ON THE REQUIREMENTS TO THE INSTRUMENTATION FOR THE NEW-GENERATION OF THE SYNCHROTRON-RADIATION SOURCES - BERYLLIUM WINDOWS

It was shown that the high spatial and time coherency of the X-ray bea m delivered at the ESRF allows one to observe very weak perturbation o f the wave front, resulting in the phase contrast and undesirable spec kle structure of the beam, that impose special requirements to all ele ments to be installed in the optical path such as beryllium windows, f ilters and mirrors. The contrast from existing beryllium windows at th e ESRF beamlines and specially polished Be foils was experimentally st udied at an energy range from 10 to 20 keV. It was revealed that the u neven surface of the beryllium windows leads to a beam structure with intensity changes up to 50-100%. The theory of the phase contrast imag ing by a transparent object was presented and some theoretical estimat ions were made to formulate the requirements imposed on the roughness of the Be window surface to avoid the unwanted deterioration of the be am spatial coherence.