New Experimental Platforms for Molecular Polaritonics

Polaritons are hybrid light-matter states that arise from strong interactions between the confined electromagnetic field of an optical cavity and an ensemble of intracavity molecules. Molecules under such strong cavity coupling appear to demonstrate distinct reactivity and photochemistry from molecules in free space, but the mechanisms and scope of these phenomena remain poorly understood. I will discuss new experimental approaches that my lab is taking to investigate the behavior of simple benchmark cavity-coupled systems, with the goal of understanding exactly how and when reactive trajectories may be influenced by strong light-matter interactions.

While polaritons are now well-established in solution-phase and solid-state systems, they had not been previously reported in isolated gas-phase molecules, where attaining sufficiently strong light-matter interactions is a challenge. We access the strong coupling regime in an intracavity cryogenic buffer gas cell optimized for the preparation of simultaneously cold and dense ensembles. We report proof-of-principle demonstrations of rovibrational strong coupling in methane and rovibronic strong coupling in molecular iodine. In ongoing work, we are harnessing this infrastructure as a testbed for fundamental studies of the nonlinear spectroscopy, photophysics, and chemistry of polaritonic states.

We are also searching for signatures of cavity-altered dynamics in benchmark condensed-phase molecular systems using ultrafast spectroscopy. I will touch on our work on both solution-phase bimolecular reaction dynamics under vibrational strong coupling and excited state relaxation dynamics in thin films under electronic strong coupling. I will also detail our various approaches to track the dynamics of these species without confounding spectroscopic artifacts, and comment on when we need to invoke quantum optics versus classical cavity physics to explain our observations.

Speaker: Marissa Weichman, Princeton University