Competitive Effects of Surface Plasmon Resonances and Interband Transitions on Plasmon-Enhanced Second-Harmonic Generation at Near-Ultraviolet Frequencies

The competition between plasmonic resonances and noble-metal interband transitions at near-ultraviolet (NUV) frequencies complicates nonlinear conversion processes at nanoscales. Here, we experimentally design a highly enhanced and reproducible plasmon-enhanced second-harmonic generation (PESHG) platform suitable for NUV frequencies by constructing three-dimensional silver mushroom arrays. The SHG emission from proposed platforms involved in geometrical asymmetry greatly outperforms that from unpatterned metallic films. Studies among mushroom arrays with various geometric parameters and weight ratios of component materials enable us to distinguish characteristics exhibited by plasmon-driven enhancement and interband-transition suppression, such that competitive effects on PESHG can be readily observed and quantitatively measured. Our work may provide insights for understanding the physical mechanism governing plasmon-enhanced nonlinear optical processes and may help attain efficient nonlinear wavelength conversions for quantum-optical and nonlinear metamaterial applications.