Propagation effects in optical-field-induced gas mixture breakdown for recombination x-ray lasers

A two-dimensional pulse propagation model which solves the paraxial wave equation in cylindrical geometry, is used to study argon doped with hydrogen targets. The code includes optical-field ionization, refraction and diffraction effects, above-threshold ionization and inverse bremsstrahlung electron heating mechanisms. A range of target and pump laser parameters are examined and a 4 mm long, 12 mu m wide channel may be formed which is suitable for x-ray lasing. A one-dimensional Lagrangian hydrodynamics model is subsequently used as a postprocessor to simulate the recombination phase with both the plasma effects and atomic kinetics included. Calculated gain coefficients above 300 cm(-1) at 232 Angstrom in Na-like Ar are found throughout the channel but with a saturation intensity of the order of 10(7) W cm(-2).