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CiPo - Beamline

Circular Polarization

Measurements of the polarization were made using a multilayer polarimeter at several photon energies between 92 and 573 eV. The measured linear and circular polarization rates as a function of the horizontal deflection parameter (i.e. EEW horizontal current Ih) for wiggler mode are shown in the figures. At 92.5 eV a comparison  between undulator and wiggler mode of operation is reported. In the undulator case a maximum circular polarization rate close to unit can be obtained with equal vertical and horizontal deflection parameters (Kx=Ky), whereas in the wiggler case smaller values of the circular polarization rate are obtained due to the ratio Kx/Ky always less than unit. In both cases reversing the horizontal magnetic field direction results in a change of the helicity of the radiation as expected. The photon energy range below 40 eV is available with the characteristic discrete line spectrum emitted by an undulator.
The degree of circular polarization changes with photon energy in the range from 40% at 8.5 eV to 80% at 575 eV. Full circular polarization condition (90%) is achieved when the EEW works as a pure circular undulator, i.e. when the horizontal and vertical magnetic fields are equal. Under these conditions the available first harmonic lies in the photon energy range between 50 eV and 150 eV.

Last Updated on Wednesday, 13 February 2013 16:18