Optical resistance and spectral properties of anti-reflective coatings deposited on LBO crystals by ion beam sputtering

Abstract

The nonlinear LBO (LiB3O5) crystal is widely used in many Nd : YAG, Yb : KGW and Nd : YLF lasers in order to generate higher optical harmonics. However, the most limiting factor in such applications is the optical resistance of their coated surfaces described by the so-called Laser Induced Damage Threshold (LIDT) parameter. In this work we investigate the “fatigue” (multi-pulse) behaviour of LIDTs in LBO crystals coated with different types of (single AR@355 nm and triple AR@355+532+1064 nm wavelength) anti-reflective coatings while optimising the refractive index designs and selecting appropriate sub-layer materials. All the coatings were produced of different oxide materials (ZrO2, Al2O3, SiO2) and ZrO2-SiO2 mixtures by using the ion beam sputtering (IBS) deposition technique. The optical damage resistance of both fixed and transient refractive index coatings is of special interest. Besides the spectral properties, the resistance to laser irradiation is characterised at the wavelength of 355 nm with laser pulses of nanosecond duration. The conclusions are drawn about the AR coated LBO with the most successful designs by the means of optical resistance.