ELSEVIER Beam Interactions with Materials&Atoms Laser-damage of cleaved and polished CaF, at 248 m-n

We investigated the surface damage of CaF2 induced by irradiation with 248 nm/14 ns laser pulses. Experiments were carried out in single shot mode in air. The photoacoustic deflection technique was utilized for in situ damage detection and irradiated spots were inspected by scanning electron microscopy. Fracture along the natural cleavage planes was observed. Comparison of cleaved and polished samples in connection with modelling the thermoelastic response of the crystal during damage reveals that polishing causes enhanced surface absorption. Damage topography at the periphery of the irradiated spots was used to obtain a rough estimate of the temperahire rise Ieading to fracture. Electron microscopy shows surface modifications of weakly irradiated spots where no ablation or cracking could be detected.