Direct measurement of multi-angle evanescent field by whispering gallery mode of the microsphere and fluorescent spots in an optical waveguide fluorescence microscopy

Evanescent field (EF) has been widely applied in various micro-imaging techniques for its ability to excite surfaces. However, measuring the multi-angle EF remains challenging. In this paper, the whispering gallery mode (WGM) is observed in an excited microsphere on an optical waveguide (OWG) with a thickness of 0.6 mm, which is used to determine the diameter of the excited microsphere. A simple and nondestructive measurement method for multi-angle OWG-EF is proposed, which is based on the reliable diameter of the microsphere, determined by WGM and the TIRF spots. The measurement result for multi-angle OWG-EF shows a dynamic range between ∼180 and ∼2400 nm, which shows good agreement with the simulation results. The method synchronization possible for EF measurements and fluorescent experiments.