The fine alignment of X-ray nano-focusing optics, such as Kirkpatrick-Baez (KB) mirrors, depends strongly on the ability to diagnose the X-ray beam at the focus position. Despite conventional diagnostics techniques (e.g. knife-edge) allowing the measurement of the beam profile with sub-micrometer resolution, they may yield poor accuracy for beams with sizes under 100 nm. With nanometer-resolution phase-recovering techniques like ptychography, information about optical aberrations can be obtained experimentally in the complex-valued wavefront. In this work, we use wave-propagation simulations with Synchrotron Radiation Workshop (SRW) to model the CARNAÚBA beamline at Sirius. The beam phase at the KB mirrors exit pupil is decomposed in terms of Zernike rectangular polynomials. The relevant degrees of freedom (DOF) of the mirrors are scanned, allowing the correlation of the Zernike coefficients with the beam profile at focus. Therefore, the aberrations are classified and quantified for each mirror’s DOF, and alignment tolerances are obtained. We find that each DOF can be described by a unique combination of only three Zernike terms. Additionally, a database with the first 15 Zernike coefficients is created by simulating random alignment states and used to train a simple fully-connected neural network. The neural network was able to determine the alignment states of unknown samples with errors below 3%. The combination of Zernike polynomials and neural networks could potentially lead to single-iteration alignment of KB mirrors using wavefront sensing techniques as a diagnostic tool.
Synchrotron scanning X-ray microscopy has been established as a mature technique, bridging the gap between conventional optical microscopy and high-resolution electron microscopy and, notably, adding advantages like large penetration in bulky samples, dose reduction and spectroscopy. The CARNAÚBA beamline at the 4th generation synchrotron source Sirius-LNLS provides an X-ray nanoprobe for simultaneous multi-analytical and coherent X-ray imaging techniques, with spectroscopic capabilities in the 2.05 to 15 keV energy range. The sample is raster-scanned through the nanoprobe to provide two-dimensional maps, which can then be combined with a rotation for computed tomography. In this contribution, some relevant scientific cases for the Day-1 experiments will be presented, along with original instrument solutions for in situ, in operando, cryogenic and in vivo sample environments.
Side-deflecting cylindrical mirrors with sagittal curvature horizontally deflect and focus the beam in the vertical direction. This optical scheme applied to fourth-generation synchrotron light source beamlines has potential advantages leading to nearly aberration-free focus and variable beam size or focus position. We characterize the surface quality of sagittal cylinders in the low spatial frequency range with the long trace profiler (LTP) and the Fizeau interferometer (FZI). In the standard LTP, the sagittal curvature of the cylindrical mirror causes the reflected laser beam to diverge, which consequently shifts the focus out of the detector plane, turning a reliable measurement impossible. Therefore, a positive cylinder lens is placed at Cat's eye position to recollimate the beam. In this paper, we describe the alignment procedure and dene the required accuracy of each degree of freedom for both the cylinder lens and the cylindrical mirror to be characterized. Measurements with the FZI are limited to optics with small curvatures when measuring with a flat reference. We show that measuring a sagittal cylinder slightly out-of-focus overcomes this limitation. Measurements with the FZI also allow to characterize the deformations caused by clamping forces due to fixation. We compare the measured deformation with Finite Element Analysis (FEA) simulation results. We present measured surface height and slope profiles (LTP and FZI) of cylindrical mirrors for SIRIUS beamlines.
Cylindrical mirrors with sagittal curvature are known for non-ideal focusing due to strong aberrations. However, the small emittance of undulator sources at new upcoming fourth-generation synchrotrons causes the footprint of the beam on a sagittal cylinder to be small enough to permit almost aberration-free focusing. The use of side deflecting sagittal cylinders in the optical design of synchrotron beamlines brings advantages to the beam performance: a) it improves stability, because horizontal plane is less a effected by ground vibrations, b) it keeps the beam height with respect to the floor, c) the beam is less sensitive to slope errors in the sagittal plane. Furthermore, a sagittal cylinder in combination with a meridional cylinder or ellipse allows the change of focal spot size and position. In this work, we present the optical scheme of three beamlines including sagittal cylinders for the fourth-generation synchrotron SIRIUS. In MANACA beamline (protein crystallography) a sagittal cylinder and a meridional ellipse face each other in the horizontal plane. By changing the incidence angle of both mirrors in the same direction beam size at sample can be changed from 10 to 100 μm. In SAGUI beamline (SAXS and XRD) both mirrors face the same direction. Changing the incidence angle in opposite direction enables to change the focus position by tens of meters. In CATERETE beamline (Coherent Diffraction Imaging) the two mirrors face each other to create a highly coherent plane wave with a focal spot of 40 μm. We compare the performance of each beamline with their ideal optics counterpart, using wave propagation simulations (SRW).
The soft X-ray beamline IPE is one of the first phase SIRIUS beamlines at the LNLS, Brazil. Divided into two branches, IPE is designed to perform ambient pressure X-ray photo-electron spectroscopy (AP-XPS) and high resolution resonant inelastic X-ray scattering (RIXS) for samples in operando/environmental conditions inside cells and liquid jets. The aim is to maximize the photon flux in the energy range 200-1400 eV generated by an elliptically polarizing undulator source (EPU) and focus it to a 1 μm vertical spot size at the RIXS station and 10 μm at the AP-XPS station. In order to achieve the required resolving power (40.000 at 930 eV) for RIXS both the dispersion properties of the plane grating monochromator (PGM) and the thermal deformation of the optical elements need special attention. The grating parameters were optimized with the REFLEC code to maximize the efficiency at the required resolution. Thermal deformation of the PGM plane mirror limits the possible range of cff parameters depending of the photon energy used. Hence, resolution of the PGM and thermal deformation effects define the boundary conditions of the optical concept and the simulations of the IPE beamline. We compare simulations performed by geometrical ray-tracing (SHADOW) and wave front propagation (SRW) and show that wave front diffraction effects (apertures, optical surface error profiles) has a small effect on the beam spot size and shape.
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