Whispering gallery mode resonators with J-aggregates

We have studied the optical properties of a hybrid system consisting of cyanine dye J-aggregates attached to a spherical microcavity. A periodic structure of narrow peaks was observed in the photoluminescence spectrum of the J-aggregates, arising from the coupling between the emission of J-aggregates and the whispering gallery modes (WGMs) of the microcavity. The most striking result of our study is the observation of polarization sensitive mode damping caused by re-absorption of J-aggregate emission. This effect manifests itself in dominating emission from TM modes in the spectral region of J-aggregates absorption band where the TE modes are strongly suppressed. In contrast, the TE modes totally dominate emission spectrum in the region where absorption is negligible. We also demonstrate that the emission intensity can be further enhanced by depositing a hybrid layer of J-aggregates and Ag nanoparticles onto the spherical microcavity. Owing to the concerted action of WGMs and plasmonic hot spots in the Ag aggregates, we observe an enhanced Raman signal from the J-aggregates. Microcavities covered by J-aggregates and plasmonic nanoparticles could be thus useful for a variety of photonic applications in basic science and technology.