ENERGY-TRANSPORT IN PLASMAS PRODUCED BY A HIGH-BRIGHTNESS KRYPTON FLUORIDE LASER FOCUSED TO A LINE

A high brightness krypton fluoride Raman laser (wavelength 0.268 mum) generating 0.3 TW, 12 ps pulses with 20 murad beam divergence and a pr epulse of less than 10(-10) has been focused to produce a 10 mum wide line focus (irradiances approximately 0.8-4 X 10(15) W cm-2) on plasti c targets with a diagnostic sodium fluoride (NaF) layer buried within the target. Axial and lateral transport of energy has been measured by analysis of x-ray images of the line focus and from x-ray spectra emi tted by the layer of NaF with varying overlay thicknesses. It is shown that the ratio of the distance between the critical density surface a nd the ablation surface to the laser focal width controls lateral tran sport in a similar manner as for previous spot focus experiments. The measured axial energy transport is compared to MEDUSA [J. P. Christian sen, D. E. T. F. Ashby, and K. V. Roberts, Comput. Phys. Commun. 7, 27 1 (1974)] one-dimensional hydrodynamic code simulations with an averag e atom post-processor for predicting spectral line intensities. An ene rgy absorption of approximately 10% in the code gives agreement with t he experimental axial penetration. Various measured line ratios of hyd rogen- and helium-like Na and F are investigated as temperature diagno stics in the NaF layer using the RATION [R. W. Lee, B. L. Whitten, and R. E. Strout, J. Quant. Spectrosc. Radiat. Transfer 32, 91 (1984)] co de.