Separation-sensitive measurements of morphology dependent resonances in coupled fluorescent microspheres.

The inelastic emission spectrum of a single fluorescent microsphere (bead) exhibits resonances arising from whispering gallery modes. Two beads in close proximity form a coupled bisphere. Coherent coupling arises from each bead's evanescent field and leads to resonance splitting. Here we collect emission spectra of two coupled beads, with nearly identical diameters, as spacing between beads is varied. Using these size-matched beads allows us to probe resonance splitting under strong coupling conditions.