Optical damage of nonlinear crystals, thin films, and substrates can limit the performance of bulk and fiber lasers, OPAs, OPOs, and OPGs. The study of optical damage is far from a science - it is largely a study of phenomenology. It is a difficult topic because there is a wide variety of damage mechanisms and a number of masking nonlinear processes. Reported damage thresholds for the most common of optical materials, fused silica, vary over orders of magnitude. We are performing damage measurements under conditions that allow measurement of the true, or intrinsic, damage thresholds of silica, nonlinear crystals, laser crystals, and thin films. We find the damage threshold of silica is identical within 1% for all optical quality silica samples. For nanosecond pulses the threshold is determined by irradiance rather than fluence, and damage occurs at 500 GW/sq cm. For picosecond pulses the damage irradiance is slightly higher. Further, the surface damage irradiance is equal to the bulk damage irradiance if the sample is properly polished. We will extend these measurements to nonlinear crystals, laser host crystals, and thin films.
We offer advice on designing and interpreting damage measurements, including understanding and modeling the important roles of stimulated Brillouin scattering, self focusing, electron avalanche, dopants, and impurities.