Multi-photon excitation UV emission by femtosecond pulses and nonlinearity in ZnO single crystal

Optical nonlinearities and multi-photon ultraviolet (UV) excitation in ZnO single crystal were investigated by the z-scan method utilizing an intense femtosecond (fs) laser at different wavelengths. Based on the analysis of the experimental results at different excitation wavelengths near 800 nm, nonlinear optical effects that may emerge under an intense field are attributed to be responsible for the efficient two-photon absorption process under detuned excitation.