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Laser-matter interactions at sub-micron laser wavelengths Pasini, Daniel


In recent years there has been considerable interest in the use of sub-micron wavelength lasers for target irradiation in laser fusion experiments. We present here an experimental investigation of laser-matter interaction in this short wavelength regime. We have irradiated planar targets with 0.532, 0.355 and 0.266 μm laser light with pulse lengths of 2 ns and at intensities ranging from 10¹² to 5 X 10¹³ W/cm². The results show that for these conditions inverse bremsstrahlung is very effective and leads to very high absorption (~ 95%). The X-ray spectrum also show that the absorbed energy is well thermalized and only a small number of energetic, non-thermal electrons are present. Also a very low level of scattered light was measured indicating that laser-plasma collective processes are not important. Energy transport was investigated using multilayer targets. Anomalous laser penetration depths in the target were obtained in these measurements. This has been successfully explained in a simple hydrodynamic model where two-dimensional effects were taken into account. In the study of the ablation process wavelength and intensity scaling laws for the mass ablation rate and ablation pressure have been obtained. These results show the inadequacy of the present analytical theories of the laser-driven ablation process.

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