LASER-DAMAGE OF CLEAVED AND POLISHED CAF2 AT 248-NM

We investigated the surface damage of CaF2 induced by irradiation with 248 nm/14 ns laser pulses. Experiments were carried out in single sho t mode in air. The photoacoustic deflection technique was utilized for in situ damage detection and irradiated spots were inspected by scann ing electron microscopy. Fracture along the natural cleavage planes wa s observed. Comparison of cleaved and polished samples in connection w ith modelling the thermoelastic response of the crystal during damage reveals that polishing causes enhanced surface absorption, Damage topo graphy at the periphery of the irradiated spots was used to obtain a r ough estimate of the temperature rise leading to fracture. Electron mi croscopy shows surface modifications of weakly irradiated spots where no ablation or cracking could be detected.