Interfacial Near-Field Activation of Poled Nonlinear Optical Polymers for Second-Harmonic Generation in Gold Nanoprism Hybrids

Abstract

Nonlinear plasmonic nanostructures provide nanoscale optical-field enhancement, but their second-harmonic generation (SHG) efficiencies are often limited by the surface-confined nonlinearity of metals. Here, we overcome this limitation by hybridizing triangular Au nanoprisms with a poled nonlinear optical (NLO) polymer. The SHG conversion efficiency of the hybrid structure is approximately 500 times larger than that of the PMMA-coated Au nanoprism reference under LSP resonance conditions. Wavelength- and thickness-dependent measurements indicate that the enhanced response is consistent with near-field-mediated activation of nonlinear polarization in the poled NLO polymer, with an additional contribution that is consistent with chromophore-resonance-assisted enhancement. Finite-difference time-domain simulations combined with an effective nonlinear susceptibility analysis support a mechanistic model in which the near-field component normal to the upper Au surface can couple efficiently to the large χzzz(2) response of the poled polymer, whereas destructive interference suppresses the far-field contribution from the PMMA-coated Au nanoprism reference. These results establish NLO-polymer/plasmonic hybrids as a versatile platform for enhancing second-order nonlinear responses in metasurfaces.