Free electron laser generation of X-ray Poincaré beams

Morgan, Jenny and Hemsing, Erik and McNeil, Brian W J and Yao, Alison (2020) Free electron laser generation of X-ray Poincaré beams. New Journal of Physics, 22 (July). 072001. ISSN 1367-2630

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    An optics-free method is proposed to generate x-ray radiation with spatially variant states of polarization via an afterburner extension to a free electron laser. Control of the polarization in the transverse plane is obtained through the overlap of different coherent transverse light distributions radiated from a bunched electron beam in two consecutive orthogonally polarised undulators. Different transverse profiles are obtained by emitting at a higher harmonic in one or both of the undulators. This method enables the generation of beams structured in their intensity, phase, and polarization - so-called Poincaré beams - at high powers with tunable wavelengths. Simulations are used to demonstrate the generation of two different classes of light with spatially inhomogeneous polarization - cylindrical vector beams and full Poincaré beams.