Etching of subwavelength periodic stripes by using a nanosecond laser pulse

In this study, porous silica films, which have particle accumulation microstructure, were prepared using the sol-gel method. For comparison, compact silica films were deposited using the electron-beam-heating method. These films were then irradiated using nanosecond-pulsed laser beams with wavelengths of 1064 and 532 nm. Laser-induced damage thresholds were recorded and the film microstructures, as well as damage photographs, were observed using scanning electron microscopy. The experimental results show that different kinds of stripes formed on the surface of the silica films with particle accumulation structure. A kind of subwavelength periodic straight stripe was observed in the case of the 1064 nm wavelength, whereas another kind of annular stripe around the small damage pits was observed in the case of the 532 nm wavelength.