Enhanced Two-Photon Absorption and Saturable Absorption in Gallium Nitride Nanowires for Ultraviolet Light Limiting

Chi-Kuang Sun reported the saturated absorption of bulk gallium nitride under 371.2 nm laser excitation. The maximum normalized transmittance was 1.02, while our maximum transmittance was 1.8. The nanowire structure significantly enhanced the single-photon absorption of 355 nm laser, which has been rarely reported in other materials. Photons with a wavelength of 266 nm have a high energy of 4.66 eV, and the material exhibits significant linear absorption. Few materials exhibit two-photon absorption effects, with only diamond and silica in the ultraviolet range having high transmittance. Due to the wide bandgap of gallium nitride, the nanowires exhibit superior two-photon absorption light-limiting performance under 266 nm laser irradiation, and their two-photon absorption coefficient can be comparable to high-content bulk single crystals under similar conditions. Interestingly, we discovered a slight saturable absorption effect, which can become significant by adjusting the excitation pulse width.