The UE49 undulator at the storage ring BESSY II is an elliptical polarizing insertion device of the APPLE-type. The difference to a standard planar undulator is the horizontally separated magnet rows. The shifting of these rows produces a helical field at the position of the electron beam causing an elliptical or even circular trajectory. Consequently, elliptically or circularly polarized radiation is emitted.
Additionally, the UE49 undulators can be operated in the antiparallel mode for the production of linearly polarized light with arbitrary angles.
Fig. 2: Accessible photon energies for the parallel mode as function of gap and shift.
Fig. 3: Accessible photon energies for antiparallel mode as function of gap and shift.
Fig. 4: Accessible energies as function of the angle of the linear polarization for antiparallel mode. The energy region between 520eV and 600eV can not be reached for all angles (see the energy gap between 1.Harmonic max. and 3. Harmonic Min)!