High-resolution fluorescent microscopy techniques. (Left) Stimulated emission by depletion (STED): Light (green) excites a region of sample. A red-shifted irradiance field (red) depletes the fluorescent (excited) state by stimulated emission, “turning off” the molecules at the edges of the originally illuminated region and sharpening the final fluorescent region (orange). (Middle) Single-molecule localization microscopy: Sequential images of the optima from single molecule fluorescence profiles, which can be determined with much higher precision than their widths, yield a final image of densely labeled sample. (Right) The multitude of spatial frequencies contained in the fluorescence profiles from saturated molecules has a similar (and potentially, greater) effect on increasing the range of observable frequencies as a structured illumination pattern.