Third-harmonic-generation nonlinear absorption coefficient of 70% deuterated DKDP crystal

Abstract

The nonlinear optical absorption (NLA) of 70% deuterated DKDP crystals that were cut along different directions and annealed under different temperatures was measured at the third-harmonic-generation (THG) wavelength (355 nm) of a nanosecond Nd:YAG laser by using the Z-scan method. The nonlinear absorption (NLA) coefficient β was obtained by fitting the experimental data. According to the fitting result, the nonlinear absorption at 355 nm is identified to two-photon absorption. Results indicate that the β value of the type I THG direction (5.6 × 10−2 cm/GW) was close to that of the type II THG direction (5.2 × 10−2 cm/GW). Moreover, the β values of both types were obviously below the data of the Z-axis direction (7.2 × 10−2 cm/GW). Our experiments showed that thermal annealing can effectively decrease NLA coefficients. At the optimum annealing temperature of 140 °C, the β of the type II THG sample was 2.4 × 10−2 cm/GW, which was only 46% that of the unannealed crystal. This work will aid the THG application of DKDP crystals in inertial confinement fusion systems.