ELECTRON-TEMPERATURE OF OPTICALLY IONIZED-GASES PRODUCED BY HIGH-INTENSITY 268 NM LASER-RADIATION

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 x 10(17) W/cm2 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 ZT(e)/T(i). Experimental and modeling results indicate that nonlinear inverse bremsstrahlung heating and radial conduction cooling dominate the electron energy balance.