Morphology study and threshold measurement of laser induced damage of nano-porous antireflective silica thin films in nano- and femtosecond pulse regimes

Laser induced damage threshold (LIDT) of nano-porous antireflective silica thin films is measured using 10 ns laser pulses at λ = 532 nm. The thin films are prepared by dip-coating of BK7 substrates and then drying them by three different heating methods, to see how their LIDT and transmission are affected. Furthermore, using SEM imaging, the morphology of the laser induced damages is inspected and compared to those of similar samples, previously irradiated by femtosecond laser pulses at λ = 800 nm. The images evidently show that in the regions damaged by nanosecond pulses, the silica nanoparticles are melted and fused to each other, while in the samples irradiated by femtosecond pulses, the silica nanoparticles are sputtered and dispersed around, in the damaged area. The SEM images clearly demonstrate the different damage mechanisms involved in the nanosecond and femtosecond regimes of interaction. (author)