Eliptical mirror position correction based on caustic analysis

MOGNO is the micro and nano tomography dedicated beamline at Sirius, operating at three specific energies: 21.5, 39.0, and 67.7keV. Its optics is composed by a set of three mirrors (pre-KB + KB set), delivering a 3mrad cone beam, coming from a 100x100nm 2 main source. The pre-KB mirror must be aligned to produce a secondary source of 0.3 x 800.0µm 2, however, such an alignment is challenging, as deviations from it produce adverse effects on the beamline’s main source, enlarging it. Moreover, to evaluate a nanofocus a novel strategy is required. Here, it is proposed to use the fluorescence signal from a thin Au line deposited on a Si substrate scanning in the focus region along the horizontal plane, making it possible to visualize the beam’s caustic. Furthermore, it is possible to evaluate the focus size, via the analysis of the gradient of the caustic along the direction perpendicular to beam propagation. Using the described strategy, it was possible to measure a focus size of 603±103nm and 668 ± 114nm, limited by control issues experienced during measurements.