BK7 glass substrates were precleaned by different cleaning procedures before being loaded into a vacuum chamber, and then a series of plasma ion cleaning procedures were conducted at different bias voltages in the vacuum chamber, prior to the deposition of 532-nm antireflection (AR) coatings. The plasma ion cleaning process was implemented by the plasma ion bombardment from an advanced plasma source. The surface morphology of the plasma ion-cleaned substrate, as well as the laser-induced damage threshold (LIDT) of the 532-nm AR coating was investigated. The results indicated that the LIDT of 532-nm AR coating can be greatly influenced by the plasma ion cleaning energy. The plasma ion cleaning with lower energy is an attractive method to improve the LIDT of the 532-nm AR coating, due to the removal of the adsorbed contaminations on the substrate surface, as well as the removal of part of the chemical impurities hidden in the surface layer.
Al2O3 monolayer films were deposited on fused silica substrate and K9 glass substrate by electron-beam deposition. Annealing as a general post-treatment was used to enhance the quality of the Al2O3 coatings. The optical properties of the films were analyzed from the transmission spectra of the samples. The composition of the samples before and after annealing were measured by X-ray photoelectron spectroscopy (XPS). According to the analysis of the results, it can be found that the oxidation degree of the coatings increases after annealing in O2 inside coating chamber. The laser-induced damage thresholds of the Al2O3 films can be increased after the annealing process. Finally, the damage morphologies of the Al2O3 coatings were analyzed.
Hafnia-silica (HfO2/SiO2) mixed thin films with a wide range of different compositions have been deposited on fused silica substrate by E-beam co-evaporation. The change in composition is achieved by changing the deposition rates of individual materials. The transmittance spectra are measured by the spectrometer, and then the refractive indexes are calculated with Essential Macleod. The vertical uniformity and grain structure of the films are analyzed by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD), respectively. The experimental results demonstrate that the coatings have good uniformity, and all the films are amorphous except the pure HfO2 film. In addition, the mixed coating with about 16.85% SiO2 content has a higher refractive index than the pure HfO2 coating.