Al 2 O 3 anti-reflection coatings with graded-refractive index profile for laser applications

Al2O3 coating is chemically unstable in hot water and transforms into a porous structure with a broadband anti-reflection (AR) property. We investigate the influences of treatment time on the AR property and structure morphology of the Al2O3 coating deposited by electron beam evaporation. Al2O3 coating treated for 7 minutes is found to possess the best AR property with an average reflectance of approximately 0.3% in the wavelength range of 350 nm to 1100 nm. The genetic algorithm simulation shows the treated Al2O3 coating possesses a graded-refractive index profile. The scattering calculation shows a large scattering in the short wavelength range. Moreover, we investigate the laser-resistance of the treated Al2O3 coating, and it shows the potential for application in laser systems.