  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.
