Characterization of laser plasmas for interaction studies

Long scale length plasmas were produced by uniform laser irradiation from opposite sides of metal disks coated on thin plastic stripe targets. The plasma became fully underdense before the end of the 600-ps pulse. The evolution of the plasma was carefully characterized both in electron density and temperature, and the experimental data were compared to the predictions of a one-dimensional hydrodynamics computer code. The electron temperature was obtained from time-resolved x-ray spectra by line-ratio measurements, accounting for opacity effects. Two-dimensional electron density profiles of a large plasma region were obtained by Nomarski interferometry at different times. They showed that the expansion was axially symmetric and reproducible shot by shot. The plasma was found to be substantially free from small-scale density inhomogeneities. The plasma produced with this techique is very suitable for interaction experiments. In particular, laser stimulated plasma instabilities of relevance for laser fusion can be accurately studied in these conditions. © 1994 The American Physical Society.