Helicity switching of circularly polarized undulator radiation by local orbit bumps

Helicity switching of circularly polarized undulator radiation provides a valuable tool in synchrotron radiation experiments, particularly in the study of circular dichroism. At SPring-8, we have developed a helicity switching system by means of selecting radiation from two helical undulators. Right and left circular photon beams are alternately supplied to the beamline using electron beam orbit bumps. Instead of reversing the magnetic field applied to a sample, helicity switched light was used in magnetic circular dichroism measurements and the measuring time was reduced by 13.