Characterization of germanium stripe x-ray lasers

One method of improving the transverse spatial coherence of x-ray lasers (XRLs) is by adaptive spatial filtering of XRL apertures using geometric shaping in the form of bowtie or wedge XRLs. However, we must maintain the desired geometric shapes in exploding foil or slab configurations during the lasing period. As a first step toward understanding lasing in such geometries, we study the behavior of simple stripe XRLs. Past experience with stripe XRLs deposited on thick plastic substrates resulted in significantly weaker laser intensities as compared to line-focused slab XRLs. Possible reasons for this intensity reduction of stripe XRLs could include mixing at the laser boundary, and changes in plasma, kinetics, and hydrodynamic properties that affect laser gains and propagation. We present experimental and theoretical characterizations of germanium line-focused slab and stripe XRLs. Key experimental parameters we are studying include images of emission profiles of the laser blowoff, angular divergences, XRL output intensities, and ionization balances as we vary XRL designs. We compare the experimental results with 2D laser deposition and hydrodynamics simulations using LASNEX, and study the changes in ionization balances and level populations from postprocessing LASNEX results.