The new results obtained in experiments on the "Mishen" facility with laser-irradiated low-density porous media are presented and discussed. The variety of optical and X-ray diagnostic methods was used to characterize physical processes in laser-irradiated (λ = 1.054 μm, τ = 3 ns, I = 1013 - 1014 W/cm2) plane porous samples of different microstructure and chemical composition; an average density was varied in the range from 1 mg/cm3 to 20 mg/cm3. The features of laser light absorption and scattering as well as the efficiency of energy transport through porous layer to solid-density foil installed at the target rear-side were studied in dependence on the incidence angle of laser beam, average density, thickness and structure of irradiated porous layer. The plasma formation and energy transport processes are found to differ significantly in laser-irradiated low-density matter of different microstructure (chaotic fibrous structure agar, quasi-regular cellular polystyrene foam). The expansion of high-Z plasma was studied in experiments with porous layers deposited on the surface of plane high-Z targets. Desirable suppression of X-ray emitting plasma motion by porous material was obtained.
To experimentally model laser-plasma interaction in low-density porous media, we have started irradiating plastic multifoil targets with a single 1.054 μm laser beam at approximately 1014 W/cm2 at the "Mishen" facility. A first foil directly irradiated was thin enough to burn through and rapidly become underdense. Acceleration and expansion of the high-temperature plasma inward the target, its stagnation under impacts on successive foils, and reverse shock propagation into the plasma corona occur during the laser pulse. Hydrodynamics of plasma in multifoil targets was studied by analyzing the spectral shifts of backscattered laser light and its harmonics. The experimental data interpretation employs results of the one-dimensional hydrodynamic simulation.