Illustration of the Romanian-German physicist Stefan Hell (born 1962). Hell is best known for his developments in super-resolution fluorescence microscopy. The resolution of optical microscopes is limited to about half the length of the shortest wavelength of visible light (400 nanometres). He invented stimulated emission depletion (STED) microscopy, where fluorescent molecules are attached to cellular structures and have their fluorescence turned on or off by laser beams passing over the specimen. This allows an image to be built up at high resolution even in living tissue. Hell was awarded a share of the 2014 Nobel Prize in Chemistry for this work, along with Eric Betzig and William E. Moerner.