Abstract: The efficiency of laser light energy absorbed by the coronal plasma of target is crucial to laser fusion. Using prepulse to irradiate target for increasing absorption efficiency of high intensity incident laser beam is considered and some theoretical simulations have been done. 1-D non-LTE radiative hydrodynamic code is used to simulate the interactions of laser beam with matter. The basic equations of this code are consisted of:the 1-D equations of radiative hydrodynamics, the average-atom population rate equations, the multigroup flux-limited diffusion equations for radiation transport, and the equations for deposition of laser light energy in plasma. The following physical processes are considered:the bremsstrahlung effect, radiative ionizations and recombinations, collisional ionizations by electrons and three-boby recombinations, collisional excitations and de-excitations by electrons, radiative line transitions and Compton scattering.A gaussian laser prepulse of wavelength 1.06μm, FWHM 600ps and peak intensity 1.5×10¹²W/cm² was used to irradiate thickness 20μm Au plate target, after 3ns a main gaussian pulsewith wavelength 1.06μm, FWHM 600ps and peak intensity 3.0×10¹⁴W/cm² irradiated the expanding Au plasma. The responces of laser-produced plasma conditions are shown. By comparison with without prepulsing, under the condition of same main incident laser pulse, the absorption efficiency is increased from 0.36 to 0.60 and the laser-x-ray conversion efficiency is increased from 0.16 to 0.25. The electron temperature of hot plasma is also higher than without prepulsing, and the x-ray spectrum which is emitted from laser-produced hot plasma is harder and more intense than without prepulsing. The responces of laser-produced plasma for Fe target with prepulsing are shown as well. The conclusion is that using prepulsing is useful way for getting high absorption laser beam.

Key words: prepulsing laser beam, absorption, laser-x-ray conversion efficiency