Observation of Self-Phase-Matched Lossless Radiative Modes in Dielectric Spheres

Abstract

A theoretical investigation of plane-wave electromagnetic scattering in active dielectric spheres predicted the existence of resonances that occur at discrete wavelengths. These resonances may be understood from a phase-matched leaky mode, in which the gain in the dielectric exactly compensates for the radiative loss of a mode. This results in a radiative mode that does not decay in time. Therefore, it is described as a lossless radiative mode. Experiments have been performed to verify the existence of these resonances. Self-phase-matched resonances from pumped active dielectric spheres have been observed. Optical pumping was used to provide the gain, and the threshold of each resonant mode was found to be a function of the dye concentration and the radius of the dielectric sphere.