Laser damage and ablation of differently prepared CaF2(111) surfaces

Ablation thresholds and damage behavior of cleaved and polished CaF2(111) s urfaces produced by single shot irradiation with 248 nm/14 ns laser pulses have been investigated using the photoacoustic mirage technique and scannin g electron microscopy. The standard polishing yields an ablation threshold of typically 20 J/cm(2). When surfaces are polished chemo-mechanically the threshold is raised to 43 J/cm(2). Polishing by diamond turning leads to in termediate values around 30 J/cm(2). Cleaved surfaces possess no well-defin ed damage threshold. The damage topography of conventionally polished surfa ces shows ablation of flakes across the laser heated area with cracks along the cleavage planes. In the case of chemo-mechanical polishing only a few cracks appear. Diamond turned surfaces show small optical absorption, but c racks and ablation of tiles. The origin of such different damage behavior i s discussed.