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

Abstract

Ablation thresholds and damage behavior of cleaved and polished CaF₂(111) surfaces produced by single shot irradiation with 248 nm/14 ns laser pulses have been investigated using the photoacoustic mirage technique and scanning electron microscopy. The standard polishing yields an ablation threshold of typically 20 J/cm². When surfaces are polished chemo-mechanically the threshold is raised to 43 J/cm². Polishing by diamond turning leads to intermediate values around 30 J/cm². Cleaved surfaces possess no well-defined damage threshold. The damage topography of conventionally polished surfaces 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 cracks and ablation of tiles. The origin of such different damage behavior is discussed.