The present state of Kirkpatrick-Baez mirror systems at the ESRF

This paper describes the mechanical design of Kirkpatrick-Baez (KB) mirror systems that have been developed at the ESRF over several years. These very compact and stable though flexible focusing devices for synchrotron x-ray beams are based on bending an initially flat, superpolished plate, which permits to vary the focusing conditions. Nowadays a whole family of mechanical benders exists at the ESRF that allows us to choose the most adapted system according to the properties defined by the experiment such as the energy and energy range, the focusing parameters such as magnification and focusing distance and the substrate coatings, i.e. single-layer mirrors or multilayers. The geometrical characteristics of these KB systems can be chosen in terms of focal distances ranging from 0.1 to 3 m and circular or elliptical bending radii from 20 to 1000m. Mirror substrates such as silicon or pyrex, single-layer or multilayer coatings require different motorisations and deformation systems. The very challenging requirements for mechanical resolution and sensitivity have led to the development of several generations of micro-motors. The ESRF has built a special multi-purpose micropusher that provides the required resolution and linearity, a thrust up to 80 N and finally a good position latching. Issues such as mounting interfaces, stress in the bent mirror and the dynamic bender, local mirror deformation and curvature stability had to be addressed and were solved. The ESRF has developed mirror clamping technologies controlled by mechanical and optical metrologies. The dynamic stability and reproducibility requirements to achieve a spot size variable from sub-micron to tens of microns required by various beamlines necessitate a very high degree of stiffness.