High resolution multilayer x-ray optics

Presently there is a gap in energy resolution DeltaE/E between a few percent for multilayer x-ray optics and a few 10(-4) for perfect crystal optics (1). One approach to bridge this gap is the development of high-resolution multilayers. We will report on recent advances in this field and discuss both the capabilities and the limitations of this solution. The deposition of hundreds of layers of hard materials is a considerable challenge for the coating system, and stability issues have to be considered with particular care. We have shown theoretically and experimentally that this challenge can be met with a combination of Al(2)O(3) and B(4)C. With 680 bilayers we reached a spectral resolution < 0.3% and a peak reflectivity of almost 50% for 12 keV x-rays. The disagreement with the diffraction properties of a perfect multilayer system could be accurately described by instabilities during the deposition process. With improved stability, such systems can provide still better performances.