A Fresnel lens

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This #short illustrates how a Fresnel lens works. A Fresnel lens is obtained by taking a usual lens, in this case with one straight and one circular boundary, cutting it into slices, and only keeping the outermost parts of each slice. This allows saving space in the horizontal direction, by keeping similar properties as the original lens. This design is often used in projectors, for instance in lighthouses. The page https://www.parabolixlight.com/fresne... gives more details on their working. • Here the index of refraction inside the lens is equal to 2, and a circular wave is emitted at the center of the circular arc in the middle. With these parameter values, according to the lensmaker's equation (see https://en.wikipedia.org/wiki/Lens#Le... ) the part of the circular wave crossing the middle section of the lens is transformed into a linear one. The other parts are transformed into approximately linear waves, with some delay. The delay is of no importance when the device is used as a projector, as light is emitted continously. The distortions near the upper and lower boundary of the lens would be less important for waves of smaller wavelength. • More optics simulations can be found in the playlist • Optics (refraction, diffraction, and ... • Render time: 4 minutes • Color scheme: Plasma by Nathaniel J. Smith and Stefan van der Walt • https://github.com/BIDS/colormap • https://github.com/yuki-koyama/tinyco... • Music: Daytime TV Theme by Kevin MacLeod is licensed under a Creative Commons Attribution 4.0 licence. https://creativecommons.org/licenses/... • Source: http://incompetech.com/music/royalty-... • Artist: http://incompetech.com/ • See also https://images.math.cnrs.fr/Des-ondes... for more explanations (in French) on a few previous simulations of wave equations. • The simulation solves the wave equation by discretization. The algorithm is adapted from the paper https://hplgit.github.io/fdm-book/doc... • C code: https://github.com/nilsberglund-orlea... • https://www.idpoisson.fr/berglund/sof...

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