INSTRUMENTATION DEVELOPMENTS FOR X-RAY LINEAR AND CIRCULAR-DICHROISM AT THE ESRF BEAMLINE ID12A

This paper reports on the performance of the instrumentation developed for the ESRF beamline ID12A, which is dedicated to spectroscopic appl ications requiring full control of the polarization at energies greate r than or equal to 2.0 keV. Emphasis is placed on the characterization of various optical components of the beamline and on problems associa ted with either the control or the conversion of the polarization stat e. A few examples have been selected to illustrate what sort of new sp ectroscopic information has already been obtained at the beamline. The se include the comparison of X-ray magnetic dichroism spectra recorded with linear or circular polarization and the very first detection of X-ray natural circular dichroism in single crystals known to exhibit a very large non-linear susceptibility at optical wavelengths.