Hyperspectral Infrared Imaging of Surface Phonon-polaritons in SrTiO3

Polaritons have a demonstrated impact on nanophotonic applications in the midinfrared through visible spectral range. Surface phonon-polaritons (SPhPs) offer a way to bring the potential of polaritons to the longer infrared wavelengths. Strontium titanate (STO) is a perovskite polar dielectric with diverse technologically advantageous properties and it can support SPhPs in a uniquely broad spectral range of the far infrared. Despite these advantages, STO has mostly been overlooked as a nanophotonic material. In this work we investigate SPhP propagation in STO in the far-infrared through midinfrared spectral range using broadband, near-field nanospectroscopy. We developed a tabletop, laser sustained plasma light source that enabled us to obtain amplitude and phase resolved hyperspectral line scan maps of SPhPs across the surface of the STO sample. Analytical modeling of experimental data reveals the dispersion characteristics of SPhPs in STO. This work establishes STO as a platform for perovskite-based broadband far-infrared and terahertz nanophotonics