Spectroscopic measurements of ion acoustic decay instabilities in laser produced plasma

Abstract

Summary form only given. Extensive studies of spectroscopic measurements of IADI (ion-acoustic decay instability) in laser-produced plasma have been made. The experiments were performed using the GDL (gas dynamic laser) laser facility at LLE and the Janus (Phoenix) laser and NOVA laser facilities at LLNL. The laser is incident normally onto a planar target (CH, Al, Cu, Mo and Au of 50-mm thickness) with a 1-ns FWHM Gaussian pulse and a maximum energy of 200 J. The IADI was studied by monitoring the Stokes sideband of the backscattered (0 and 45d) spectrum near the second harmonic of the laser light. Two spectrometers were used to measure the angular dependence of the time integrated 2o signal. Extensive studies of IADI have been made: (1) measurements of the threshold vs. laser spot size, (2) laser wavelength scaling (1-mm and 0.5-mm laser irradiations), (3) plasma flow effect, measurements of the angular dependence of 2o signal, (4) measurements of IADI in high-Z target, ionic charge state Z, and IADI vs. target material, and (5) the measurements of IADI in the high-laser-intensity regime. The thresholds of the IADI are quite low, even with the high-Z target, so that IADI is potentially important in laser-produced plasma