Experimental techniques to characterize the geometry of hollow whispering gallery resonators

The lack of knowledge of the precise geometry of hollow whispering gallery mode (WGM) resonators prevents us from having a theoretical model to analyze the WGMs accurately. Very recently, we applied X-ray imaging combined with focused ion beam milling to obtain detailed information on the geometry of a WGM microbubble resonator and developed a theoretical model for the optical modes that exactly matches the measured geometric parameters. The developed theory can be used for any hollow resonators. It is based on perturbation theory used for SNAP bottle resonators and waveguide theory used for rolled-up bottle resonators.