Influence of the surface and subsurface contaminants on laser-induced damage threshold of anti-reflection sub-wavelength structures working at 1064 nm

Abstract

The anti-reflection sub-wavelength structures (ARSS) was proposed to be a promising approach for the antireflection (AR) laser application due to the higher laser-induced damage threshold (LIDT) and better spectral performance. In this paper, we designed and fabricated two-dimensional periodic ARSS, and investigated the influence of surface and subsurface contaminants on the LIDT of ARSS. It is found that the photoresist residues on the surface of as-produced ARSS directly induce laser damage at a fluence of 16 J/cm2. Oxygen plasma cleaning can remove most of the photoresist residues, however, the re-deposition layer formed during the ion beam etching process are detrimental enough to trigger laser-induced damage at a relatively low fluence of 24 J/cm2. An optimal ultrasonic cleaning was developed to etch the re-deposition layer in the ARSS and the LIDT of the ARSS was significantly increased to 56 J/cm2, which is comparable to LIDT of the bare fused silica substrate. It illustrated that the surface and subsurface contaminants affect the LIDT of ARSS significantly. Moreover, the damage behaviors of ARSS were further investigated utilizing artificial nano-sized gold particles as the surface contaminants compared to the AR coating and bare fused silica substrate. The LIDT is influenced significantly by nano-sized gold particles for ARSS due to the electric field enhancement, while the LIDT decreased slightly in the case of AR coating and bare fused silica substrate. It verified that the surface and subsurface contaminants are much more critical key precursor to the laser-induced damage of ARSS.