Coupling effect of multi-wavelength lasers in damage performance of multilayer mirrors at 355 nm and 1064 nm

Abstract

Coupling effect between 355 nm laser and 1064 nm laser in damage initiation and morphology formation are investigated on two different coatings prepared with Hf/SiO₂ and HfO₂/SiO₂ respectively. It was found that materials had little influence on the couple effect. When extra 1064 nm pulse energy is low, 355 nm laser induced damage thresholds of both coatings increase because of laser conditioning and then when 1064 nm pulse energy is high enough, 355 nm LIDTs decreased. Damage morphologies are also studied to explore the damage mechanism at respective wavelength. For the entirely different electric field distribution, 355 nm laser induced damages are mainly from nanometer-sized absorbers at upper interfaces while initiators for 1064 nm laser locate at substrate-coating interface or substrate subsurface. Under simultaneous illumination, the sensitive defects are still the precursors, but the damages are more catastrophic compared with damages induced by 355 nm laser only and they also show representative damage characteristics induced by single laser, namely 355 nm laser induced small pits and 1064 nm laser induced large delamination. Further studies also show that delamination area grows with the increase of pit numbers induced by 355 nm laser at fixed 1064 nm laser fluence. A possible mechanism was proposed to interpret observed delamination area growth phenomenon.