Thermal smoothing of laser imprint using low-intensity prepulse or low-density porous matter

An overview of earlier studies of laser imprint treatment employing a low-intensity prepulse of the iodine laser PERUN is complemented by recently performed much more sophisticated prepulse experiments (so far only preliminary) using the powerful PALS laser facility. Subsequently, much closer attention is paid to the alternative approach to laser imprint treatment - application of layers from a low-density porous matter. Interaction of PALS beam with low-density foam targets and acceleration of Al foils by the pressure of heated porous matter have been investigated, both experimentally and theoretically. The experimental results are in a good agreement with our two-dimensional hydrodynamic calculations that do not take fine structure of foam material into account. The only exception is the case of the thinner PVA foam where the code predicts much higher rear side velocities due to heating and expansion of the foil material. It indicates that heat flux is overestimated to a certain extent in the simulation code. Consequently, heat conductivity value should be revised in the case when the foam homogenization is not complete during the heat wave propagation. A simplified analytical model has been presented that does not include heating and expansion of the foil on the target rear side. The derived rear side velocities agree well with the experiment and it is another indication that foil is accelerated without significant expansion. (author)