Process for growing of optical fluorite single crystals

Abstract

The present invention relates to the technical field of preparing artificial calcium fluoride (optical fluorite) single crystals by growing from a melt by the directed crystallization and by using a seed crystal. The aim of the invention is to obtain oriented single crystals with a small deviation from the given direction. The technical result is achieved by the selection of a concrete technological mode in which the leading role has a period for melting of seed crystal. The optical fluorite single crystals are grown by crystallization on the oriented seed inserted into the central part of a bottom of crucible. Before the beginning of crystallization the crucible with a melt is maintained in a melt zone for a time that is sufficient for the homogenization of the whole melt and in this time the bottom part of a seed crystal appears below a melt zone. Subsequently, the crucible with a melt and with a seed crystal is moved from the melt zone into the annealing zone with the given speed. The method differs from the prior art in that the crucible with a melt is kept in a melt zone for 24–48 hours, then the crucible is relocated upwards into the melt zone at a speed of 5–50 mm/hr to a level making 10–40% of the height of the seed crystal within the melt zone. The crucible is kept in such condition from 10 about 20 minutes, and then the crucible is moving downwards out of the melt zone in accordance to the given mode of crystallization.