Surface and bulk absorption in CaF2 at 193 and 157 nm

Comprehensive calorimetric absorption measurements were performed for CaF2 crystals at irradiation wavelengths 193 and 157 nm. By using samples with different thickness a separation of surface and bulk absorptance could be achieved and thus, single- and two-photon absorption coefficients could be determined for both wavelengths. For the surface absorptance, a dependence of the polishing grade of the sample was observed at 193 nm. The investigation of earlier reported repetition rate dependencies of the effective two-photon absorption coefficient at 193 nm was extended up to a repetition rate of 2.8 kHz. In contrast to the measurements at 193 nm, no such dependence at all could be found at 157 nm. Both results support already proposed models of the absorption mechanisms in wide band-gap materials.