Strong coupling of organic molecules to a plasmonic nano-antenna cavity

The optical properties of molecules can be changed by the presence of a cavity. If the cavity is resonant with a certain transition of the molecules, the molecules couple with the cavity. The coupling is characterized by the coupling strength g, which represents the rate of energy exchange. When g is high enough, the exchange rate can overcome the losses of the cavity and the molecules and so-called strong coupling is achieved. The strongly coupled system has new states that can no longer be described by the properties of the 2 components alone. Achieving strong coupling is the goal of this thesis. Plasmonic nanocavities, or nanoantennas can confine light to volumes smaller than the diffraction limit. Rod antennas and dimer antennas, which consists of 2 rod antennas separated by a gap are of interest in this thesis. An interesting property of a dimer is that it can build up a high field strength in the gap, leading to an increase in g. The mode volume is pushed down to an estimated 20 000 nm3, well below the diffraction limit. The length and gap size of the dimers is varied so the plasmonic resonance frequency matches the molecular resonance frequency. This process is backed up with FDTD simulations. The observed coupling strength g for rods is 0.106 ± 0.017 eV and 0.116 ± 0.014 eV for dimers with a molecular concentration of 195 ± 48 mM