Investigation of optical nonlinear properties in semiconductor GaN

The optical nonlinearities of bulk GaN single crystal are investigated by conducting Z-scan experimental measurements, using nanosecond pulses at 532nm. The material’s nonlinear absorptive and refractive optical nonlinearities are determined by measuring the normalized transmittance with and without an aperture in the far field. After simulating the experimental curves, the two-photon absorption (TPA) coefficient, especially the refractive-index change induced by two-photon-excited free carrier, are obtained. The experimental results show that GaN has reverse saturable absorption and self-defocusing effect at 532 nm, indicating this material is a good candidate for future