Here, we review the progress and most recent advances in phonon-polaritonics, an emerging and growing field that has brought about a range of powerful possibilities for mid- to far-infrared (IR) light. These extraordinary capabilities are enabled by the resonant coupling between the impinging light and the vibrations of the material lattice, known as phonon-polaritons (PhPs). These PhPs yield a characteristic optical response in certain materials, occurring within an IR spectral window known as the reststrahlen band. In particular, these materials transition in the reststrahlen band from a high-refractive-index behavior, to a near-perfect metal behavior, to a plasmonic behavior – typical of metals at optical frequencies. When anisotropic they may also possess unconventional photonic constitutive properties thought of as possible only with metamaterials. The recent surge in two-dimensional (2D) material research has also enabled PhP responses with atomically-thin materials. Such vast and extraordinary photonic responses can be utilized for a plethora of unusual effects for IR light. Examples include sub-diffraction surface wave guiding, artificial magnetism, exotic photonic dispersions, thermal emission enhancement, perfect absorption and enhanced near-field heat transfer. Finally, we discuss the tremendous potential impact of these IR functionalities for the advancement of IR sources and sensors, as well as for thermal management and THz-diagnostic imaging.

Abstract. The field of plasmonics has the potential to enable unique applications in the midinfrared (IR) wavelength range. However, as is the case regardless of wavelength, the choice of plasmonic material has significant implications for the ultimate utility of any plasmonic device or structure. In this manuscript, we review the wide range of available plasmonic and phononic materials for mid-IR wavelengths, looking in particular at transition metal nitrides, transparent conducting oxides, silicides, doped semiconductors, and even newer plasmonic materials such as graphene. We also include in our survey materials with strong mid-IR phonon resonances, such as GaN, GaP, SiC, and the perovskite SrTiO 3 , all of which can support plasmon-like modes over limited wavelength ranges. We will discuss the suitability of each of these plasmonic and phononic materials, as well as the more traditional noble metals for a range of structures and applications and will discuss the potential and limitations of alternative plasmonic materials at these IR wavelengths.

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Although concussed players may be asymptomatic upon return to play, the residual effects of concussion on the skills required for batting may still be present. Further work is needed to clarify the mechanism through which batting performance after concussion is adversely affected and to identify better measures to use for return-to-play decisions.