Three-photon-induced free-carrier absorption in Ga-doped ZnO

Ga-doped ZnO (Ga:ZnO) possesses many advantages due to the unique atomic structure and intriguing physical and chemical properties of Ga, but its optical nonlinear characteristics are rarely studied, so it is difficult to expand its application in the fields of optoelectronics and all-optical components. Here, we examine the optical nonlinearity of Ga:ZnO with the help of a theoretical quantitative model of three-photon-absorption (3PA)-induced free carrier absorption (FCA) and free carrier refraction (FCR). 3PA-induced FCA was examined and distinguished successfully from 3PA through z-scan measurements. Experimental results prove that Ga:ZnO exhibits strong nonlinear absorption at a wavelength of 800 nm. The FCA cross section and 3PA coefficient are σ_α=3×10−¹⁷ cm² and β₃=2.5×10−⁴ cm³/GW², respectively, and the optical limiting related to FCA was also experimentally examined. This study of the optical nonlinear properties of Ga:ZnO may provide a strategy for applying this material in the fields of optoelectronics and photonic devices.