CONTROL OF THE GROWTH OPTIMUM IN PRODUCING HIGH-QUALITY CAF2 CRYSTALSBY AN IMPROVED BRIDGMAN-STOCKBARGER TECHNIQUE

The axial temperature distribution in an empty crucible and the determ ination of quenched interface within fixed crucible were investigated to find the relationships governing the growing process of CaF2 by Bri dgman-Stockbarger methods. A system of additional molybdenum reflectiv e sheaths was placed into the furnace unit and its effect on the tempe rature field was estimated in order to achieve the growth optimum. A l ong liner into the diaphragm bore of the furnace and a number of thin rings slipped on the crucible stem were found capable to provide a rep roducible optimum on each stage of growing in single and multicamera c rucibles at a relatively low level of power supply. Single and ingroup growth experiments were carried out using high density quenched ingot s purified from oxygen contaminants through high temperature treatment of fluorspar. The properties of the grown crystals were found to depe nd on the degree of the fluorspar purification and on the improvement of the thermal conditions yielding either competitor or laser-grade Ca F2. In multicamera crucibles the crystals grown in the central compart ment are of better characteristics than those in the peripheral ones.