Slow surface phonon polaritons for sensing in the midinfrared spectrum

We demonstrate a reflection-type sensor in the midinfrared spectra based on resonant excitation of surface phonon polaritons (SPhPs). In this range, SPhPs are characterized by the high density of states associated with slow surface waves that lead to enhanced resonance absorption. Delocalized SPhPs were excited by irradiating TM-polarized light on a one-dimensional grating embedded in a SiC substrate. The sensor response was characterized by changing the refractive index (RI) of a lossless $CO2$ gas. A detection limit of $2×10−5$ RI units was obtained at a wavelength of $11.9μm$⁠.