Spatial Coherence Properties of Organic Molecules Coupled to Plasmonic Surface Lattice Resonances in the Weak and Strong Coupling Regimes

Tommi Hakala COMP Centre of Excellence, Department of Applied Physics, Aalto University, Espoo, Finland Rekola Heikki Tapani COMP Centre of Excellence, Department of Applied Physics, Aalto University, Espoo, Finland Lei Shi COMP Centre of Excellence, Department of Applied Physics, Aalto University, Espoo, Finland Jani-Petri Martikainen COMP Centre of Excellence, Department of Applied Physics, Aalto University, Espoo, Finland Robert Jan Moerland COMP Centre of Excellence, Department of Applied Physics, Aalto University, Espoo, Finland Department of Imaging Physics, Faculty of Applied Sciences, Delft University of Technology, Delft, Netherlands Päivi Törmä COMP Centre of Excellence, Department of Applied Physics, Aalto University, Espoo, Finland

We study the spatial coherence properties of a system composed of periodic silver nanoparticle arrays covered with fluorescent organic molecule film [1]. The evolution of spatial coherence of this composite structure is investigated both in weak and strong coupling regimes by systematically varying the coupling strength between the localized molecular excitons and the collective, delocalized modes of the nanoparticle array known as surface lattice resonances (SLRs). We show that the high degree of spatial coherence is maintained in the strong coupling regime, even when the mode is very exciton-like (80 %). This is in stark contrast to pure localized excitons, which do not display long range coherence. By appropriately tuning the nanoparticle size, their spacing and the dye molecule concentration, we demonstrate that the hybrid mode properties, such as the dispersion, spatial coherence length and the relative weights of the exciton-SLR superposition, can be tailored with high precision.

[1] Spatial Coherence Properties of Organic Molecules Coupled to Plasmonic Surface Lattice Resonances in the Weak and Strong Coupling Regimes, L. Shi, T. K. Hakala, H. T. Rekola, J.-P. Martikainen, R. J. Moerland, and P. Törmä, Phys. Rev. Lett. 112, 153002, 2014. DOI: http://dx.doi.org/10.1103/PhysRevLett.112.153002

heikki.rekola@aalto.fi