X-ray natural circular dichroism and chiral-EXAFS in gyrotropic crystals

X-ray natural circular dichroism (XNCD) has been recently detected in the X ANES region for uniaxial and biaxial gyrotropic crystals. Chiral-EXAFS (chi -EXAFS) spectra are reported for the first time over a wider energy range a nd are analysed in terms of multiple-scattering paths of relevant symmetry. For such heavily absorbing single crystals as lithium iodate, paratellurit e or potassium titanyl phosphate, the differential absorption between left- handed and right-handed circularly polarized X-ray photons cannot be measur ed in transmission but gyrotropy effects can still be detected in fluoresce nce excitation spectra. Whereas XNCD and fluorescence-detected X-ray natura l circular dichroism spectra are strictly identical for uniaxial crystals, it has been established that this was true only to the first order for biax ial crystals such as potassium titanyl phosphate.