Electron temperature of optically ionized gases produced by high intensity 268 nm laser radiation

Abstract

Thomson scattering measurements have been used to determine the electron energy distribution in UV optically ionized He and Ne at pressures up to 1/2 bar irradiated at 3×${10}^{17}$ W/${\mathrm{cm}}^2$ in 12 ps. The electrons evolve from a multiphoton ionization spectrum to a thermal distribution with increasing pressure. The low frequency part of the scattered spectrum clearly shows the ‘‘zero-damped’’ ion acoustic mode for high values of ${\mathit{ZT}}_{\mathit{e}}$/${\mathit{T}}_{\mathit{i}}$. Experimental and modeling results indicate that nonlinear inverse bremsstrahlung heating and radial conduction cooling dominate the electron energy balance.