Absorption of laser radiation in craters on metal targets

An experimental study was made of the integrated (average per pulse) absorptivity of craters on metal targets irradiated with giant ruby laser pulses. The targets were Cu, Al, Mg, Cd, and Sn. Abrupt changes in the absorptivity were due to optical breakdown on the target surface. Under advanced evaporation conditions the absorption by a crater was of the steady-state type: its value was 70% and practically the same for all the investigated materials. The conditions were such that the absorption of laser radiation in the crater, regarded as a geometric cavity, could be ignored. The heat transfer coefficient was also measured.