Periodic multilayers deposited by Distributed Electron Cyclotron Resonance (DECR) sputtering were studied with synchrotron radiation at the ESRF bending magnet beam line BM5. In situ reflectivity measurements at a photon energy of 20keV have been carried out on these samples during a specific heat treatment. A dedicated furnace has been developed to heat the multilayers under vacuum from room temperature up to 550°C. [Ru/B<sub>4</sub>C]<sub>70</sub> and [W/B<sub>4</sub>C]<sub>40</sub> samples with repetition periods of about 4nm were chosen. Simulations of reflectivity measurements were performed to understand the evolution of layer thicknesses and interface widths. Additional ex-situ reflectivity measurements were done at 8keV before and after the annealing experiments to investigate irreversible effects. We will discuss the heat impact on the layered structure and in which way multilayer optics could be thermally pre-treated before their installation on synchrotron beam lines.
A double-reflection multilayer monochromator is being developed at BM5 in order to fulfill two different functions. As a primary monochromator, it provides higher bandpass and higher photon flux than the Si(111) Bragg crystal monochromator. In combination with the crystal monochromator, it rejects the harmonics and the beam exit can be kept fixed. An additional aim is to preserve the beam coherence. Design issues and performances evaluated on the beamline are presented.
The high resolution, high asymmetric diffractive-refractive x-ray lens was tested at BM5 beamline in ESRF. The lens consists of two Si (111) channel-cut crystals in dispersive arrangement with the angle of asymmetry of 12.7°. The channels have a circular profile with the diameter of 22 mm. The test was performed for the energy of 7.8 - 8.1 keV and the focusing distance of 19 - 20 m. At the place of the focus the beam was squeezed horizontally from 8.8 mm (unfocused beam) to 0.4 mm, i.e. more than 20 times. To get a good reflectivity in such a highly asymmetric diffraction, the cylindrical surface had to be mechanically-chemically polished.
Recent progress in the design and the manufacturing of wide bandpass x-ray multilayers has opened up new possibilities in hard x-ray optics, particularly in astrophysics and synchrotron x-ray applications.
In contrast to previous design based on semi-empirical laws or extensive computer calculation, the recent development of an analytical expression has greatly improved the design of aperiodic multilayer mirrors, allowing to generate any given spectral dependence of the reflectivity. In practice, an approximate differential equation is used to derive an in-depth multilayer composition profile whose reflectivity response approaches the desired one. Based on this asymptotic solution, usually sufficiently close to the final solution, the optimum multilayer composition profile is calculated numerically using a classical downhill algorithm.
We have studied the intrinsic characteristics of depth-graded multilayers using the procedure described above, with an emphasis put on the important case of a flat reflectivity response over a large but limited spectral range. The performance of depth-graded multilayer mirrors manufactured at ESRF and characterized at the BM5 beamline are presented. The necessity to account at the design level for deposition process parameters, such as chemical composition and thickness errors, and for the effective optical constants is highlighted.