Enhanced Three-Photon Absorption and Saturable Absorption in GaN Nanowires: A Comparative Study with Bulk GaN

This research compares the nonlinear optical properties of GaN nanowires and bulk GaN. We found that GaN nanowires exhibit a significantly higher three-photon coefficient (γ) when excited by a 1064 nm laser in the picosecond regime, surpassing the γ of bulk GaN reported in previous studies. While 3PA coefficients for GaN crystals excited by a 1030 nm laser in the femtosecond regime are higher than our findings, this difference can be attributed to the shorter pulse duration and the dominance of bulk GaN properties in the crystal.

Numerical comparisons and measurements of a large modulation depth suggest that GaN nanowires demonstrate superior nonlinear absorption (NLA) performance compared to GaN crystals. Notably, we observed saturated absorption phenomena in GaN nanowires that are absent in bulk crystals. This observation is attributed to electron transitions within the quantum confinement effect and defect states present on the nanowire surfaces.

Our findings highlight the enhancement of GaN's nonlinear properties at the nanoscale. Furthermore, the saturation absorption coefficient of GaN nanowires is comparable in magnitude to materials like carbon dioxide and oxygen when excited by picosecond pulses.