Speaker
Description
Strong light-molecule coupling has led to a new class of matter at nanoscale, due to its tunable hybridization of molecular excitations and photons known as polaritons. Because of the confined geometry that yields the collective nature, molecular polaritons create a new paradigm of molecular relaxation and radiative processes, i.e., reaction activity and light-induced exotic phases. These brought up great challenges for optical spectroscopy. The multidimensional spectroscopy, by introducing several delays and gates between laser pulses, is powerful for studying the molecular relaxation and photochemistry. This delivers a versatile tool for a real-time monitoring of nonequilibrium molecular dynamics, but not clear yet for polaritons. The collective interactions result in the long-range quantum coherence, which creates new relaxation channels and spectroscopic probes of molecular polaritons.
In this talk, I will present an overview of our recent works on the multidimensional spectroscopy for molecular polaritons. We developed a microscopic theory for the 2D spectroscopy of molecules in microcavities, using the density matrix and Langevin equation. A new capability of resolving multiple channels and timescales of polariton dynamics with high time-frequency scale is demonstrated. The results manifest coherent couplings in a trade-off with the dark states. The dark states show a high mode density and localized nature, which have significant contribution to the population and coherence of polaritons. Our work provides a power theory and approach for a unified understanding of the spectroscopic signals measured in recent experiments on molecular polaritons.
