Calcium fluoride crystal formation method using Bridgeman-Stockbarger process, comprises cooling crystal at predetermined rate by moving water-cooled rod at predetermined speed

摘要

A calcium fluoride crystal in the temperature range 1100-700degreesC, is cooled at a rate of 1.3-2.0degreesC/hr. The constant axial temperature drop with a gradient 20-50degreesC/m, is provided in the absence of radial gradient, by moving a water-cooled rod (11) down with the speed of 0.8-1.4. The water- cooled rod is arranged at distance of 0.3-0.4 from the height of a heater in annealing zone (3). An Independent claim is also included for calcium fluoride crystal.