Characterization of a cluster jet for quasi-phase matching of high harmonic generation

We investigate the possibility to realize a fully coherent light source emitting XUV down to a wavelength of 4 nm by using high harmonic generation (HHG). The source will be based on ions rather than on neutral atoms as used in a standard approach. Due to ionization of the generating plasma medium, current phase-matching techniques applied to HHG in neutral gases are not suitable. Instead, we will investigate quasi-phase matching (QPM) and wave guiding over an extended interaction length to increase the output pulse energy. For this, we will ionize a density modulated cluster jet to prepare a plasma waveguide for the drive laser with an appropriate density modulation along its axis for QPM.Here we report on the initial characterization of the argon cluster jet that at a later stage will be modulated. We employ Rayleigh scattering imaging combined with interferometry to infer the cluster size, and the cluster and gas density distribution in the jet. The results will be compared to calculations with a quasi-one-dimensional fluid dynamics model.