J. Phys. IV France
Volume 7, Numéro C2, Avril 1997
Proceedings of the 9th International Conference on X-Ray Absorption Fine Structure
Page(s) C2-309 - C2-313
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 Bergevin5

1  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

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