Optical erosion of germanium single crystals caused by CO2 laser pulses

The characteristics of surface erosion of germanium make this semiconductor a suitable material for laser optics. The results are reported of an investigation of the morphology of the optical damage and the generation of carriers below the damage threshold. The results obtained indicate that thermal breakdown on the surface of germanium is preceded by a thermal instability which develops at nonequilibrium carrier clusters. This conclusion is supported by the results of measurements of the threshold power of single pulses: the power corresponding to the onset of erosion can be twice as high for laboratory samples prepared differently from commercial samples.