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An alternate multilayer (AML) grating has been prepared by coating an ion etched lamellar grating with a B_4C/Mo_2C multilayer (ML) having a layer thickness close to the groove depth. Such a structure behaves as a 2D synthetic crystal and can reach very high efficiencies when the Bragg condition is satisfied. This AML coated grating has been characterized at the SOLEIL Metrology and Tests Beamline between 0.7 and 1.7 keV and at the four-crystal monochromator beamline of Physikalisch-Technische Bundesanstalt (PTB) at BESSY II between 1.75 and 3.4 keV. A peak diffraction efficiency of nearly 27% was measured at 2.2 keV. The measured efficiencies are well reproduced by numerical simulations made with the electromagnetic propagation code CARPEM. Such AML gratings, paired with a matched ML mirror, constitute efficient monochromators for intermediate energy photons. They will extend the accessible energy for many applications as x-ray absorption spectroscopy or x-ray magnetic circular dichroism experiments.

The techniques of monochromator optimization are reviewed, and it is shown that until recently only a few of the available parameters were used at the same time. Efficient optimization can be performed numerically. The computation method developed at LURE is explained and an example is given. Extension and development of the method are outlined.

The quality of reconstructed images from in-line holograms can be seriously degraded by the linear superposition of twin images having the same information but different foci. Starting from the reconstructed field at the real image plane, we make use of the uncontaminated information contained in the out-of-focus wave (virtual image) outside the in-focus wave (real image) support, together with a finite-support constraint, to form an iterative procedure for twin-image elimination. This algorithm can reconstruct complex objects, provided that they are not recorded in very near-field conditions. For real objects additional constraints can be imposed, extending the algorithm application to very near-field conditions. The algorithm’s convergence properties are studied in both cases, and some examples are shown.

Les expériences conduites autour d’une source de rayonnement synchrotron nécessitent généralement des faisceaux monochromatiques dont la largeur de bande spectrale est beaucoup plus fine que la largeur naturelle d’émission. La manière de réaliser cette sélection est très dépendante, d’un point de vue technologique, de l’énergie de photon.