  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.
