Polarization-Dependent Third-Order Optical Nonlinearity of ${\rm BaAlBO}_{3}{\rm F}_{2}$ Crystal

We investigated the third-order optical nonlinearity of a new nonlinear optical crystal BaAlBO₃F₂ (BABF) using Z-scan technique with a picosecond 532-nm laser. Polarization-dependent nonlinear refractive index γ of the BABF crystal was measured with an a-cut sample and a sample cut along the type I phase-matching angle for third-harmonic-generation of lasers at 1064 nm (THG-cut). Anisotropy was observed with positive γ values in the range of 10^-16 cm²/W, indicating self-focusing Kerr effects. The measurements agreed well with the theoretical prediction. The corresponding third-order nonlinear optical susceptibility χ_eff⁽³⁾ was estimated to be ~ 10^-14 esu.