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

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 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.

Supercontinuum Induced by Filamentation of Bessel-Gaussian and Laguerre-Gaussian Beams in Water

“…Research Content 0-order BG control of filament [27][28][29][30] accompanied nonlinear phenomena [30][31][32] Higher-order BG control of filament [37] nonlinear propagation and filamentation [38] Higher-order LG multiple filaments [33][34][35][36] Coherence of SC [39] Due to the different geometries (i.e., focal spot shape and size, etc.) of BG and LG beams, the filaments generated by BG and LG beams exhibit different shapes.…”

“…For example, Wang et al tailored the profile of the annular Bessel beams by placing an amplitude mask and iris diaphragm, respectively, before the axicon, and thus the onset and terminal positions of femtosecond laser filament in the fused silica can be arbitrarily controlled [28]. Once the parameters of femtosecond filament are controlled, they are accompanied by several nonlinear phenomena such as photoionization and supercontinuum (SC) generation; fluorescence emission is also affected [30][31][32]. For example, Dota et al studied the filamentation of Bessel beams in BaF 2 by measuring the side emitted fluorescence and transmitted SC [32].…”