Information Loss by Asymmetry and Small Aperture (IMAGE)
Caption
(A) A stone falling in a pond produces full circular waves that are centered on the impact point, and those waves would back propagate onto that same point if time could be reversed. Using this time-reversal argument, if one generates back propagating circular waves from a limited arc, they will not necessarily focus at the center. (B) Representation of how diffraction effects compete with focusing for a beam of different initial size, that is different aperture. Going from left to right on the x-axis, the input beam size (aperture size , orange line) increases. For a large beam, focusing is strong, leading to a small cross section in the focal plane (blue line). If the aperture is reduced, a critical situation is reached (dashed line) where is same as . At the critical point where the two lines cross, focusing and diffraction effects are equal, and energy (red) is best focused between the lens and the initial focal plane, which means that the effective focal plane has shifted towards the lens. Extremely small apertures correspond to a point source and produce diffraction without focusing.
Credit
Institute for Basic Science (IBS)
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