Investigation of density depression in a laser-created plasma

Summary form only given, as follows. Tabletop X-ray lasers have been used in applications to diagnose high-density plasmas using their coherent properties. Recently, these lasers have demonstrated their usefulness by providing interferometry data on laser-produced plasmas reaching to near critical densities. Several initial experiments have obtained valuable and surprising results. Obtained density profiles show the generation of a density depression along the laser focus. Though axial jets and filaments in plasma were reported earlier in numerous experimental works, the formation of inhomogeneities in the density profile of such large magnitude at such relatively small laser fluxes has never been seen before. Density profiles reaching near-critical for a plasma heated by small-energy Nd-glass lasers, show both plasma blow-off from an increased effective spot and the creation of side lobes. This description seems in contradiction with the classical description of steady-state spherical plasma expansion under the influence of laser radiation. We used available numerical codes LASNEX and RADEX to evaluate the obtained plasma parameters and present our results.