Resonant enhancement of second harmonic generation in the mid-infrared using localized surface phonon polaritons in sub-diffractional nanostructures

TL;DR

This study demonstrates significant enhancement of mid-infrared second harmonic generation in SiC nanopillars by resonantly exciting localized surface phonon-polaritons, with results influenced by crystal structure and phonon mode interactions.

Contribution

It reveals how localized surface phonon polaritons can be used to enhance nonlinear optical responses in nanostructures, highlighting the interplay with crystal phonon modes.

Findings

Strong SHG enhancement at monopole mode in SiC nanopillars

Dependence of SHG on resonant frequency and crystal structure

Coupling effects between phonon polaritons and zone-folded phonon modes

Abstract

We report on strong enhancement of mid-infrared second harmonic generation (SHG) from SiC nanopillars due to the resonant excitation of localized surface phonon-polaritons within the Reststrahlen band. The magnitude of the SHG peak at the monopole mode experiences a strong dependence on the resonant frequency beyond that described by the field localization degree and the dispersion of linear and nonlinear-optical SiC properties. Comparing the results for the identical nanostructures made of 4H and 6H SiC polytypes, we demonstrate the interplay of localized surface phonon polaritons with zone-folded weak phonon modes of the anisotropic crystal. Tuning the monopole mode in and out of the region where the zone-folded phonon is excited in 6H-SiC, we observe a prominent increase of the already monopole-enhanced SHG output when the two modes are coupled. Envisioning this interplay as one of the showcase features of mid-infrared nonlinear nanophononics, we discuss its prospects for the effective engineering of nonlinear-optical materials with desired properties in the infrared spectral range.