Fe-related defect-induced strong broadband two-photon absorption and nonlinear refraction transients in β -Ga2O3 for ultrafast all-optical switching

Investigating the broadband nonlinear optical response and related dynamic mechanisms in the wide-bandgap semiconductor gallium oxide is crucial for ultrafast photonic applications. In this study, transient absorption spectroscopy was used to probe the metal-doping effect on the bound-electron nonlinear optical response. Fe doping was found to significantly enhance the nondegenerate two-photon absorption, a remarkably large imaginary component of the figure of merit, indicating potential applications for nonlinear absorption-based all-optical switching. Analysis of the optical polarization dependence of carrier absorption, combined with carrier-induced nonlinear refractive effect, demonstrated that Fe doping modulates the carrier lifetime and enables the transformation of phase symbols, establishing mechanisms for the implementation of dual-channel optical switching. An energy-level model based on photoluminescence elucidates the nonlinear optical modulation mechanism of Fe-related defect states on bound electrons and carriers. This study serves as a valuable reference for the design of gallium-oxide-based waveguides and all-optical switching materials.