in a thin gas jet, revealing oscillations in ionization and XUV flux along the propagation axis and highlighting their advantages over Gaussian beams.

Contribution

It introduces a novel application of Bessel-Gauss beams in HHG, showing their ability to produce well-collimated XUV beams and extended phase matching conditions.

Findings

First observation of oscillations in ionization and XUV flux along the propagation axis.

Harmonic yield is not maximized at maximum ionization.

XUV beam remains well collimated despite Bessel beam properties.

Abstract

A promising alternative to Gaussian beams for use in strong field science is Bessel-Gauss (BG or Bessel-like) laser beams as they are easily produced with readily available optics and provide more flexibility of the spot size and working distances. Here we use BG beams produced with a lens-axicon optical system for higher order harmonic generation (HHG) in a thin gas jet. The finite size of the interaction region allows for scans of the HHG yield along the propagation axis. Further, by measuring the ionization yield in unison with the extreme ultraviolet (XUV) we are able to distinguish regions of maximum ionization from regions of optimum XUV generation. This distinction is of great importance for BG fields as the generation of BG beams with axicons often leads to oscillations of the on-axis intensity, which can be exploited for extended phase matching conditions. We observed such oscillations in the ionization and XUV flux along the propagation axis for the first time. As it is the case for Gaussian modes, the harmonic yield is not maximum at the point of highest ionization. Finally, despite Bessel beams having a hole in the center in the far field, the XUV beam is well collimated making BG modes a great alternative when spatial filtering of the fundamental is desired.