Dynamics of Vibration-Cavity Polaritons*

Coupling vibrational modes to optical cavities results in vibration-cavity polaritons which can modify vibrational coherence and energy dynamics. Ultrafast infrared spectroscopy has been used to investigate vibration-cavity polaritons. We recently reported time resolved IR pump-probe studies on strongly-coupled vibration-cavity polaritons for tungsten hexacarbonyl (W(CO)₆) in hexane in a Fabry-Pérot cavity [1]. The results demonstrated that while much of the response is due to so-called reservoir or uncoupled excited state absorption as well as polariton contraction, a component of the observed signals is due to polariton state evolution. We observe saturable absorption as nearly complete polariton contraction not only in pump probe measurements but also in single pulse studies.[2] 2DIR spectroscopy was used to provide evidence of hybrid light-matter polariton evolution and clear indications of direct excitation of dark states..[3] We have further expanded the investigation of vibrational dynamics for strongly coupled vibration-cavity polaritons to W(CO)₆ in other solvents and to nitroprusside (Fe(CN)₅NO^2- in methanol. We explore salient features of the transient response, especially at short delay times, which show aspects of the response that are due to polaritons and are distinguished from uncoupled higher order excitations.

[1] A. D. Dunkelberger, B. T. Spann, K. P. Fears, B. S. Simpkins, and J.C. Owrutsky, Nat. Comm. 7, 13504 (2016).
[2] A.D. Dunkelberger, R.Davidson, W. Ahn, B.S. Simpkins, and J.C. Owrutsky, J. Physi. Chem. A 122, 965 (2018).
[3] B. Xiang, R. F. Ribeiro, A. D. Dunkelberger, J. Wang, Y. Li, B.S. Simpkins, J.C. Owrutsky, J. Yuen-Zhou, W. Xiong, PNAS 115, 4845-4850 (2018).