Dose-dependent optical properties and laser damage of helium-implanted sapphire

Abstract

A series of single crystalline Al2O3 samples are implanted with He+ ions at different nominal fluences up to 1 × 1018 ions/cm2 at room temperature. The microstructure evolution and optical properties as well as laser-induced damage threshold are investigated. Optical microscopic images show that the density and amount of defects increase with increasing implantation fluence. In addition, atomic force microscopic images indicate that the surface morphologies have changed distinctly when the fluence reaches 5 × 1017 ions/cm2 and above. After helium implantation, broad purple and green–yellow absorption bands as well as an obvious photoluminescence band at 330 nm are observed, respectively. With the increase of implantation fluence, the intensities of absorption bands increase greatly, whereas the intensity of the photoluminescence band decreases and tends to saturation. The original strong infrared band shifts and broadens with increasing implantation fluence. The mechanism for the shift and broadening of the infrared band is discussed. After laser irradiation, it is found that the implantation fluence has great effect on the laser-induced damage threshold, which decreases significantly from 5.43 J/cm2 to 4.62, 3.71, 2.64, and 1.80 J/cm2 with increasing implantation fluence. A mechanism for the degradation of laser damage resistance is presented.