Stimulated emission depletion (STED) is the key optical technology enabling super-resolution microscopy below the diffraction limit. Here, we demonstrate that modulation of STED in the time domain, combined with properly designed lock-in detection, can radically enhance the contrast of fluorescent images of strongly autofluorescent biotissues. In our experiments, the temporally modulated STED technique, implemented with low-intensity continuous-wave laser sources, is shown to provide an efficient all-optical suppression of a broadband fluorescent background, allowing the contrast of fluorescent images of mammal brain tissues tagged with nitrogen-vacancy diamond to be increased by five orders of magnitude.
Amitonova, L., Fedotov, I. V., & Zheltikov, A. M. (2015). Ultrahigh-contrast imaging by temporally modulated stimulated emission depletion. Optics letters, 40(5), 725-728. https://doi.org/10.1364/OL.40.000725