Optical tweezers assisted coupling of nematic droplets to gold nanoparticle clusters: effect on whispering gallery modes

Abstract

Dye-doped liquid crystal (LC) microdroplets exhibit tunable optical resonances modulated by size, shape, temperature, and external perturbations. When a dye-doped nematic microdroplet is coupled to a gold nanoparticle cluster, near-field interactions enhance local electric fields, boosting fluorescence emission. Optical tweezers serve as a tool for the parking of dye-doped nematic microdroplets on gold nanoparticle clusters, enabling the dynamic coupling and excitation of whispering-gallery modes (WGMs). This configuration resulted in amplified WGMs, with a clearly detectable shift in the spectral position. Resonance mode red shifts confirmed efficient photonic–plasmonic coupling, with up to 7 nm tunability achieved without significant degradation of the Q factor. The magnitude of the tunability depends on the size of the gold nanoparticle cluster. Also, the WGM emission spectrum of the nematic microdroplet can be reversibly tuned by decoupling from the gold nanoparticle cluster.