Polarization Möbius strip at the tight focus of a generalized Poincaré beam by V.V. Kotlyar, A.A. Kovalev, A.M. Telegin

“…We demonstrate both theoretically and numerically that the initial beam has topological charge –1/2 and, in the center of the focal plane, there is a C-point (a point with circular polarization which makes a C-line along the optical axis) with the singularity index of –1/2 (star), whereas the vector of major axis of the polarization ellipse makes along a certain-radius circle around the optical axis a single-side polarization Möbius stripe of the order –3/2, which has three half-turnovers and one stitching, where two opposite major axis vectors of the polarization ellipse meet.…”
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Azimuthal asymmetries in lepton and heavy-quark pair production in UPCs by Daniël Boer, Luca Maxia, Cristian Pisano

“…In particular, this leads to a feed-in mechanism among harmonics of different orders, which in principle generates harmonics of all (even) orders. …”
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