Plasma experiments with 1.06 μm lasers at the Lawrence Livermore Laboratory

Irradiation experiments were performed with the two beam Nd:YAG glass laser systems, Janus(approximately less than 40 J/100 psec, approximately 0.4 TW), Cyclops (approximately less than 70 J/100 psec, approximately 0.7 TW), and Argus (approximately less than 70 J, 35 psec, approximately 2 TW). Two classes of targets have been used, glass microshells (approximately 40 to 120 μm diameter x approximately 0.75 μm wall thickness) filled with an equimolar DT mixture and disks (approximately 160 to 600 μm diameter x approximately 10 μm thick) of several compositions. The targets were supported in vacuum (pressure approximately less than 10-5 Torr) by thin glass stalks. This paper reports results related to the propagation, absorption and scattering of laser light by both spherical and planar targets. The absorption measurements cannot be explained using only inverse Bremsstrahlung. The scattered light and the plasma energy are polarization dependent, which is evidence of resonance absorption. The x-ray spectra are characterized by a thermal and a suprathermal distribution. The ''temperature'' of the hot x-rays is given by theta/sub H/ approximately equals I.3-.4 depending on the target material. Evidence is also presented which indicates that the laser radiation pressure is producing density steepening in the region of the critical density with n/sub cr/(delta n/delta x)-1/sub cr/ approximately sigma(1 μm) and in some cases plasma filamentation is observed