STED nanoscopy with wavelengths at the emission maximum.

Commonly, in stimulated emission depletion (STED) fluorescence nanoscopy, light of a wavelength located at the red tail of the emission spectrum of the dye is used to shrink the effective fluorophore excitation volume and thus to obtain images with sub diffraction resolution. Here, we demonstrate that continuous wave (CW) STED nanoscopy is feasible using STED wavelengths located at the emission maximum, where the cross section for stimulated emission is up to 10-fold larger than at the red tail. As a result, STED imaging becomes possible at equally lower STED beam power. Besides, fluorophores that have been considered inapplicable in certain wavelength constellations are thus becoming usable