Self-Consistent Electron Density Profiles in Short Pulse, 1.054 µm Laser-Heated Plasmas

Abstract

A one-dimensional Eulerian fluid code has been used to calculate the influence of radiation pressure for the case of a short (picosecond) neodymium laser pulse obliquely incident onto a planar target. The code self-consistently solves the fluid equations and Maxwell’s equations on the time-dependent density profile of the expanding plasma. At each time step the value of the ponderomotive force is calculated from the electromagnetic field quantities and added to the thermal pressure term in the momentum equation. The damping of the resonant electric field due to plasma wave convection in the case of p-polarized laser light is expressed in terms of an effective collision frequency ν eff = ω(λ D/L)2/3, with L being the self-consistently steepened density scale length near critical density. In this way time-dependent density profiles have been obtained for p- and s-polarized irradiation at an angle of 20° for a range of incident laser intensities between 1011 and 1015 W/cm2. Profile steepening is found to be effective even at intensities as low as 1013 W/cm2 in the case of p-polarized irradiation, whereas for s-polarization intensities well above 1014 W/cm2 are required for significant profile steepening at critical density.