Probing polaritons in the mid- to far-infrared

The long free-space wavelengths associated with the mid-to far-infrared spectral range impose significant limitations on the form factor of associated optic and electro-optic components. Specifically, current commercial optical sources, waveguides, optical components (lenses and waveplates), and detector elements are larger than the corresponding diffraction limit, resulting in reduced image resolution and bulky optical systems, with deleterious effects for a number of imaging and sensing applications of interest to commercial, medical, and defense related arenas. The field of nanophotonics, where the ultimate objective is to confine and manipulate light at deeply subwavelength, nanometer length scales, offers significant opportunities to overcome these limitations. The demonstration of nanoscale optics in the infrared can be achieved by leveraging polaritons, quasiparticles comprised of oscillating charges within a material coupled to electromagnetic excitations. However, the predominant polaritonic materials and the characterization techniques and methods implemented for measuring these quasiparticles in the mid-to far-IR require a different approach with respect to similar efforts in the ultraviolet, visible, and near-IR. The purpose of this tutorial is to offer an overview of the basic materials, tools, and techniques for exciting, manipulating, and probing polaritons in the mid-to far-infrared wavelength range, providing a general guide to subwavelength and nanoscale optics for those entering this exciting and burgeoning research field. Published under license by AIP Publishing.