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.