High-Q whispering gallery modes of doped and coated single microspheres and their effect on radiative rate

Abstract

Fluorescence spectra of two organic dyes doped in polymer beads as well as coated on single microparticles of silica exhibit whispering gallery modes (WGMs). For doped microspheres, theoretical simulations on WGMs have been carried out based on the Lorentz-Mie theory by varying the refractive index and the diameter of the microparticle. Similarly, for a coated microsphere, an Aden and Kerker model of the Lorentz-Mie theory has been used to simulate WGMs. For diameters ⩾8 μm, low-resolution simulations of scattering efficiency fail to show modes of higher-quality factors (Q~108). A new procedure of identifying these modes is given here that does not require use of high-performance computing. Effects of WGMs on decay rates have also been studied. It has been found that, while doped microparticles exhibit no effect on the radiative rate, coated microparticles show inhibition of the decay rate for smaller sizes. Decay rates of single-coated microspheres are found to be distinctly different from those of randomly shaped single microcrystals.