INVESTIGATION OF SHOCK WAVE LOADING AND CRATER CREATION BY MEANS OF SINGLE AND DOUBLE TARGETS IN THE PALS-LASER EXPERIMENT

摘要

The efficiency of crater creation for different types of Al targets, namely, single massive targets and double targets consisting of a foil or a disk placed before the massive target at a chosen distance (300 and 500 μm), is studied. Targets were irradiated by the PALS facility laser beam with E_l = 100-400 J at the first harmonic λ = 1315 nm, a focal spot radius of 125 μm, and pulse duration of 400 ps. Velocities of the accelerated foil's fragments or disks and electron density distributions of the plasma streams are determined by means of three-frame interferometry. Shapes and volumes of craters are obtained using the crater replica technology and microscopy measurements. It is shown that direct laser action is the most efficient way of energy transfer to the massive target and the most efficient method of crater creation. Somewhat lower efficiencies of shock wave loading and crater creation in comparison with direct laser action are found in the case of double targets where the energy is transferred to the massive target by colliding laser-driven foils or disks. The efficiencies of such a colliding energy transfer are close to 60% for foils and 40% for disks. The experimental results are in a good agreement with two-dimensional hydrodynamic models of shock wave generation under direct laser action and laser-driven macroparticle impact.