Crystal field induced linear dichroism in the 3d X-ray absorption of rare-earths

The splitting of the free ion ground state of rare-earths can be investigated using X-ray absorption spectroscopy with polarized light at the M4,5-edges. The linear polarization of the light, combined with the dipole selection rules, allows to study the ordering and separation of the split levels over an energy range of a few meV, even if 1keV photons with 1eV energy resolution are involved.