Second harmonic generation from strongly coupled localized and propagating phonon-polariton modes

TL;DR

This study explores second harmonic generation in silicon carbide nanopillar arrays, revealing how strong coupling affects nonlinear optical responses and interference effects between different polarization contributions.

Contribution

It provides the first experimental demonstration of second harmonic generation from strongly coupled localized and propagating phonon polariton modes, highlighting nonlinear response asymmetries.

Findings

Strong coupling modifies the nonlinear optical response.

Interference effects significantly influence second harmonic signals.

Asymmetry in SHG reveals complex mode interactions.

Abstract

We experimentally investigate second harmonic generation from strongly coupled localized and propagative phonon polariton modes in arrays of silicon carbide nanopillars. Our results clearly demonstrate the hybrid nature of the system's eigenmodes and distinct manifestation of strong coupling in the linear and nonlinear response. While in linear reflectivity the intensity of the two strongly-coupled branches is essentially symmetric and well explained by their respective localized or propagative components, the second harmonic signal presents a strong asymmetry. Analyzing it in detail, we reveal the importance of interference effects between the nonlinear polarization terms originating in the bulk and in the phonon polariton modes, respectively.