Efficient fluorescence inhibition patterns for RESOLFT microscopy.

By exploiting the saturation of a reversible single photon transition, RESOLFT microscopy is capable of resolving three dimensional structures inside specimen with a resolution that is no longer limited by the wavelength of the light in use. The transition is driven by a spatially varying intensity distribution that features at least one isolated point, line or plane with zero intensity and the resolution achieved depends critically on the field distribution around these zeros. Based on a vectorial analysis of the image formation in a RESOLFT microscope, we develop a method to effectively search for optimal zero intensity point patterns under typical experimental conditions. Using this approach, we derived a spatial intensity distribution that optimizes the focal plane resolution. Moreover, we outline a general strategy that allows optimization of the resolution for a given experimental situation and present solutions for the most common cases in biological imaging.