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Based on exact symmetry considerations one can show that a cubic system is always optically isotropic. Nevertheless even a perfectly cubic crystal such as CaF2can show small optical anisotropy when interacting with light. Resolving this seeming contradiction leads to a phenomenon called spatial dispersion, which is an enhancement of optical anisotropy. While the initial tiny anisotropy is caused by the symmetry breaking of light, the enhancement that makes the effect observable is provided by the vicinity of a strong absorption. In semiconductors such an absorption is mainly given by the band gap but in an ionic crystal such as CaF2the bound electron-hole pair, a deep excitonic two-particle bound state, is an additional strong absorption causing response functions to diverge as (−0)−1in its vicinity, where 0is the bound state energy. We show that the exciton dispersion is able to explain in all details the optical anisotropy observed in CaF2including the spatial-dispersion-induced birefringence, the so-called “intrinsic birefringence.” As opposed to normal birefringence, the effect in CaF2does not show up at large wavelengths and has seven optical axes instead of one.© 2003 Society of Photo-Optical Instrumentation Engineers.

Large calcium fluoride (CaF2) single crystals are required for the fabrication of lenses in so‐called wafer‐steppers of future IC‐lithography technologies operating at 193 nm and 157 nm. Numerical simulation plays an important role to design an adequate growth setup and processing conditions for the growth of high quality crystals. An important issue is the consideration of the internal heat transfer by radiation in the semitransparent CaF2during the crystal growth process. Results of the numerical modeling of the heat transport are presented, which are obtained by using the software package CrysVUn++ with different models considering the internal heat transport in CaF2. To improve the availability of experimental data on CaF2bulk growth, an especially designed R&D‐facility was built. This growth system is equipped with a variety of in‐situ measurement systems to detect the temperature distributions in the crystal and melt region. Calculated temperature distributions are compared with experimental data. Also first results on single crystal growth will be reported.