Tuning of Phonons and Surface Phonon Polaritons

Plasmonic materials can be used for surface enhanced infrared absorption, a particularly useful technique for chemical sensing applications, but these materials typically suffer from high optical losses, which result in broad optical resonances. In contrast, surface phonon polaritons (SPhPs) have much lower losses, resulting in narrower resonance bands. In particular, our group is investigating polar dielectric inorganic crystals that have mid-IR Reststrahlen bands, frequency ranges where the crystals’ optical constants resemble metals and can support SPhP resonances. Currently, our efforts are focused on studying the optical properties of calcite (CaCO3) crystals in the mid-IR. We have used a focused ion beam to directly nanostructure the surface of calcite in order to generate SPhPs (or more specifically for calcite, hyperbolic phonon polaritons) for sub-diffraction optical confinement of mid-IR incident light. The results of these studies will allow us to better understand how to tune these phonon polaritons in a broader spectral range with different inorganic materials and provide a basis for exploring how these resonances interact with other chemical systems.