Joshua D. Caldwell
U.S. Naval Research Laboratory
Mid-IR to THz Polaritonics: Realizing Alternative IR Materials
Location: EB1 Room 1011
Friday, February 5th 2016 - 11:00 am
The field of nanophotonics is based on the ability to confine light to sub-diffractional dimensions. Up until recently, research in this field has been primarily focused on the use of plasmonic metals. However, the high optical losses inherent in such metal-based surface plasmon materials has led to an ever-expanding effort to identify, low-loss alternative materials capable of supporting sub-diffractional confinement. Beyond this, the limited availability of high efficiency optical sources, refractive and compact optics in the mid-infrared to THz spectral regions make nanophotonic advancements imperative. One highly promising alternative are polar dielectric crystals whereby sub-diffraction confinement of light can be achieved through the stimulation of surface phonon polaritons within an all-dielectric, and thus low loss material system. Due to the wide array of high quality crystalline species and varied crystal structures, a wealth of unanticipated optical properties have recently been reported. This talk will discuss recent advancements from our group including the realization of localized phonon polariton modes, the observation and exploitation of the natural hyperbolic response of hexagonal boron nitride. Beyond this, methods to improve the material lifetime and to induce additional functionality through isotopic enrichment and hybridization of optical modes will also be presented.
Dr. Joshua Caldwell was awarded his bachelors of Chemistry from Virginia Tech in 2000 before heading to the University of Florida where he received his PhD in Physical Chemistry in 2004. There he used magnetic resonance methods to investigate electron-nuclear spin coupling within low-dimensional quantum wells and heterostructures. He accepted a postdoctoral fellowship at the Naval Research Laboratory, using optical spectroscopy as a means of understanding defects within wide-band gap semiconductors. He was transitioned to permanent staff in 2007, where he began work in the field of nanophotonics, investigating coupling phenomena within plasmonic materials. More recently, Dr. Caldwell merged his prior work in wide band gap semiconductor materials with his efforts in nanophotonics, leading to his efforts to use undoped, polar dielectric crystals for low-loss, sub-diffraction optics. Dr. Caldwell recently finished a sabbatical at the University of Manchester with Prof. Konstantin Novoselov, investigating the use of van der Waals crystals such as hexagonal boron nitride for mid-IR to THz nanophotonics.