Optical coating degradation under laser irradiation can take several forms. Perhaps the most common that is not due to particulates is thermal breakdown, caused by heating of the coating to a catastrophic failure induced by local melting, delamination, evaporation, or some other change. We demonstrate that micromachined dielectric membranes show strong differences in their hydroxyl signatures as measured by Fourier-transform IR spectroscopy. The changes correspond to regions of high fluence from a Nd:YAG laser. It is found that the absorption peaks associated with OH decrease after laser treatment, indicating a reduction in the number of film hydroxyl groups.
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