Abstract:

Calcium fluoride (CaF₂) crystals have good optical properties and chemical stability, and are often used as substrate materials in extreme edge optical window scenes. It is noteworthy that as one of the key properties of UV laser window materials, the radiation damage resistance of CaF₂ crystal increases too fast due to the cleavage effect, and the actual damage threshold is much lower than the theoretical value, which cannot meet the needs of UV high-power laser devices, and is the main factor limiting its application in high-power UV lasers. In this study, material composition design was used to introduce F_i^- by doping inert rare earth Y³⁺, and the cluster effect between Y³⁺ and F_i^- was used to increase the bonding number between the cleavage planes, so as to enhance the interlayer bonding force, reduce the cleavage effect and raise the damage threshold. CaF₂ crystals doped with Y³⁺ were prepared under the same condition by using a porous crucible, and their optical quality, mechanical properties and thermal properties of the doped CaF₂ crystals were characterized and analyzed. The experimental results show that appropriate amount of Y³⁺ doping has little effect on the optical and thermal properties of CaF₂ crystals, such as transmittance, thermal expansion coefficient and thermal conductivity, and does not affect the performance of CaF₂ crystals. However, the influence on mechanical properties, such as shear strength, is relatively prominent. When the optimized doping concentration is 0.36% (in atom), the shear strength is increased by 68.4%, and the corresponding laser induced damage threshold of Y:CaF₂ crystal is increased by 166%.

Key words: CaF₂ crystal, cluster structure, shear stress, damage characteristic