Damage to wide-gap insulators by ultraviolet laser radiation

An investigation was made of laser damage to many wide-gap transparent insulators at the wavelength of the fourth harmonic of a neodymium laser (0.266 μ). Substantial variations in the damage threshold were observed for most materials, indicating that impurities and defects influence the damage process. The possible mechanisms for self-focusing of radiation in sapphire are discussed. An analysis is made of the possible role of the avalanche ionization mechanism in damage to fused quartz, LiF, and CaF₂. Conclusions are drawn on the most suitable materials for ultraviolet optics at high radiation powers.