Polariton assisted photoemission from a layered molecular material: role of vibrational states and molecular absorption

Abstract

The way molecules absorb, transfer, and emit light can be modified by coupling them to optical cavities. The extent of the modification is often defined by the cavity–molecule coupling strength, which depends on the number of coupled molecules. We experimentally and numerically study the evolution of photoemission from a thin layered J-aggregated molecular material strongly coupled to a Fabry–Perot microcavity as a function of the number of coupled layers. We unveil an important difference between the strong coupling signatures obtained from reflection spectroscopy and from polariton assisted photoluminescence. We also study the effect of the vibrational modes supported by the molecular material on the polariton assisted emission both for a focused laser beam and for normally incident excitation, for two different excitation wavelengths: a laser in resonance with the lower polariton branch, and a laser not in resonance. We found that Raman scattered photons appear to play an important role in populating the lower polariton branch, especially when the system was excited with a laser in resonance with the lower polariton branch. We also found that the polariton assisted photoemission depends on the extent of modification of the molecular absorption induced by the molecule–cavity coupling.