Characterizations of Second-order Nonlinear Optical Susceptibility for ε-phase Gallium Oxide

In this work, we report the second-order nonlinear optical susceptibility χ⁽²⁾ for epsilon phase Gallium Oxide (ε-Ga2O3) thin film on sapphire. ε-Ga2O3 exhibits hexagonal P63mc space group symmetry, which is a non-centrosymmetric structure with non-zero second order susceptibility. By focusing a pulsed laser beam on to a polished ε-Ga2O3 thin film, we collected the generated second harmonic photons with an ultra-sensitive femtowatt photodetector, obtaining effective second-order nonlinear optical susceptibility of χ⁽²⁾ = 4.89×10⁻³ pm/V at wavelength of 800 nm. Two different measurement systems collecting reflected and transmitted photons were applied separately to make the result more convincing. The wavelength dependence from 790 nm to 900 nm and polarization dependence from TM mode to TE mode were measured as well. These results will be helpful for the design and fabrication of Ga2O3 based integrated photonics platform in the infrared-visible spectral range.