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Influence of the test parameters on LIDT determination for single and multiple laser irradiations in optical components in nanosecond regime

LIDT specification of optical components is now widely required to perform laser systems where high power and/or long term life are the critical points. Depending on the application, the system has to resist to single shot with the highest possible intensity as in the NIF and Megajoule projects. Otherwise a compromise on LIDT value is necessary to permit a great shot number (109 shots) for example for spatial applications. In order to characterize the LIDT and long term life of components, specific laser induced damage setups are used. The test configuration is close to the final application (wavelength, pulse duration, beam shape), but most often, parameters as spatial and temporal beam profiles are different. Otherwise, different test procedures as raster scan method or statistic procedure are used to determine the behavior of material, which induces additional differences between the obtained LIDT values. For practical reasons (cost and size of sample) the beam size is most often smaller than in the final application. Because of these parameters misfit, differences are highlighted between the setups of different laboratories even using the same ISO norm. In this context differences with the final system has to be expected in terms of LIDT. A good knowledge of the influence of the different parameters on the final result is required to reduce the LIDT uncertainty. In this paper, to illustrate the purpose, we will present examples of significant influence induced by test sampling, beam diameter, spatial and temporal profile applied to non-linear crystal and silica.