HEATING OF UNDERDENSE PLASMAS BY INTENSE SHORT-PULSE LASERS

A one-dimensional model in cylindrical geometry which incorporates tunnel ionization, nonlinear inverse bremsstrahlung, and radial heat conduction is used to predict the spatial and temporal temperature distribution in an undercritical plasma irradiated axially by a short-pulse laser. Results from the calculation are compared to available experimental data using a 12 ps KrF laser and to previous work in a regime relevant to proposed recombination optical-field ionized xuv lasers in the transient regime, e.g., Li-like neon. The calculated temperature is too high for lasing to the ground state because of the large contribution from inverse bremsstrahlung for pulse lengths greater than 100 fs. It is shown that for small filaments, additional cooling by supersonic heat conduction on a few picosecond time scale could be used efficiently to generate inversion between excited states in the quasi-steady-state regime. © 1994 The American Physical Society.