An indirectly stimulated emission depletion method for STED microscopy

In stimulated emission depletion (STED) microscopy, the resolution can be improved by directly depleting electrons from the target excitation state to the ground state at the doughnut area. In the study, an indirectly STED method for STED microscopy was proposed. A dynamic model based on state transition process for STED microscopy with triexciton fluorescence quantum dots was firstly developed. The depletion efficiencies of both direct and indirect ways were then theoretically investigated. Compared with direct depletion of quantum dots from their triexciton state to the ground state, indirect depletion of quantum dots from their biexciton state to the ground state was more efficient for triexciton depletion. This indirect depletion method offers a new route to reduce the depletion laser intensity for STED microscopy in order to achieve a nanometer imaging resolution.