First operation of circular dichroism measurements with periodic photon-helicity switching by a variably polarizing undulator at BL23SU at SPring-8

This article presents the first operation of the magnetic circular dichrois m (MCD) measurement system with periodic photon-helicity switching. The mea surements were performed at the newly constructed soft x-ray beamline-BL23S U- at the third-generation synchrotron radiation facility, SPring-8. The mo nochromator control system was synchronized to the movement of the magnetic row (phase shift) of an APPLE-2 (Sasaki) type variably polarizing undulato r. The periodic phase shift of the undulator provided the switching of heli city polarizing soft x rays up to 0.1 Hz. The closed-orbit distortion of th e storage ring was controlled to avoid optical axis disturbances at this be amline as well as at other beamlines. The circular dichroism spectra with h elicity switching by APPLE-2 show the possibility of high-sensitivity MCD m easurements. This method promotes precise MCD measurements and can be a pow erful technique to study magnetism as well as dichroism. (C) 2001 American Institute of Physics.