Polarization control in a crossed undulator without a monochromator

In this study, it was demonstrated that the polarization control of light from a crossed undulator can be achieved using material response, without any prior monochromatization. Nonmonochromatized horizontally and vertically polarized radiation emitted from two undulators is irradiated to He atoms, and Rydberg states in the extreme ultraviolet region are excited resonantly. The polarization of the photoexcitation is adjustable in a controlled manner by tuning the electron beam orbit between the two undulators, which is verified by observing Zeeman quantum beats in the fluorescence decays of the He Rydberg states.