Nonlinear Absorption and Saturable Absorption Properties of GaN Nanowires for Optical Limiting and Ultrafast Photonics

Nonlinear Absorption and Saturable Absorption Properties of GaN Nanowires for Optical Limiting and Ultrafast Photonics

This study focuses on the synthesis and characterization of gallium nitride (GaN) nanowires for their potential in optical limiting and ultrafast photonic applications. We successfully synthesized GaN nanowires using the chemical vapor deposition method. Subsequently, we conducted a comprehensive investigation of their nonlinear absorption properties across the ultraviolet (UV), visible, and near-infrared (NIR) spectral regions utilizing a picosecond pulsed laser system.

Our experimental results reveal the presence of strong two-photon absorption (TPA) at various excitation wavelengths, specifically 266 nm, 355 nm, and 532 nm. Furthermore, we observed three-photon absorption (3PA) at 532 nm, highlighting the intricate interplay of nonlinear optical processes within these nanostructures.

Significantly, we also detected broadband saturable absorption (SA) in the GaN nanowires. This phenomenon is particularly prominent in the UV-Vis wavelength range, exhibiting substantial modulation depths of 56% and 45%, respectively. The observed SA, combined with their strong TPA and 3PA, suggests GaN nanowires can function as effective optical limiters, especially in high-intensity light environments.

To delve deeper into the underlying mechanisms, we analyzed the electron transition pathways responsible for the observed nonlinear absorption phenomena. Further insights were gained through numerical simulations, which allowed us to quantify critical parameters such as saturable absorption intensity, two-photon absorption coefficient, and three-photon absorption coefficient.

Our findings unequivocally demonstrate the exceptional potential of GaN nanowires as both broadband optical limiting materials and saturable absorbers, particularly in the UV-Vis region. This research paves the way for their integration into advanced optical limiting devices and ultrafast photonic applications, including mode-locking, pulse shaping, and optical switching.