Nd: YAG laser-irradiation-induced damage to LiNbO3and KDP

It is shown that internal damage in LiNbO3and KDP occurs at the same or lower levels of irradiation than surface damage. This is found in crystals used as frequency doublers and Pockels cells as well as in samples having different orientations. It is recommended, therefore, that samples that have suffered surface damage be thoroughly inspected internally before being repolished and reused. Internal filamentary damage in LiNbO3is shown to be composed of a series of very fine nearly planar cracks, which intersect to form one or more long lines having diameter . When illuminated with visible light, diffraction effects make these lines appear blurred and give the impression of a tube of damaged material. Scanning electron micrographs of surface damage are included in this paper in order to show the very different characteristics of entrance and exit face damage and to reveal the importance of thermal effects as at least one cause of laser-induced damage.