Optical Stark Effects in J-Aggregate/Metal Hybrid Nanostructures Exhibiting a Strong Exciton-Surface Plasmon Polariton Interaction

Parinda Vasa Institut für Physik, Carl von Ossietzky Universität, Oldenburg, Germany Department of Physics, Indian Institute of Technology Bombay, Mumbai, India Wei Wang Institut für Physik, Carl von Ossietzky Universität, Oldenburg, Germany Robert Pomraenke Institut für Physik, Carl von Ossietzky Universität, Oldenburg, Germany Margherita Maiuri IFN-CNR, Dipartimento di Fisica, Politecnico di Milano, Milan, Italy Cristian Manzoni IFN-CNR, Dipartimento di Fisica, Politecnico di Milano, Milan, Italy Giulio Cerullo IFN-CNR, Dipartimento di Fisica, Politecnico di Milano, Milan, Italy Christoph Lienau Institut für Physik, Carl von Ossietzky Universität, Oldenburg, Germany

The optical Stark effect (OSE) is a fundamental, coherent nonlinear interaction involving transient shifts of energy levels in the presence of a non-resonant light field [1]. Being a coherent interaction, it is promising for implementing quantum information processing [2]. Its study can also provide important insights into the quantum dynamics of optical excitations. Because of their large optical dipole moment, molecular aggregates serve as prototypes for exploring dipolar coupling between excitons (Xs) and surface plasmon polaritons (SPPs). Strong X-SPP coupling and the formation of hybrid polariton modes has now been demonstrated [3-6], and normal mode splitting up to∼700 meV has been achieved [3]. This makes them attractive for implementing active-photonic functionalities like ultrafast optical switching [4-6], signal processing, and lasing at the nanoscale. Off-resonant, coherent control of the coupled X-SPP modes by the OSE might also provide fundamental insight into the quantum dynamics of hybrid systems.

Differential reflectivity maps of hybrid nanostructures showing OSE

Here, we report the first experimental observation of OSEs in J-aggregate/metal hybrid nanostructures [4-6], exhibiting strong X-SPP coupling. We have recorded differential reflectivity spectra [Fig. (a) and (b)] for hybrid nanostructures comprising gold nano-groove arrays coated with typically 50 nm thick layer of J-aggregated dye. For hybrid systems with moderate normal mode splitting, we observe the expected transient light-induced dressing [6], of the polaritons [Fig. (a)]. For larger normal mode splitting, however, the pump-induced coherent exciton population transiently reduces the X-SPP coupling [4-6], resulting in a sign reversal and significant enhancement of the OSE [Fig. (b)]. Such a coherent all-optical nonlinearity may be interesting for implementing all-optical switching.

References:

[1] R. Mollow, Phys. Rev. A 5, 2217 (1972).

[2] B. Buckley et. al., Science 330, 1212 (2010).

[3] T. Schwartz et. al, Phys. Rev. Lett. 106, 196405 (2011).

[4] P. Vasa, et. al, ACS Nano 4, 7559 (2010).

[5] P. Vasa, et. al, Nat. Photonics 7, 128 (2013).

[6] P. Vasa et. al, Phys. Rev. Lett. (in press).

parinda@iitb.ac.in