Optical Chirality in a Strong Coupling System with Surface Plasmons Polaritons and Chiral Emitters

Strong coupling system with plasmons and emitters is an attractive field in the light-matter interaction for the hybrid states combined with the properties of plasmons and emitters. When the emitter are chiral molecules, surface plasmon polaritons (SPPs) provide an excellent research platform which possesses the advantages of chiral field enhancement and electromagnetic wave transmission in the subwavelength size and the chiral strong coupling system has wide applications in optical logic device and biological detection in nanoscale. We experimentally investigate the circular dichroism (CD) of the system with SPPs and chiral J-aggregates from the weak coupling regime to the strong coupling regime. The Rabi splitting of 143.3/154.5 meV, which is a significant phenomenon of the strong coupling can be observed both in the CD and the extinctions. Further experimental results show that, in the strong coupling regime, when the system achieves resonance, the intensity of CD signals corresponding to the upper energy band is stronger than that of the lower energy band, different from the behavior in the extinctions. We develop a method to calculate the dispersion relation in the chiral strong coupling system and explain the extinctions as well as the optical chirality of the hybrid states. The investigation of the CD enriches the characters of hybrid states in the strong coupling system and brings potential applications.