Xray wave-front analysis as a tool for linear optimization of position and bending of microfocusing mirrors

Microfocusing with mirrors with the precision required by the small emittance of third generation sources implies using aspherical surfaces. The state of the art polishing technology is not sufficient to meet the submicroradian figures needed, and dynamically bent systems are required. The first approach used at ESRF has been to minimize the difference between the computed shape corresponding to the beamline parameters, and the actual shape of the mirror under the control of the Long Trace Profiler (LTP) in the optical laboratory. This was proven experimentally insufficient to cope with various experimental parameter changes and furthermore with the need to change dynamically the angle of incidence when varying the energy. An In situ Xray analysis was introduced by means of a scanning slit and CCD camera. The system is identified by applying unit displacements to all the actuators and the proper corrections are obtained by inversion of the system interaction matrix. The procedure is controlled under SPEC environment and few iterations are required to get surface errors limited performance. The resolution of the CCD is also used to precisely align very grazing incidence Kirkpatrick-Baez focusing geometry. This set up is in use on several beamlines and experimental results are presented.