Investigation of electronic anisotropies with high purity X-ray polarimetry

The goal of this proposal is the investigation of tiny electronic anisotropies of d and f orbitals in a rare earth cubic compound revealed by polarization analysis of electric quadrupole transitions and dipole-octupole interference at the rare earth L1 edge. We want to detect polarization changes near the L1 absorption edge with a highly sensitive X-ray polarimeter consisting of two polarizer channel-cuts in a crossed setting that is capable to achieve a very high polarization purity up to 10E-10. This technique allows nearly background free measurements of weak electronic anisotropies. It also enables the separation of the two polarization changing effects - X-ray dichroism and X-ray birefringence, whose relative contribution in the X-ray range has hardly been studied. We will investigate at the Gd L1 absorption edge (8376 eV) a model compound with cubic structure, Gd3Ga5O12(GGG), on which several interesting spectroscopic effects have already been discovered.