Light-matter interaction: from weak to strong coupling

MPSD Seminar

Date: Sep 21, 2016
Time: 11:00 AM - 12:00 PM (Local Time Germany)
Speaker: Xiaolan Zhong
ISIS & icFRC, University of Strasbourg and CNRS
Location: CFEL (Bldg. 99)
Room: Seminar Room IV, O1.111
Host: Andrea Cavalleri

When an exciton transition and a resonant optical mode exchange energy faster than any competing dissipation process, it can lead to light-matter strong coupling. This brings about interesting properties possessed by neither the original exciton nor the optical mode and leads to new possibilities such as enhanced conductivity of organic semiconductors. In this case, the enhancement stems from the delocalized nature of the hybrid states over the spatial extent of the optical mode which is also expected to affect energy transport according to recent theoretical studies.

In this talk, it is interesting to consider how such hybrid states would affect energy transfer between donor and acceptor molecules. Strong coupling could provide an alternate effective path for energy transfer in analogy with chemically bridged donors and acceptors where the linker mediates the interactions by an effective overlap between the wave functions of both the donor and the acceptor. In the strong coupling case, it is the polaritonic states which are by construction either donor or acceptor-like that mediates the interactions in the system due to their delocalized nature. We present direct evidence of enhanced non-radiative energy transfer between two J-aggregated cyanine dyes strongly coupled to the vacuum field of a cavity. Excitation spectroscopy and femtosecond pump-probe measurements show that the energy transfer is highly efficient when both the donor and acceptor form light-matter hybrid states with the vacuum field.