Super-resolution techniques

As the light is diffracted on the apperture of the objective of an optical microscope, a point-shaped object will not be imaged as a point but as a intensity distribution that can be described by the Point Spread Function (PSF). This has the consequence that two objects whose distance is smaller than a certain value cannot be distinguished any more as their PSF will merge.
This distance or resolution limit can be estimated by the Rayleigh criterion:
where λ is the excaitation wavelength, n the refraction index of the medium and α half of the angle of the aperture of the objective.

Different ways have been found to circumvent this barrier, either by stochastically allowing only one fluorescent emitter being active in a diffraction limited area (STORM/PALM) or by actively modelling the shape of the PSF (STED).

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