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Figure 6
Photoionization scheme used to measure the XFEL polarization. Helium atoms from a pulsed gas jet are photoionized by absorption of a single X-ray photon of linear horizontal polarization and a photoelectron is ejected while the photoion recoils with opposite momentum. The photoion momenta are measured in all directions using COLTRIMS, resulting in the 3D momentum distributions (blue circles) when summed over several thousand events. |