Nonuniform laser ablation caused by nonuniform laser irradiation and initial target roughness induces ripples of shock and ablation surfaces in laser implosion. Hydrodynamic perturbation growth before the shock breakout is investigated by using an analytical model and two-dimensional simulations. The model agrees well with simulation and experimental results. Areal mass density perturbations and growth rate of the Richtmyer-Meshkov instability are estimated for an ignition target. The thermal smoothing in the ablation layer is also studied for perturbations with a wavelength longer than the layer thickness. A large increase of temperature and density perturbations is shown instead of the smoothing for such a wavelength. (C) 1998 American Institute of Physics. [References: 18]
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