Effects of polarization on the de-excitation dark focal spot in STED microscopy

The size of the dark focal spot directly determines the resolution and stability of stimulated emission depletion (STED) microscopy. This paper investigates the relationship between the size of the dark focal spot and the polarization of the input light beam. The types of fundamental polarization are discussed, their effects on the dark focal spot are compared and the optimized mode for each kind of polarization is proposed. The results of the analysis provide the theoretical basis and reference for designing a STED system.