Preparation of CaF₂ precursors for laser grade crystal growth

Abstract 

The expansion of commercial excimer lasers has increased the need of high-quality optics manufactured from CaF₂. The key technical parameters, affecting the long-term quality of CaF₂ excimer laser optics, are controlled by the purity of the raw material. The new purifying techniques provide 99.99% purity of the starting material which rises up to 99.999% into the grown crystals. However, the techniques are rather expensive which leads to a significant rise in the price of the final crystal product. The present paper describes an alternative highly effective and relatively low-cost technique providing a precise control over a set of preparatory and purifying procedures and crystal growth. Using an original apparatus for electro-chemical grinding of the thermo-broken starting material, the grained product, uncontaminated by unintentional impurities, may be highly purified by two complementary methods to produce precursors used for UV- and laser-grade CaF₂ crystal growth.