Observation of Neutron-Induced Absorption and Phase-Mismatch for Quasi-Phase-Matched Second Harmonic Generation in Congruent Lithium Niobate

Abstract

We report an experimental observation of radiation-induced optical absorption in undoped congruent lithium niobate (LiNbO3) crystals between the 190 nm and 3200 nm wavelength range. It was found that high-dose (up to 288 Gy) gamma rays did not significantly affect the optical absorption of LiNbO3 during that wavelength range. However, upon the order of 1016 cm−2 neutron irradiation, the change in the absorption coefficient was up to 0.6 cm−1 at a wavelength of 532 nm and remained after 13 days in the dark at room temperature. The nonlinear optical performance was characterized by conducting third-order quasi-phase-matched second harmonic generation in neutron-irradiated periodically-poled LiNbO3, showing that the phase-matching condition was altered, and the conversion efficiency was still comparable with a non-irradiated one.