This paper considers the effects of a 249nm excimer pulse on CaF2 substrates and is concerned with both surface damage and bulk colouration processes.

The effect of different polishing procedures on the surface damage threshold of CaF2 has been investigated.

CaF2 has been shown to develop colour centres under prolonged U.V. irradiation. A technique has been developed to monitor the transient excited states created in the bulk material when irradiated with a 25ns excimer pulse. This involves a simultaneously pumped dye laser pulse probe operating at the absorption wavelengths of the excited species. From the results information about the photon absorption cross sections can be derived, the concentration of defect states at any time during the excimer pulse may be estimated and a knowledge of the maximum safe fluence levels established.