Optical commissioning and automated alignment strategy for the QUATI x-ray absorption spectroscopy beamline at Sirius

Abstract

The QUATI beamline¹ at Sirius, the Brazilian 4th generation synchrotron, is designed for high-resolution x-ray absorption spectroscopy experiments in the 4.5 to 35 keV range. This work presents the results of its optical commissioning, focusing on the alignment of its optical components and the implementation of automated routines to overcome mechanical hardware limitations. To evaluate the beam conditioning, we compared experimental beam profiles with results from ray-tracing² and wave propagation³ simulations. While simulations with ideal mirror surfaces predicted a focal spot of about 14x9µm2 (horizontal x vertical FWHM), the inclusion of measured surface errors adjusted this expectation to 14x51.5µm². Our best alignment of the optical elements achieved a focus of 24.8x42.9µm², validating the significant impact of surface errors on the final beam quality. Additionally, we discuss the operational trade-offs required by a temporarily unavailable second mirror bender actuator, which currently requires the beamline to alternate between optimized energy resolution and a focused mode for micro-spectroscopy. Flux measurements and their deviation from theoretical expectations are also presented. A significant challenge was identified in the double crystal monochromator homing procedure, which introduced recurrent offsets in pitch and roll of the second crystal, threatening the robustness of the fixed-exit beam. To mitigate this, we implemented a successive approximation algorithm to automatically recalibrate the polynomial functions for the second crystal’s degrees of freedom with a custom graphical user interface. This automation ensures that the beam remains centered on the focal position with minimal operator intervention. These results provide critical insights into the sensitivity of high-resolution spectroscopy beamlines to optical surface quality and demonstrate the effectiveness of software-driven automation in ensuring mechanical reproducibility and operational stability.