强激光束与空腔靶相互作用实验研究

1.06μm波长的强激光束辐照Au材料制作的空腔靶,采用目前国内最先进的诊断设备。对腔内高温等离子体现象演变规律进行了实验观察,获得了反射激光、能量吸收、X光转换、亚千X光能谱及时空特性、辐射温度、超热电子等重要物理信息,并就实验结果作了必要的分析和讨论

EXPERIMENTAL INVETIGATIONS OF PROPERTIES OF PLASMA GENERATED BY INTENSE LASER BEAM IN HOHLRAUM TARGETS

In order to study the behaviour of plasma generated by laser beam in hohl-raum targets. we have performed a series of experiments in the Past three years, The experiments were conducted on a Nd: glass laser facility. The laser pulse parameters were as follows: wave length 1.06um. energy of laser pulse 150J-450J. pulse duration 0.7-1 ns. ratio of signal to noise 105 -106. energy of amplified stimulated spontaneous emission< 0.8mJ. beam angle drift<5", beam angle divergency<0. 1m rad and wavefront radius 300m.escaping from the diagnostic hole and it's angular distribution, spatial distribution of x-ray emission intensity in partial plasma area and x-ray line spectrum.The time-resolved intensities of the laser light scattered from cavities of hohlraum targets are higher than those from surfaces of planar targets and the former have peaks more than one.The energy absorption efficiencies of hohlraum targets are about 70%. much higher than those of planer targets.The energy spectrum of subkilovolt x rays escaping from the diagnostic hole of the hohlraum targets closely follows a Planck's distribution. The temperature calcuated from this distribution is about 120eV.The temporal intensity distributions of x rays escaping from the diagnostic hole have a long tail. The time duration of x rays emitted by hohlraum targets is 3-5 times longer than that by planar targets.The energy of suprathermal x rays emitted by hohlraum targets is one erder of magnitude more than that emitted by planar targets. The suprathermal electron temperature is about 50keV.The experiments show clearly that hohlraum targets have higher laser energy absorption efficiencies. As high temperature plasma in the cavity can be confined for a longer time period, the conversion efficiencies from laser energy to x-ray radiation are also higher. All of these are of great importance to radiation transport and opacity researches. However suprathermal electrons and their high temperatures in the hohlraum targets mean that we must improve our target configurations and develop frequency conversion technique .