New Photographic Technique for Observing Bulk Laser Damage

摘要

A damage site camera was developed to record the onset of bulk laser damage in materials. The camera images and magnifies the damage track using forward-scattered laser light. Employing this camera we can detect the presence of very small (10 m) damage sites with densities as low as 10/cc. The camera is used at oblique incidence to the part being tested. We have observed discrete damage sites generated within the bulk of some materials, such as silicate glass, fluorophosphate glass, and KDP crystals, by 1-ns 1064-nm laser pulses. The energy fluxes at which bulk damage is initiated are in the range of 2 to 20 J/cm exp 2 , much lower than the fluxes required to cause damage by intrinsic processes. Small foreign inclusions (1 m diameter) are the cause of these low bulk damage thresholds. The inclusions density varies from 10 exp 7 /cc to less than 10/cc. At threshold the damaged volumes are small (1 to 5 min diameter) and thus, can be observed most easily by their forward-scattered light. Several photographs are shown to illustrate the onset of bulk laser damage in fluorophosphate glass and KDP crystals. (ERA citation 06:017078)