Dielectric microspheres as optical cavities: thermal spectrum and density of states

Abstract
Many recently observed optical properties of dielectric microspheres arise from the fact that they behave as optical cavities with little leakage. The thermal spectrum and the density of states are evaluated for such cavitites as a first step toward quantizing the electromagnetic field. The density of states is shown to obey an asymptotic sum rule. The formalism resolves the apparent contradiction between dissipation (from leakage) and quantization.