Pre-plasma effect on energy transfer from laser beam to shock wave generated in solid target

Efficiency of the laser radiation energy transport into the shock wave generated in layered planar targets (consisting of massive Cu over coated by thin CH layer) was investigated. The targets were irradiated using two laser pulses. The 1 omega pulse with the energy of similar to 50J produced a pre-plasma, imitating the corona of the pre-compressed inertial confinement fusion target. The second main pulse used the 1 omega or 3 omega laser harmonics with the energy of similar to 200J. The influence of the pre-plasma on parameters of the shock wave was determined from the crater volume measurements and from the electron density distribution measured by 3-frame interferometry. The experimental results show that the energy transport by fast electrons provides a definite contribution to the dynamics of the ablative process, to the shock wave generation, and to the ablation pressure in dependence on the target irradiation conditions. The strong influence of the pre-plastna on the investigated process was observed in the 1 omega case. Theoretical analysis supports the explanation of experimental results. (C) 2014 AIP Publishing LLC.