Characterizations of the nonlinear optical properties for (010) and (2¯01) beta-phase gallium oxide.

We report, for the first time, the characterizations on optical nonlinearities of beta-phase gallium oxide (β-GaO), where both (010) β-GaO and (2¯01) β-GaO were examined for two-photon absorption coefficient, Kerr nonlinear refractive index, and their polarization dependence. The wavelength dependence of two-photo absorption coefficient and Kerr nonlinear refractive index were also estimated by a widely used analytical model. β-GaO exhibits a two photon absorption (TPA) coefficient of 1.2 cm/GW for (010) β-GaO and 0.6 cm/GW for (2¯01) β-GaO. The Kerr nonlinear refractive index is -2.1 × 10 cm/W for (010) β-GaO and -2.9 × 10 cm/W for (2¯01) β-GaO. In addition, β-GaO shows stronger in-plane nonlinear optical anisotropy on (2¯01) plane than on (010) plane. Compared with GaN, TPA coefficient of β-GaO is 20 times smaller, and the Kerr nonlinear refractive index of β-GaO is also found to be 4-5 times smaller. These results indicate that β-GaO have the potential for ultra-low loss waveguides and ultra-stable resonators and integrated photonics, especially in UV and visible wavelength spectral range.