Combined technique of chemical mechanical polishing and acid etching for improving the laser-induced damage threshold of calcium fluoride

摘要

To further increase the laser-induced damage threshold (LIDT) of calcium fluoride (CaF2), combined technique of chemical mechanical polishing (CMP) and acid etching as a function of removal mechanical defect and impurity contamination was investigated. After CMP process, the surface roughness reduced to Ra 0.68nm, the scratch and subsurface defect were mitigated which rise the LIDT to 8.6 J/cm~(-2). Due to the acid etching, the surface roughness of CaF2 elements increased to Ra 0.8nm, while the LIDT reached 11 J/cm~(-2), benefit from the elimination of impurity contamination. The result laser-induced damage test shows that, comparing to mechanical abrasive polishing (MAP), the LIDT increased by 240% after combined technique, it demonstrated that combined technique is an effective way to improve the resistance of laser damage of CaF2.