PRODUCTION OF VERY LARGE, SUB-10TH-CRITICAL PLASMAS FOR LASER-FUSION RESEARCH

The development of a plasma environment that is appropriate for the study of low-gain processes in laser-fusion plasma is reported. These plasmas have long scale lengths, low densities, and no quarter-critical or critical-density surfaces. The plasmas were created by two-sided irradiation of CH foils with 15 kJ of 351 nm laser light. When the peak electron density in the plasma had decayed to about 2 x 10(20) cm-3, the parabolic density profile was estimated to have a full width at half-maximum of 3 mm and the electron temperature was estimated to be 1 keV. Probe lasers of different wavelengths were used to measure the peak electron density via stimulated scattering processes and odd half-harmonic generation. Sufficiently accurate modeling of the laser-irradiation conditions led to improved agreement between the experiment and two-dimensional (2-D) computer simulations.