Abstract: The interaction of nanosecond ultraviolet laser light with bulk optical materials is discussed for the example of fluoride crystals. Absorption and thermoelastic response of the crystals are related to the laser damage threshold. It is shown that this threshold is most limited by defects resulting from surface preparation. Cleavage of crystals produces atomically flat terraces with highest damage thresholds ($GRT 40 J/cm$+2$/ for ns-pulses at 248 nm) while cleavage steps and tips result in a dramatic local reduction of damage resistivity. Conventional polishing introduces contamination, scratches and dislocations yielding damage thresholds of typically 10 to 15 J/cm$+2$/. Advanced preparation techniques like chemo-mechanical polishing and precision grinding provide surfaces with a damage threshold uniform over large areas that is close to that of cleavage terraces. In all cases the damage threshold is determined by light absorption of defect-induced electronic states energetically located in the band gap of the insulator. Band gap states in calciumdifluoride are investigated by ultraviolet photoelectron spectroscopy and luminescence spectroscopy and surface quality is monitored by scanning electron and scanning force microscopy. Laser damage thresholds obtained for differently prepared surfaces are related to their structural and electronic properties and the primary mechanisms of energy uptake from the laser light are discussed.!23
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机译：摘要：以氟化物晶体为例，讨论了纳秒紫外激光与块状光学材料的相互作用。晶体的吸收和热弹性响应与激光损伤阈值有关。结果表明，该阈值受表面处理所产生的缺陷的最大限制。晶体的切割产生原子上平坦的平台，具有最高的损伤阈值（对于248 nm的ns脉冲，$ GRT为40 J / cm $ + 2 $ /），而切割步骤和尖端会导致局部的损伤电阻率显着降低。常规抛光会引入污染，划痕和位错，从而导致损坏阈值通常为10至15 J / cm $ + 2 $ /。化学机械抛光和精密研磨等先进的制备技术可为表面提供接近于分裂平台的大面积均匀损伤阈值。在所有情况下，损伤阈值都是由能量吸收的，能量位于绝缘体带隙中的缺陷诱发的电子态决定的。通过紫外光电子能谱和发光光谱研究二氟化钙中的带隙态，并通过扫描电子和扫描力显微镜来监测表面质量。为准备不同的表面获得的激光损伤阈值与它们的结构和电子特性有关，并讨论了从激光吸收能量的主要机理。23
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