DESIGN OF AN X-RAY PHASE-PLATE ANALYZER TO MEASURE THE CIRCULAR-POLARIZATION RATE OF A HELICAL UNDULATOR SOURCE

A quarter-wave plate made of a ca 16 mu m-thick silicon single crystal was used at energies as low as 2.8 keV to convert circularly polarize d photons into linearly polarized photons. Coupled to a linear polarim eter, this quarter-wave plate enabled the characterization of the circ ular polarization rate of the radiation emitted by one of the ESRF hel ical undulators, Helios-I. The measured value (ca 97%) is in good agre ement with theoretical predictions. Special attention was paid to the alignment procedures of all relevant optical components of the beamlin e.