Absorption in metallic targets irradiated by 50 ps laser pulses at intensities below 1012W/cm2

Abstract

The energy reflected from plane metallic targets irradiated by 50 ps Nd-laser pulses, in the intensity range 1010-1012 W/cm2, has been measured. The authors find that for different conditions of incident energy and spot size, the target absorption is well correlated with incident intensity. The presence of radiation diffused out of the collecting lens angle when the spot size is very small can be accounted for by a simple geometrical interpretation. The experimental results at intensities below 1011 W/cm2 are in good agreement with a model in which absorption takes place through the high collision rate of the degenerate electron gas at the solid density; the validity of this model is confirmed by the measured blue-shift of the reflected radiation.