Boundary Condition Perturbation Theory of Optical Resonances of Deformed Dielectric Spheres

Whispering gallery mode resonators are nowadays very popular for several optical applications, ranging from quantum light sources to extremely sensitive sensors for biological and chemical samples. A key feature for many practical usages is their extremely high optical quality factor (Q-factor). However, even small imperfections may reduce the Q-factor drastically. Depending on both the size of the resonator and the wavelength of light, brute-force numerics might be prohibitive and perturbative approaches need to be established. One suitable approach is the boundary condition perturbation theory originally developed by Lord Rayleigh. In this talk, I discuss how to employ this approach to determine the Q-factor of slightly deformed dielectric spheres. This method permits to solve a more than three-decade old problem in a natural and compelling fashion, by avoiding the traditional pitfalls of dealing with quasi-normal modes.