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The impurity content of synthetic calciumdifluoride (fluorite, CaF2) single crystals produced for optical applications in the deep ultraviolet (DUV) and infrared (IR) spectral regions are investigated by luminescence and absorption spectroscopy. Lead, oxygen, and rare earth (RE) ions, namely, trivalent (Ce3+, Pr3+, Sm3+, Eu3+, Gd3+, Tb3+, Dy3+, Ho3+, Er3+, and Yb3+) and divalent (Eu2+) are identified as common impurities. RE ions are dominating impurities in the IR grade sample and the impurity concentration for this sample is found to be about 100 times higher than the one for DUV samples. Due to the strongly reduced RE luminescence background, we additionally identify lead and oxygen in DUV grade crystals. Remarkable differences in the luminescence spectra are found when comparing DUV grade crystals from different sources.

Damage behaviour and thresholds for single 248 nmr14 ns excimer laser pulses have been investigated for single Ž . crystals of CaF and BaF with 111 surface orientation. The probe beam deflection technique was applied as a sensitive 2 2 tool for detecting the onset of single-shot damage. Below the plasma threshold, we observed one-and two-photon absorption for CaF and BaF , respectively. When testing the influence of different polishing techniques, we found the lowest 2 2 thresholds for conventional hard-polish. Advanced methods as ductile machining or chemical polishing lead to a distinct increase in damage threshold up to and even better than what is observed for cleaved surfaces. SEM investigations of irradiated areas show that damage preferably takes place at residual steps or other structural defects.