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Optical damage mechanisms in hafnia and silica thin films

Optical damage mechanisms for submicron thick, electron beam deposited HfO2 and SiO2 films on BK-7 substrates have been investigated by monitoring the emission of neutral constituents during excitation with time-delayed pairs of 70 ps laser pulses at a wavelength of 1064 nm. In silica, and probably also HfO2, linear absorption is the mechanism for energy deposition into the films by the laser beams. Sporadic ablation observed for the HfO2 films may be related to optical conditioning of multilayer HfO2-SiO2 high-reflector coatings.