Enhanced Nonlinear Absorption Properties of GaN Nanowires: A Comparison with Bulk GaN

The three-photon coefficient 'γ' of GaN nanowires excited by a 1064 nm laser is reported to be much higher than that of bulk GaN in the picosecond time scale, as mentioned in reference []. In the femtosecond regime, the 3PA coefficients of GaN crystal excited by a 1030 nm laser are an order of magnitude higher than our results. This difference can be attributed to the shorter time scale and the higher concentration of bulk GaN in the crystal. Through numerical comparison and the observation of a large modulation depth, we can speculate that GaN nanowires exhibit better nonlinear absorption performance than GaN crystals. Additionally, we observed saturated absorption phenomena that are not present in bulk crystals. This can be attributed to electron transitions occurring in the quantum confinement effect and the presence of defect states on the surface of the nanowires. This indicates that the nonlinear properties of GaN are enhanced at the nanoscale. The saturation absorption coefficient of GaN nanowires is in the same order of magnitude as materials such as 2D GDY, CH3NH3PbI3 thin film, and graphene-polymer composites excited by picosecond pulses, as mentioned in []. This strongly supports the accuracy of our measurements and the excellent saturation absorption properties of GaN nanowires.