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 applications requiring full control of the polarization at energies >/=2.0 keV. Emphasis is placed on the characterization of various optical components of the beamline and on problems associated with either the control or the conversion of the polarization state. A few examples have been selected to illustrate what sort of new spectroscopic information has already been obtained at the beamline. These 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.