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| This schematic shows the difference between a Fresnel zone plate, a fractal zone plate and a fractal photon sieve. All the components are diffractive lenses but a Fresnel zone plate consists of a series of periodic concentric circles whereas a fractal zone plate comprises circles following a fractal pattern. In a fractal photon sieve, the continuous transparent circular regions of a zone plate are replaced by a high density of discrete holes. (Credit: Walter Furlan) |
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