Experimental demonstration of laser damage caused by interface coupling effects of substrate surface and coating layers.

The laser damage resistance of the coatings for high-power laser systems depends greatly on the surface quality of the substrate. In our work, experimental approaches were employed to understand the interface coupling effect of the substrate surface and coatings on the laser resistance of the coatings. A 1064 nm anti-reflection (AR) coating was deposited by an e-beam coater onto fused silica with and without micro-scale pits (structural defects). The micro-scale pits were precisely fabricated by femtosecond laser processing to prevent the emergence of subsurface cracks. Different deposition temperatures were characterized in order to verify the intensity of the interface coupling effect of the substrate and coating layers. Our experimental results indicate that impurities that are introduced in the finishing process, shifted to the substrate surface, and aggregated during the heating process, play a much more crucial role than structural defects (length: ∼7  μm; width: ∼3  μm; depth: ∼0.8  μm) in the laser-induced damage process. By effectively reducing the intensity of the interface coupling effect, the e-beam AR coatings, whose laser-induced damage resistance was closed to the bare substrate, was prepared.