The error on the position of the rotation center leads to pitch-dependent discrepancies of the sampling positions on the test mirror. On the experimental side, when the LEEP algorithm or any other stitching algorithm is used where the pitch angle must be adjusted between different x-scans, the rotation center of the pitch needs to be known to a certain extent. The ambiguity in the algorithm was addressed by proposing several regularizations in the data acquisition and the algorithm constraints. A modified LEEP algorithm was proposed for the NSP setup to reconstruct the instrument error of the sample-beam autocollimator. This algorithm can reconstruct not only the mirror slope profile, but also the instrument error of the optical head at the same time. proposed the Linearity Error Elimination Procedure (LEEP) algorithm. To overcome this problem, it is possible to stitch partial slope data recorded by measuring the mirror at different pitch angles. These mirrors can have a total slope range larger than the current measuring range of the LTP/NOM/NSP (10 mrad). To produce a diffraction-limited spot size for low energy (high λ), X-ray mirrors with high numerical aperture are required. A soft X-ray nanoprobe will offer nano-imaging and spectroscopy tools non-destructive capabilities to study advanced materials using Nano ARPES and Nano RIXS experimental techniques. To meet the increasing need of the scientific research, more strongly curved focusing mirrors have been proposed for soft X-ray beamline. The sample beam arm (with the sample beam autocollimator) scans the test mirror surface ( x-scan) with a fixed working distance, while the reference beam arm (with reference beam autocollimator) monitors the carriage wobble. With slightly different configuration, the Nano-accuracy Surface Profiler (NSP) was developed with two separate beam arms. The Long Trace Profiler (LTP) and the Nanometer Optical component measuring Machine (NOM) are two classical optical slope profilers widely used in the light source facilities all over the world. Special dedicated optical metrology systems were developed to characterize such high-precision long rectangular X-ray mirrors. As a type of widely used X-ray optics, X-ray mirrors are required to be fabricated at the sub-100 nrad Root Mean Square (RMS) level for residual slope errors or the sub-nm RMS for residual height errors to preserve the wavefront of the incoming X-ray beam and produce a diffraction limited focal spot. To match the evolution of the light source facilities (synchrotron radiation and free-electron lasers), X-ray optical elements must be at the diffraction limit to deliver the high-quality X-ray beam to the end station for scientific research. With the measurement uncertainty of the pitch rotation center, the multi-pitch NSP measurement can estimate the grazing angle θ and the chief ray location x o with their uncertainties, as well as the slope residuals. Taking a real design of an “extreme” elliptical mirror as a case study, we conduct a Monte Carlo simulation to mimic the measurement and characterization process to analyze the impact of several error sources. As demonstrated by our simulations, a proper tolerance evaluation on the measurement of pitch rotation center is needed to assess the measurement accuracy (systematic error) for these strongly aspherical mirrors using the multi-pitch NSP technique. When measuring “extreme”, highly asymmetrically curved, elliptical mirrors, the calculation of the mirror height profile with iterative reconstruction outperforms the classical “flat assumption” (i.e., assuming that the mirror sag is negligible). By revisiting the theory of the multi-pitch Nano-accuracy Surface Profiler (NSP), we derive the sampling position error on the mirror surface as a function of the mirror height profile and the measurement error of the pitch rotation center. To overcome this problem, it is possible to stitch partial slope data by measuring the mirror at different pitch angles (multi-pitch angles). ![]() ![]() Their total slope range exceeds the measuring range of most angular sensors used for X-ray mirror inspection. These highly asymmetrically curved elliptical cylindrical mirrors with a total slope range >10 mrad are extremely challenging to measure. Soft X-ray off-axis elliptical mirrors bring new challenges for X-ray mirror metrology. 3ALBA Synchrotron Light Source, Cerdanyola del Vallès, Spain.2Synchrotron SOLEIL, L’Orme des Merisiers, Gif-Sur-Yvette, France.1National Synchrotron Light Source II, Brookhaven National Laboratory, Upton, NY, United States.Lei Huang 1*, Tianyi Wang 1, François Polack 2, Josep Nicolas 3, Kashmira Nakhoda 1 and Mourad Idir 1
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