In 1873, Ernst Abbe discovered that the resolution of focusing (‘far-field’) optical microscopy is limited to d = λ/(2nsinα ) > 200 nm, with nsinα denoting the numerical aperture of the lens and λ the wavelength of light. While the diffraction barrier has prompted the invention of electron, scanning probe, and x-ray microscopy, in the life sciences 80% of all microscopy studies are still performed with lens-based (fluorescence) microscopy. The reason is that the 3D-imaging of the interior of (live) cells requires the use of focused visible light. Hence, besides being a fascinating physics endeavor, the development of a far-field light microscope with nanoscale resolution would facilitate observing the molecular processes of life.
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