Helmholtz, Hermann; Fripp, Henry Edward (Julio de 1876). «On the Limits of the Optical Capacity of the Microscope». The Monthly Microscopical Journal16 (1): 15-39. doi:10.1111/j.1365-2818.1876.tb05606.x.
Hell, S. W.; Wichmann, J. (1994). «Breaking the diffraction resolution limit by stimulated emission: Stimulated-emission-depletion fluorescence microscopy». Optics Letters19 (11): 780-782. Bibcode:1994OptL...19..780H. PMID19844443. doi:10.1364/OL.19.000780.