About the author: Ryan Kowalski is a fourth-year graduate student pursuing a PhD in Interdisciplinary Materials Science under the direction Dr. Josh Caldwell. Using infrared spectroscopy, the Caldwell group investigates the optical properties of semiconductor materials for optoelectronic devices. Ryan’s recent publication in Advanced Optical Materials characterizes the anisotropic dielectric functions of 2D van der Waals materials, HfS2 and HfSe2 . The crystal anisotropy of these polar dielectric materials gives rise to a spectral region, the Reststrahlen band, that can host light-matter quasiparticles called surface phonon polaritons (SPhPs). SPhPs allow for extreme confinement of light beyond the diffraction limit, an essential component for nanophotonic devices. Furthermore, it is found that HfS2 and HfSe2 have extremely large Reststrahlen bands that span most of the far-infrared, a region of the electromagnetic spectrum that has traditionally been restricted due to materials constraints. This work paves the way for a potentially new class of optical infrastructure in the far-infrared.