Nanosecond laser-induced surface damage and material failure mechanism of single crystal CaF2 (111) at 355 nm

Abstract Surface damage and material failure mechanism of CaF 2 single crystal by 355 nm/6.8 ns laser pulses are systematically studied in this work. Surface damage characteristics, such as damage threshold, damage growth threshold, damage growth laws and damage growth coefficient of CaF 2 crystal are carefully studied. Surface material cracking and local material vitrification (from CaF 2 crystal to defective CaF 2-x materials) are revealed. Material decomposition, oxidation and formation of Ca 0 , Ca 2+ and (F − -F − ) centers in surface layer are illustrated. Laser-driven thermal accumulation and thermal-stress gradient in CaF 2 crystal are calculated and discussed based on the theory of Fourier heat conduction and thermal-elastic constitutive equations. Theory analysis suggests that the material failure process in CaF 2 crystal is mainly driven by significant thermal stress gradient. Thermal gradient induce the material decomposition and local vitrification in CaF 2 crystal. Combined results on surface damage and material failure behavior are beneficial to understand nanosecond laser-driven modifications and damage in fluoride crystals at ultraviolet wavelength.