Polarization Measurements of Soft X‐ray Emitted from the Figure‐8 Undulator

A figure‐8 undulator is installed in the soft X‐ray beamline BL27SU at SPring‐8 as insertion device. It provides linearly polarized light whose direction of polarization is horizontal for the integer order harmonic light and vertical for the half‐integer order harmonic light. We have measured the degree of linear polarization of the monochromatic soft X‐ray radiation at the end station of the beamline. Photoelectron spectra of Ne emitted in the horizontal direction are recorded for both horizontal and vertical directions of polarization, for two different settings of the front‐end‐slits. The degrees of linear polarization and the anisotropy parameters and branching ratios of photoelectrons are extracted in a self‐consistent manner, at various photon energies. The resultant values for the degree of linear polarization are interpreted with the help of theoretical calculations.