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Fundamental aspects of multishot laser damage are considered: thermal instability in an optical medium due to pulse-to-pulse accumulation of absorbing defects,mechanisms of laser induced defect generation. Effective methods of suppressing a defect formation to increase laser damage resistance are discussed and illustrated by experimental data for various type optical materials.

The values of the damage thresholds of some alkali halide crystals, sapphire and fused quartz at λ = 0.266 μm are presented. The role of electron avalanche in the damage of real wide-gap dielectrics in the UV region is discussed. Some peculiarities of the interaction of intense UV radiation with dielectrics (nonlinear absorption, photoionization of impurities, self-focusing and others) are considered. Experiments on laser damage induced by two synchronous, crossed laser beams with different frequencies (λ1 = 1.06 μm and λ2 = 0.266 μm) are described. This method makes it possible to establish the influence of “seeding” electrons on the development of laser-produced damage, as well as to determine if the damage mechanisms are similar at different frequencies. In order to record directly and estimate concentrations of the free carriers excited by UV laser radiation, d.c. photoconductivity experiments have been carried out.

CO2‐laser produced damping of electron‐hole drop (EHD) luminescence in Ge at laser intensities of 104 to 5 × 106 W/cm2 is reported. The observed effect is explained to be due to heating of the EHD by 10.6 μm radiation and driving of e‐h plasma by phonon wind generated during absorption and relaxation of hot nonequilibrium carriers.