Optical strength of some materials illuminated over relatively large areas

The optical strength of BaF₂, NaCl, and CaF₂ crystals as well as of KI and KU quartz glasses was measured at the wavelength of 1.06 μ. The investigated crystals and KI glass were found to have high concentrations of absorbing inclusions in the bulk. A study was made of the dependence of the surface optical strength on the size of the illuminated spot in the range of relatively large spots (up to 1 cm in diameter). The surface strength of BaF₂, NaCl, and CaF₂ crystals was considerably less than the strength of quartz glasses and of K-8 glass. The surface damage was explained by a probabilistic model of local damage at absorbing inclusions.