Femtosecond Z-scan measurement of GaN

Nonlinear refractive index $n_2$ of GaN was measured for the below-band-gap ultraviolet (UV) wavelength region using Z-scan techniques with femtosecond UV pulses. A large nonlinear refractive index of ${\text{−2.9±1.2×10}}^{\text{−12}} {\mathrm{cm}}^{\mathrm{2}}\mathrm{/W}$ was obtained at a wavelength of 368 nm. The distribution of $n_2$ versus wavelength was found to be consistent with a model described by the quadratic Stark effect, which is the dominant factor contributed to the nonlinear refractive index near the band gap. Our experiments show that GaN is an excellent nonlinear material with large negative $n_2$ in the UV region.