Progress in FWSD non-linear effects with XRLs

Progress of a four-wave sum difference frequency generation scheme to convert coherent soft X-ray radiation to shorter wavelengths, using a plasma medium is discussed. Results are presented from a preliminary experiment, involving the Ne-like Ni XRL (λ XRL = 0.023 μm) mixed in phase-matched mode with a Nd:glass laser (λ OPT = 1.054 μm) in a Na-like Argon plasma. A 25 mm single slab target of Ni pumped with ∼ 200 J of energy from 5 optical beams has routinely produced ∼ 3 mJ of XRL energy at 23.1 nm. The XRL was split and recombined and information from fringe visibility measurements has been used to estimate the degree of spatial coherence in the XRL. Characterisation of the gas jet mixing medium has been carried out through emission spectroscopy and optical interferometry.