Study of thermal smoothing by shock speed measurement

Summary form only given. Intensity nonuniformities in an incident laser beam may cause corresponding variations in the ablation pressure. The variations in the ablation pressure should be less than a few percent in order for spherical targets to implode symmetrically and to be ignited in inertial confinement-fusion experiments. The uniformity requirements on the laser beam could be eased by the degree of lateral heat conduction and plasma-hydrodynamic motions occurring between the absorption and the ablation surfaces. Theoretically, the scaling of the smoothing on the standoff distance (D) between the absorption and the ablation surfaces and the intensity-modulation wavelength (L) is obtained in terms of heat conduction and plasma-fluid motions. Experiments were conducted with a 0.53-/spl mu/m, 1-ns (FWHM), Gaussian shaped laser beam focused onto thin polystyrene targets. The smoothing factor shows a clear exponential decrease as D/L increases.