Proceedings of the 9th International Conference on X-Ray Absorption Fine Structure

J. Phys. IV France 7 (1997) C2-309-C2-313
DOI: 10.1051/jp4/1997207

Phase Plate Polarimetry with Helical Undulator Sources

L. Varga¹, C. Giles², C. Neumann³, A. Rogalev⁴, C. Malgrange¹, J. Goulon³ and F. de Bergevin<sup>5

1</sup>  Laboratoire de Minéralogie-Cristallographie associé au CNRS, Universités de Paris 6 et Paris 7, Case 115, 4 place Jussieu, 75252 Paris cedex 05, France
²  LNLS C.P. 6192 13081, Campinas, S.P., Brazil
³  ESRF, BP 220, 38043 Grenoble cedex, France
⁴  ESRF, BP 220, 38043 Grenoble cedex France
⁵  Laboratoire de Cristallographie, BP. 166, 38042 Grenoble, France

Abstract
A quarter wave plate made of a 16 μm thin silicon single crystal was inserted in front of a double crystal monochromator which was used as linear polarimeter for Bragg angles close to 45°. This allowed us to demonstrate that, at 2.836 keV, the circular polarisation rate P3 of the helical undulator Helios-I was ≥ 97%. At higher energies, we used a more conventional optical configuration which included again the double crystal monochromator, a diamond quarter-wave plate and a linear polarimeter consisting of a kapton foil scattering at 90°. Fairly reasonable circular polarisation rates were then measured at 7 keV with the second (P₃ ≥ 0.88) and third harmonics (P₃ ≥ 0.84) of the helical undulator Helios-II. On changing the phase of the helical undulator we also measured reasonably good linear polarisation rates (P₂ ≥ 0.94) with the polarisation vector inclined at 45° with respect to the vertical axis. The results obtained with Helios-II call nevertheless for further investigation of possible sources of depolarisation.

© EDP Sciences 1997