Geometry-induced fluorescence resonances in small lossy capillaries

We report the first experimental demonstration of cavity-induced resonances that occur without total internal reflection. We obtained these resonances by observing the fluorescence spectrum from the molecules enclosed within a small, lossy capillary of the type used for capillary zone electrophoresis. Even with weak reflections from the capillary inner walls, enough feedback exists to superimpose resonances on the otherwise smooth fluorescence spectrum. These resonances, commonly called morphologydependent resonances or whispering-gallery modes, have typically been observed only in cavities in which total internal reflection is present.