Abstract
Scanning X-ray microscopy such as X-ray ptychography requires accurate and fast positioning of samples in the X-ray beam. Sample stages often have a high mobile mass as they may carry additional mechanics or mirrors for position measurements. The high mobile mass of a piezo stage can introduce vibrations in the setup that will lead to imaging quality deterioration. Sample stages also require a large travel range which results in a slow positioning step response and thus high positioning overhead. Moving lightweight X-ray optics, such as focusing Fresnel zone plates, instead of the sample can improve the situation but it may lead to undesired variations in the illumination probe which may result in reconstruction artifacts. This paper presents a combined approach in which a slow sample stage mechanism covers the long distance range for a large field of view, and a light-weight optics scanner with a small travel range creates a superimposed motion to achieve a fast step response. The step response in the ptychographic tomography instrument used was thereby improved by an order of magnitude, allowing for efficient measurement without loss of imaging quality.
Highlights
In scanning X-ray microscopy, either the sample is shifted through a beam (Shapiro et al, 2014; Menzel et al, 2010) or the X-ray optics are shifted with respect to the sample (Takeichi et al, 2016; Medjoubi et al, 2013; Kilcoyne et al, 2003, 2010; Klug et al, 2018) and different types of signals are recorded, such as the total or diffraction intensity of transmitted light or an X-ray fluorescence signal emitted by the sample (Kaulich et al, 2011; Chen et al, 2014)
The high resonance frequency of the Fresnel zone plates (FZPs) scanner compared with the sample stage leads to a better overall stability of the setup because faster feedback can be applied to the FZP stage compensating for position vibrations in the sample stage
We have developed a new approach for scanning X-ray microscopy by combining a slow sample stage possessing a long travel range with a fast but small range positioner for the beamdefining optics
Summary
In scanning X-ray microscopy, either the sample is shifted through a beam (Shapiro et al, 2014; Menzel et al, 2010) or the X-ray optics are shifted with respect to the sample (Takeichi et al, 2016; Medjoubi et al, 2013; Kilcoyne et al, 2003, 2010; Klug et al, 2018) and different types of signals are recorded, such as the total or diffraction intensity of transmitted light or an X-ray fluorescence signal emitted by the sample (Kaulich et al, 2011; Chen et al, 2014). A small transversal movement of the lens leads to an effective movement of the illumination probe This approach is already used in other ptychography instruments (Celestre et al, 2017; Klug et al, 2018; Vine et al, 2012) to move the lightweight lens instead of the sample stage and reducing the positioning overhead. The resulting metrology of our instrument is a combined system of laser interferometry measuring the sample position with respect to the holding structure of the FZP scanner and the capacitive signal measuring the effective position of the FZP lens. This control mode is not implemented yet, but foreseen in the future
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