Maximizing the brilliance of high-order harmonics in a gas jet

We have measured the wave front of high-order harmonics generated in a gas jet with a Hartmann sensor. With this setup we have investigated the influence of typical adjustable parameters such as gas pressure and focal position as well as the spatial laser beam profile on the conversion efficiency and the extreme ultraviolet (XUV) beam profile. Independent of the control parameter we always observed the highest conversion efficiency in connection with the best beam profile, i.e. the highest flux corresponds also to the highest brilliance. Furthermore, we have shown that aberrations of the fundamental laser beam are not simply imprinted onto the XUV beam.