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In the application of high-power lasers, damage to active laser materials, and to components of laser system, generally determines the limit of useful laser performance. Accordingly, there is great interest in reducing the susceptibility of optical elements ot damage. Damage in transparent dielectrics arises from three major causes, particulate inclusions or microinhomogeneities in the material, self-focusing within the materials, and surface damage due to plasma formation. The state of understanding of these phenomena, and the thresholds observed, where they have been determined, will be discussed. Dependence on pulse length will also be considered. Although most of the research accomplished to date on laser damage has concentrated on Nd-glass, the advent of very high-powered gas lasers has stimulated interest in the development of damage resistant component materials for use in the ir. Crystalline dielectrics appear to be the most likely candidate materials for ir windows. Nonlinear optics materials are particularly susceptible to damage, since they are generally exposed to high intensity radiation. Asa final item, damage in thin film dielectric coatings are considered.

Nonlinear refractive-index coefficients of 11 fluoride crystals were measured at 1064 nm using time-resolved interferometry. A simple empirical expression is given for the index nonlinearity in terms of the d-line refractive index and Abbé number which agrees with measured values for both fluoride crystals and optical glasses and which can be used to estimate index nonlinearities. Since the nonlinear indices of several fluoride crystals are among the smallest reported for solids, these materials are of interest for transmitting optical components in high-power laser systems where self-focusing is important.

For laser beams of large aperture with power far above the critical power for self-focusing, nonlinear propagation instabilities lead to the growth of small-scale variations in intensity and phase. We report measurements of the growth rate for interference fringes in unpumped ED-2 laser glass as a function of fringe spacing and intensity. Calculations based on the simplest form of linearized small-scale instability theory agree approximately with the measured rates, and a more complete linearized treatment predicts the growth rates within experimental error.

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