Development of an on-axis-visualization stage to observe and align sample with an x-ray beam

An on-axis-visualization stage for accurate sample alignment respect to X-ray beam has been designed and implemented at the diffraction and absorption/fluorescence stations of the BM25-SpLine synchrotron beamline at the ESRF. It is mostly intended for studies involving heterogeneous samples where the analysis is restricted to a particular area of the sample. The OAV system provides a parallax-free image of the sample. This is accomplished by a front-surface mirror at an angle of 45° degrees to reflect the visible sample image 90° up to a zoom optics and digital colour CCD camera. A pinhole (PH) on the mirror in combination with a second PH 100 mm backward provides an on-axis collimated X-ray beam at image centre. The collimator is aligned to the beam axis by two angular and two translational high-precision motorized motions. The OAV stage is synchronized with the sample positioning stage, by a computer software so that the desired sample region is aligned on the X-ray beam by selecting it on the image produced by the video camera. In this work, a complete description of the on-axis-visualization system will be presented including the experimental determination of the alignment accuracy.