Reflection on multilayer mirrors beam profile and coherence properties

The main advantage of Bragg reflection from a multilayer mirror as a monochromator for hard X rays, is the higher photon flux density because of the larger spectral bandpass compared with crystal lattice reflection. The main disadvantage lies in the strong modulations of the reflected beam profile. This is a major issue for micro imaging applications, where multilayer based monochromators are frequently employed to deliver high photon flux density. A subject of particular interest is the origin of the beam profile modifications, namely the irregular stripe patterns, induced by the reflection on a multilayer. For multilayer coatings in general it is known that the substrate and its surface quality significantly influence the performance of mirrors, as the coating reproduces to a certain degree the roughness and shape of the substrate. This proceedings article reviews recent experiments that indicate potential options for producing wave front preserving multilayer mirrors, as well as new details on the particular mirrors our group has extensively studied in the pas

The simultaneous measurement of energy and linear polarization of the scattered radiation in resonant inelastic soft x-ray scattering

Resonant Inelastic X-ray Scattering (RIXS) in the soft x-ray range is an element-specific energy-loss spectroscopy used to probe the electronic and magnetic excitations in strongly correlated solids. In the recent years, RIXS has been progressing very quickly in terms of energy resolution and understanding of the experimental results, but the interpretation of spectra could further improve, sometimes decisively, from a full knowledge of the polarization of incident and scattered photons. Here we present the first implementation, in a high resolution RIXS spectrometer used to analyze the scattered radiation, of a device allowing the measurement of the degree of linear polarization. The system, based on a graded W/B4C multilayer mirror installed in proximity of the CCD detector, has been installed on the AXES spectrometer at the ESRF; it has been fully characterized and it has been used for a demonstration experiment at the Cu L3 edge on a high-Tc superconducting cuprate. The loss in efficiency suffered by the spectrometer equipped with this test facility was a factor 17.5. We propose also a more advanced version, suitable for a routine use on the next generation of RIXS spectrometers and with an overall efficiency up to 10%.Comment: 26 pages, 8 figure

Depth-graded multilayers

We present first expérimental results on the fabrication and characterization of depthgraded x-ray multilayers providing a broad and well-defined reflectivity profile. We have designed and deposited irregular multilayer structures providing a practically constant reflectivity of about 20% around the first Bragg-reflection and a bandwidth of about 20% in both incident angle and photon energy. Detailed numerical simulations allow for the détermination of residual errors in the layer stack

Miroir simple-ou multi-couches à courbure variable pour microfocalisation de rayonnement synchrotron X

Une optique X focalisante de grande efficacité a été développée et testée. Elle se compose d'un miroir de petite dimension monté sur un courbeur mécanique à 2-moments de base de pivots flexibles. Les principaux avantages de ce système sont l'accordabilité en énergie, la conservation du flux et la possibilité d'interchanger le miroir. Une procédure de mise en forme du miroir en ligne a été diveloppée pour minimiser la taille de la tache focalisée avec une précision inférieure au microradian. Un exemple de réalisation est présenté, dans lequel des multicouches à gradient latéral ainsi qu'un dépôt simple couche d'iridium ont été utilisés pour couvrir une gamme d'énergie entre 7 keV et 30 keV. Avec un facteur de dégrandissement de 128 (tests effectués sur la ligne BM5 de l'ESRF) des tailles de spot inférieures au micromètre ont été obtenues. Le gain maximal en flux à 20 keV était de 535 (688 à 13 keV)