Dispersion of two-photon absorption and nonlinear refraction in <b> <i>β</i> </b>-Ga2O3 from 350 to 515 nm
Xiao Tian, Hai‐Shuang Lu, Tian‐Xiang Qian, Wenfa Zhou, Junyi Yang, Xifeng Yang, Sheng Ju, Zhongguo Li, Yinglin Song
Abstract
We report the wavelength dependencies of the two-photon absorption coefficients β as well as the nonlinear refractive index n2 of undoped β-Ga2O3 single crystal in the spectral range 350–515 nm (0.51 &lt; Ephoto/Eg &lt; 0.75). Femtosecond Z-scan measurements show that n2 decreases monotonically toward the shortwave side, while the maximum value of n2 is 5.0 × 10−19 m2/W near half of the bandgap, Eg. Interestingly, a second upward trend in β was observed when the incident photon energy is larger than 0.6Eg, indicating the impact of additional inter-band transitions with higher energy. A higher-energy band-to-band transition around 6.0 eV was determined by both femtosecond nondegenerate two-photon absorption spectroscopy and ab initio calculations. Our results could provide guidance for designing nonlinear β-Ga2O3 photonic devices in the UV-visible spectral range.