HYDRODYNAMIC EFFICIENCY OF PLANAR TARGETS IRRADIATED BY 351-NM LASER LIGHT (LASER, PLASMA, FUSION, X-RAYS, IONS).

摘要

Measurements have been made of the hydrodynamic efficiency of energy transfer to planar CH targets irradiated by 1 nsec pulses of 351-nm light. This efficiency is measured over a range of intensities varying from 10('13) to 2 x 10('14) W/cm('2) using various targets and irradiation configurations. The energy of the accelerated target is measured using plasma calorimeters on the rear side of the target. Hydrodynamic efficiencies as high as 17% of incident energy are observed. The dependence of this efficiency on intensity, wavelength and target thickness is measured to be: I('0.5), (lamda)('-1.4), and t('-1) respectively. The angular distribution of the blowoff is also reported. This distribution indicates a highly two dimensional behavior in these targets.; The transmitted light and x-ray emission from layered targets were measured in order to determine the depth to which the laser could penetrate. At the highest intensities reported, the laser could penetrate 10 (mu)m of CH at 2 x 10('14) W/cm('2). At this intensity we found indications of significant heating of the rear surface of a 12 (mu)m target as evidenced by the velocity distribution of the accelerated target material. In these distributions the effect of laser transmission is observed; as well as characteristics that indicate preheat in the unablated target mass. The evaluation of the focal intensity distribution provided quantitative measurements of the lack of thermal smoothing in targets irradiated by 351-nm light.; All of the above results were modeled by the two-dimensional hydrocode SAGE('8). These simulations indicated that care must be taken to correctly model the two-dimensional behavior of the targets. For these simulations a flux limiter f = 0.04 was used, though for these intensities the effect of flux limiting is minimal.