Radial cavity mode excitation in fluorescent core-shell microcavities

In this letter the authors show that the optical mode spectrum of fluorescent dielectric microparticles can be entirely altered by coating the particles with a semitransparent gold layer. While the particles show the frequently observed whispering gallery mode (WGM) excitations without the metal shell, WGMs are suppressed after the coating procedure. Instead, the observed mode spectra can be explained by the evolution of radial modes, which the authors refer to as "spherical Fabry-Pérot modes" in analogy to the mode patterns observed in planar Fabry-Pérot interferometers.