Linear and nonlinear optical properties of ZnO nanorod arrays

Polarization-dependent linear absorption, second-harmonic generation (SHG) and 3rd-order nonlinearities of well-aligned ZnO nanorod arrays have been investigated with ps pulses. The depressed spectral width and the enhanced intensity of reflective SHG along the long axis of ZnO nanorods were observed by using p-polarized pulses, which is explained by the optical confinements. The nonlinear absorption coefficient measured with s-polarization reached the maximum 4.0$\times $10$^{4}$cm/GW at the wavelength $\sim $750\,nm, which revealed a large two-photon resonance absorption attributed to the quantum confined exciton when the polarization is vertical to the long axis of ZnO nanorod.