Polaritons are quasiparticles of mixed optical-material nature that provide an opportunity for designing new properties in material systems. Coupling vibrational modes to optical cavities results in vibration-cavity polaritons that have been shown to modify chemical reaction rates and branching ratios. Our group has been investigating whether cavities alter transient properties such as relaxation of molecular vibrations, which might explain the modified chemistry. We have used infrared pump-probe as well as 2D IR measurements to investigate vibrational polaritons formed by strong coupling to the CO vibrational band of tungsten hexacarbonyl (W(CO)6) and to the NO band of nitroprusside (Fe(CN)5NO2-). The results demonstrate that most of the response is due to reservoir or uncoupled excited state absorption as well as polariton contraction. In addition, we observe novel photonic behavior for strong pumping in which saturable absorption results in near complete polariton contraction. In addition, we have analyzed the early time response which we attribute to spectral diffusion of the dark or reservoir states. In another area of research. we have demonstrated active tuning of surface phonon polaritons (SPhPs), which have potential applications in active nanophotonics and molecular sensing. SPhPs are narrow absorption bands that depend on phonon properties produced in nanostructures of polar dielectrics such as silicon carbide. These resonances are like plasmon bands but narrower because they depend on vibrational rather than electronic properties and are more intrinsically in the infrared region. SPhPs can be tuned by injecting carriers via ultraviolet, above band gap excitation because the carriers couple with the phonon vibrations, which we have demonstrated via infrared transient absorption for SiC nanopillar arrays and GaN films
Jeff Owrutsky is head of the Spectroscopy and Dynamics Section in the Chemistry Division of the U.S. Naval Research Laboratory (NRL) in Washington DC. He got his BA at Brandeis University and his PhD in Chemistry at University of California, Berkeley. After a postdoc at the University of Pennsylvania, he became an NRC Postdoc at NRL. His research has included ultrafast gas phase photochemistry, solution ultrafast studies of photochemistry and vibrational relaxation, transient studies of photocatalysts and optical diagnostics of catalysts and high temperature solid oxide fuel cells. Current areas of interest include nanophotonics and nanomaterials, plasmonics and phonon polaritons, and spectroscopy and dynamics of strongly coupled systems, including vibration-cavity strong coupling. He has over 150 papers and proceedings and several patents.