CHARACTERIZATION OF LASER PLASMAS FOR INTERACTION STUDIES

Long scale length plasmas were produced by uniform laser irradiation f rom opposite sides of metal disks coated on thin plastic stripe target s. The plasma became fully underdense before the end of the 600-ps pul se. The evolution of the plasma was carefully characterized both in el ectron density and temperature, and the experimental data were compare d to the predictions of a one-dimensional hydrodynamics computer code. The electron temperature was obtained from time-resolved x-ray spectr a by line-ratio measurements, accounting for opacity effects. Two-dime nsional electron density profiles of a large plasma region were obtain ed by Nomarski interferometry at different times. They showed that the expansion was axially symmetric and reproducible shot by shot. The pl asma was found to be substantially free from small-scale density inhom ogeneities. The plasma produced with this techique is very suitable fo r interaction experiments. In particular, laser stimulated plasma inst abilities of relevance for laser fusion can be accurately studied in t hese conditions.