关键词: 氟化钙晶体, 坩埚下降法, 晶体退火, 透过率, 光学均匀性, 应力双折射

Abstract: Calcium fluoride (CaF₂) crystal is a kind of excellent optical material. In this investigation, an 8-inch(20.32 cm) CaF₂ single crystal was grown by the Bridgman method. The crystal has complete appearance and no macroscopic defects such as cracking and scattering. After orientational cutting, a transparent cylindrical crystal blank with diameter of 40 mm×6 mm was obtained, the blank sample was annealed twice and then polished to obtain the final sample. The ultraviolet-visible-near infrared transmittance, optical homogeneity, and average stress birefringence were measured. The results show that the transmittance at 200 nm reaches 90%. The average stress birefringence is less than 0.5 nm/cm. The optical homogeneity reaches 2.63×10^-6.

Key words: CaF₂ crystal, Bridgman method, crystal annealing, transmittance, optical homogeneity, stress birefringence