Abstract
A comparative study of optical breakdown in several CVD and HPHT single crystals has been performed with IR femtosecond pulses, which are widely used for diamond bulk processing. The breakdown thresholds for the diamond surface and bulk are measured and then compared with the morphology of the laser-modified regions formed during the breakdown process. The highest level of the bulk breakdown threshold is found to be typical for the HPHT crystals, whereas for the CVD crystals breakdown threshold varies greatly. It is assumed that certain defects assembled in microbunches of various sizes may decrease considerably the diamond breakdown threshold. The nature of these defects and the mechanism of the threshold reduction are under study.
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