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Highly reflective LaF(3)/MgF(2) systems for a wavelength of 248 nm on MgF(2) and crystalline quartz substrates were investigated. The influence of laser conditioning on damage threshold and absorptance was remarkable in those coatings that had a high initial absorptance. Monitoring with a laser calorimeter revealed the conditioning effect to be a function of the irradiation dose rather than of energy density or pulse rate. Furthermore, x-ray photoelectron spectroscopy and transmission electron microscopy investigations showed that conditioning induces stoichiometric and structural changes in the multilayers, especially in near-surface sublayers, whereas scanning electron microscopy and atomic force microscopy investigations indicated that the surface remains unchanged.

The laser damage thresholds (LDT) of optical coatings lie, as a rule, markedly below those of the respective bulk materials. This is due to diverse specific realstructure properties with regard to composition, crystallography, microstructure and the physico-chemical structure of the interfaces. These properties depend in a highly complex and sensitive way on the substrate treatment, coating techniques and deposition conditions. With evaporated and sputtered oxide coatings as example, some correlations between structural thin film properties (e.g. crystallography, microstructure, anisotropy, chemical composition, defects) and the ultraviolet (248 nm) or near infrared (1064 nm) laser damage thresholds are discussed with concern to a further increase of the damage resistance. It is evident from data that an approach to the problem requires complex investigations ofthe technology-structure-properties relationships.

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