Seminars Archive

X-ray monochromator based on refraction in refractive lenses

Abstract
Monochromators for x-rays generally use diffraction for dispersing a polychromatic x-ray beam. Diffracting elements are gratings, crystals or multilayer mirrors which allow for a bandwidth of 10-2~10-5. We have explored the possibility of using the chromaticity of a focusing Planar Refractive Lenses (PRL) as an alternative approach to wide band-pass monochromatisation. The strong energy dependence of the refractive index of the PRL material leads to an analogous energy dependence of the focal length of the lens. Mosaic lens, in comparison with parabolic lens, is characterized with higher aperture because of reduced passive material. This allows achieving higher refracting forces. Eliminating the central part in the lens aperture, in combination with a well-defined pinhole aperture in the image plane, the transmittance of photons of the appropriate energy can be relatively high and photons of deviating energy can b e efficiently suppressed. The energy can be tuned by translat ing the pinhole along the optical axis. In the testing experiments at the ANKA Fluo beamline using the mosaic multi-prism type of CRL combined with pinholes and beam stop, we have achieved an energy resolution of 2.0% at 16 keV. The results will be presented and discussed in a comparison with theoretical simulations.