Thermal Smoothing of Laser Imprint in Double-Pulse Plasma

The topic of the proposal is a study of the influence of the target illumination by an auxiliary prepulse on a smoothing of spatial non-uniformities in the main laser pulse. In this suggested scheme the prepulse generates an absorption zone near the target surface with non-zero thermal conduction before arrival of the heating pulse. The critical surface position and the size of the absorption zone of the main pulse are controlled by a relative time delay of both laser pulses and by ratio of their intensities. The aim is to assess the conditions under which an optimal smoothing effect takes place. It is expected that by this smoothing process an imprint of a residual nonuniformities on the target surface arising at an application of the optical smoothing methods will be removed, or at least, suppressed. An influence of the prepulse plasma on the effectiveness of the laser-target coupling will be explored. The high power iodine laser system PALS operating at 1.315 ps pulses (energies up to 1 kJ and 0.5 kJ respectively) will be exploited. The density structures in the expanding corona will be identified by the X-ray side-on laser shadowgraphy as well as interferometry. Two-dimensional hydrodynamic simulations of the proposed experiments will be performed. The results obtained from simulations will be post-processed to allow for direct comparison with the results provided by diagnostics from experiments.