Photon sources and instrumentation Figure 1. (a) The scheme for generating EUV FEL radiation with spatially varying polarisation by combining two orthogonally polarised pulses with different transverse modes. (b) Isolation of the Poincaré beam with a filter and detection of the pulse using two CCD cameras that image the intensity of the radiation before and after reflection off a polariser. (c) The intensity after the polariser as the phase between the last two undulators is scanned. (d) Measured Poincaré polarisation distribution superimposed on the intensity profile. (e) The polarisation distribution mapped to the Poincaré sphere shows broad coverage. J. Morgan1, P.R. Ribič2, F. Capotondi2, A. Brynes2, M. Manfredda2, G. De Ninno2,3, L. Novinec2, M. Pancaldi2,4, E. Pedersoli2, A. Simoncig2, C. Spezzani2, M. Zangrando2,5, E. Hemsing1 1 SLAC National Accelerator Laboratory, Menlo Park, CA, USA ² Elettra - Sincrotrone Trieste S.C.p.A., Trieste, Italy ³ University of Nova Gorica, 5000 Nova Gorica, Slovenia ⁴ Department of Molecular Sciences and Nanosystems, Ca’ Foscari University of Venice, Venezia, Italy ⁵ CNR – Istituto Officina dei Materiali (IOM), Trieste, Italy e-mail: jmorgan@slac.stanford.edu Acknowledgments This work was supported by U.S. Department of Energy Contract 218 No. DE-AC02-76SF00515 and Award No. 2021-SLAC-100732. Original paper J. Morgan et al., Nat. Photon. (2025). DOI: 10.1038/s41566-025-01737-7. Fig. 1 (b) (c) (e) (a) (d) Elettra Highlights 2024–2025 151
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