Simpler STED setups

This work discusses rugged technical simplifications for STED nanoscopy and methods related to it (RESOLFT). STED is a type of laser scanning microscopy that uses stimulated emission in order to inhibit spontaneous fluorescence from outer parts of the focal spot. This deliberate transient off-switching of fluorophores permits even densely packed fluorescent molecules to be spatially isolated from the rest; and because isolated molecules can be registered sequentially — no matter how close they are — the resolution is increased beyond the diffraction limit. For switching, STED asks for a separate inhibition beam modified in a way that it suppresses fluorescence, but only in the peripheral regions of the focal spot. The requirements of a second beam path and additional means for beam shaping have kept STED from gaining the currency it deserves, although high resolution is in huge demand, generally. Here, it is discussed how contemporary STED setups can be simplified radically; in fact up to a point where it is possible to upgrade existing laser scanning systems with a co-aligned STED-beam, simply by adding an element about the size of an optical thin-film filter. As the apparent need for a separate beam path ceases to exist, STED becomes simpler and more reliable. At the same time, the performance is the same as for a traditional STED-setup