Patent ID: 7014703
Filing Date: 2006-03-21
Classification: C30B

Abstract:
1. A method of preparing a metal fluoride single crystals having reduced stress birefringence, said method comprising the steps of: growing a metal fluoride single crystal according to any crystal growth method known in the art, cleaning and polishing the grown crystal to remove surface imperfections, and subjecting the cleaned and polished crystal to a secondary annealing process to thereby form a metal fluoride single crystal having reduced stress birefringence where the secondary annealing process comprises: placing the crystal in a holder in a furnace; raising the crystal to a temperature in the range of 50–150° C. below the crystal's melting temperature; cooling the crystal from a temperature in the range of 50–150° C. below its melting point of to a temperature in the range of 250–500° C. below its melting point at a rate in the range of 1–10° C./hour, followed by cooling the crystal to a temperature in the range of 500–750° C. below its melting point at a rate in the range of 5–20° C./hour, followed by cooling the crystal to a temperature in the range of 750–1000° C. below its melting point at a rate in the range of 10–40° C./hour, and cooling the crystal to ambient temperature at a rate of 20–50° C./hour.