Mapping Phonon Polaritons with Visible Light

TL;DR

This paper demonstrates a method to map and analyze phonon polariton modes in nanostructures using confocal Raman microscopy with visible and near-IR light, revealing detailed light-matter interactions.

Contribution

It introduces a novel approach to visualize and reconstruct phonon polariton eigenmodes in nanostructures through Raman intensity analysis.

Findings

All Raman-active bulk phonon modes couple to SPhP modes.

Polarizability selection rules dominate the coupling mechanism.

The method enables 3D reconstruction of PhP eigenmodes.

Abstract

Phonon polaritons (PhPs) are hybrid photon-phonon waves which enable strong light-matter interactions and subdiffractional confinement, potentially empowering applications in sensing, nonlinear optics and nanoscale energy manipulation. In this work, we use confocal Raman microscopy to investigate the coupling between bulk phonon modes and localized surface phonon polariton (SPhP) modes in indium phosphide (InP) nanopillars and 4H-silicon carbide (4H-SiC) gratings. The Raman intensity within the nanostructures is described in terms of the SPhP eigenmodes and used to reconstruct the field intensity, providing a method to map SPhP eigenmodes using visible and near-IR light. Our results indicate that, contrary to expectation, all Raman-active bulk phonon modes of InP and 4H-SiC couple to the localized SPhP modes. Further, we confirm that polarizability selection rules form the predominant coupling mechanism between phonons and SPhP modes, with electron-phonon coupling playing a role for certain phonon modes (A1(LO) and E1(TO) in 4H-SiC). These observations provide a method for extending Raman studies of PhP modes to achieve full 3D reconstruction of the PhP eigenmodes and visualize light-matter interactions within nanostructures, thus advancing Raman scattering as a technique for understanding PhP modes.