Laser Damage Phenomenology in Materials

Abstract

Improvements in laser technology must be accompanied by concomitant improvements in optical materials. The presence of both macroscopic and microscopic defects contribute significantly to the evolution of damage in optical components. It is well known that macroscopic defects such as scratches, polishing pits, and inclusions at the surface of a material will tend to scatter incident light from the sample. Absorption and local heating will occur at cavities or near inclusions of varying dielectric constant, often resulting in catastrophic surface breakdown on bulk material failure. The presence of microscopic defects such as vacancies, interstitials, or “impurities” in a crystal may effect the absorption of light by causing a local perturbation of the lattice spectrum. Larger defects such as dislocations, voids, inclusions, and grain boundaries often serve as scattering centers or absorbers, depending upon dimensions, charge configuration, the wavelength of light, and the relative absorption efficiencies. Other defects, introduced either during material growth or as a result of exposure to ionizing radiation (e.g., electronic traps, color centers, impurity-vacancy pairs) can substantially affect absorption in both the visible-UV region and the infrared region of the spectrum.