An X-ray Focusing System Combining a Sagittally-bent Crystal and a Kirkpatrick-Baez System

In the production of x-ray microbeams a trade-off between flux and beam size must often be made, particularly when using a bending magnet synchrotron source since the radiation emitted in the horizontal direction is not collimated. To circumvent this problem we have combined the diffraction from a sagitally-bent crystal with the meridional focusing of a Kirkpatrick-Baez (KB) system composed of two reflective surfaces coated with a platinum layer (1st mirror, vertical deflection) and with a Ni/B4C multilayer (2nd mirror, horizontal deflection). The experiments were performed at the ESRF BM5 beamline, for which the most favorable arrangement consisted of illuminating a KB system located faraway from the source with a horizontally converging or diverging beam produced by a sagittally-bent crystal located closer to the source. The 1st mirror demagnified the vertical dimension of the source whilst the 2nd further decreased the beam in the horizontal direction. Several flux/ spot-size configurations were tested by changing the position of the image of the sagittal crystal. The best (preliminary) results gave a focus of 2.6 μm (vertical) x 6.8 μm (horizontal) and an irradiance gain of 2.6 104. These figures were limited by the aberrations of the sagittally-bent crystal