Effects of molecular vibration on the formation of transient defects during high-power UV laser excitation

Abstract

High-power laser-induced spectrum analyzer was applied to reveal transient material variations in KDP/DKDP crystals. A long-wave pass large-angle filter structure was used to efficiently filter the high-power laser-induced Rayleigh scattering. The Raman spectra excited by a high-power nanosecond laser were compared with that by a low-power continuous-wave (CW) laser. Significant increase of Raman spectra related to the molecular vibration of hydroxyl and hydrogen bonds (1000–3000 cm−1) under high-power laser were obviously detected. The emission spectra in the damaged and undamaged sites were compared. It was found that the intensity of the Raman scattering decreased, and an emission peak at 467 nm was detected after the damage. Moreover, stronger intensity of the stimulated Raman scattering corresponds to higher laser damage threshold. Based on these results, the generation of transient defects was discussed. The irradiation of the high-power laser provided sufficient energy for the intense vibration of hydroxyl and hydrogen bonds, thus breaking bonds and generating transient defects. Furthermore, the energy level of the defects corresponded to the emission peak centered at 467 nm, thereby becoming the precursor of laser damage.