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(A) Exemplary 3D arrangement of focal points at the vertex locations of an icosahedron and (B) its spatial frequency spectrum. (A) and (B) are linked via the (inverse) 3D FT, indicated by FT (or iFT). (C) The spectrum is limited to the Ewald surface of a monochromatic wave with wave number k = 2π/λ and two sources with limited aperture size (opening angle α). (D) The resulting field with a close-up view on a single spot.
