As the field of nonlinear plasmonics advances, it is important to understand how induced nonlinear fields are enhanced by localized surface plasmon resonances (LSPRs) and controlled by the polarization of incident light. This is especially the case when metal nanostructures have multiple LSPRs in different wavelength regions that can enhance both the incident light and the electric field induced by nonlinear polarization. We have experimentally and theoretically studied the second harmonic (SH) responses from gold nanocrescent arrays with polarization dependent LSPRs in visible and near-infrared wavelength regions to investigate their roles for the most fundamental nonlinear optical process. The wavelength and polarization dependent SH responses show that the effects of LSPRs at the fundamental and SH wavelengths as well as nanocrescent symmetry are important in governing the SH generation process. The experimental findings were corroborated by finite difference time-domain calculations coupled with a nonlinear hydrodynamic model. Our calculations also show that the incident polarization angle dependence of SH signals is very strongly sensitive to nanoscale variations in the nanocrescent’s shape. Our findings in this study will contribute to future development in utilizing tunability of multiple LSPRs in more complicated metal nanostructures and the development of new plasmonic devices based on nonlinear optical phenomena in subwavelength.

Understanding the second harmonic responses of gold nanocrescent arrays

ACS Fall 2021

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