Westphal, VolkerVolkerWestphalKastrup, LarsLarsKastrupHell, StefanStefanHell2017-09-072017-09-072003https://resolver.sub.uni-goettingen.de/purl?gro-2/1632We demonstrate sub-diffraction lateral resolution of 28 +/- 2 nm in far-field fluorescence microscopy through stimulated emission depletion effected by an amplified laser diode. Measurement of the optical transfer function in the focal plane reveals a 6-fold enlargement of the spatial bandwith over the diffraction limit. The resolution is established by imaging individual fluorescent molecules on a surface. Corresponding to 1/25 of the responsible wavelength, the attained resolution represents a new benchmark in far-field microscopy and underscores the viability of fluorescence nanoscopy with visible light, conventional optics and compact laser systems.enjournal_article10.1007/s00340-003-1280-x0001861791000013144051