Recently, a technique for calibrating the modulation transfer function (MTF) of a broad variety of metrology instrumentation has been demonstrated. This technique is based on test samples structured as one-dimensional binary pseudo-random (BPR) sequences and two-dimensional BPR arrays (BPRAs). The inherent power spectral density of BPR gratings (sequences) and arrays has a deterministic white-noise-like character that allows direct determination of the MTF with uniform sensitivity over the entire spatial frequency range and field-of-view of an instrument. As such, the BPR samples satisfy the characteristics of a test standard: functionality, ease of specification and fabrication, reproducibility, and low sensitivity to manufacturing error. Here we discuss our recent developments directed to the optimization of the sample design, fabrication, application, and data processing procedures, suitable for thorough characterization of large aperture optical interferometers. Compared with the previous coded-aperture based design, the improved, ‘highly randomized’ BPRA pattern of the new test standard provides better accuracy and reliability of instrument MTF and aberration characterization, and enables operation optimization of large aperture optical interferometers. We describe the pattern generation algorithm and tests to verify the compliance to desired BPRA topography. The data acquisition and analysis procedures for different applications of the technique are also discussed.
N. Loh, Dmitri Starodub, Lukas Lomb, Christina Hampton, Andrew Martin, Raymond Sierra, Anton Barty, Andrew Aquila, Joachim Schulz, Jan Steinbrener, Robert Shoeman, Stephan Kassemeyer, Christoph Bostedt, John Bozek, Sascha Epp, Benjamin Erk, Robert Hartmann, Daniel Rolles, Artem Rudenko, Benedikt Rudek, Lutz Foucar, Nils Kimmel, Georg Weidenspointner, Günther Hauser, Peter Holl, Emanuele Pedersoli, MengNing Liang, Mark Hunter, Lars Gumprecht, Nicola Coppola, Cornelia Wunderer, Heinz Graafsman, Filipe R. N. Maia, Tomas Ekeberg, Max Hantke, Holger Fleckenstein, Helmut Hirsemann, Karol Nass, Thomas White, Herbert Tobias, George Farquar, W. Henry Benner, Stefan Hau-Riege, Christian Reich, Andreas Hartmann, Heike Soltau, Stefano Marchesini, Sasa Bajt, Miriam Barthelmess, Lothar Strueder, Joachim Ullrich, Philip Bucksbaum, Keith Hodgson, Mathias Frank, Ilme Schlichting, Henry Chapman, Michael Bogan
Profiling structured beams produced by X-ray free-electron lasers (FELs) is crucial to both maximizing signal intensity for weakly scattering targets and interpreting their scattering patterns. Earlier ablative imprint studies describe how to infer the X-ray beam profile from the damage that an attenuated beam inflicts on a substrate. However, the beams in-situ profile is not directly accessible with imprint studies because the damage profile could be different from the actual beam profile. On the other hand, although a Shack-Hartmann sensor is capable of in-situ profiling, its lenses may be quickly damaged at the intense focus of hard X-ray FEL beams. We describe a new approach that probes the in-situ morphology of the intense FEL focus. By studying the translations in diffraction patterns from an ensemble of randomly injected sub-micron latex spheres, we were able to determine the non-Gaussian nature of the intense FEL beam at the Linac Coherent Light Source (SLAC National Laboratory) near the FEL focus. We discuss an experimental application of such a beam-profiling technique, and the limitations we need to overcome before it can be widely applied.
We employ a coded aperture pattern in front of a charge couple device (CCD) pixilated detector to image fluorescent xrays (6-25KeV) from samples irradiated with synchrotron radiation. Coded apertures encode the angular direction of xrays, and given a known source plane, allow for a large Numerical Aperture x-ray imaging system. The algorithm to develop the free standing coded aperture pattern of the Non-Two-Holes-Touching (NTHT) was developed. The algorithms to reconstruct the x-ray image from the encoded pattern recorded are developed by means of modeling and confirmed by experiments on standard samples. Spatial resolution and efficiency are determined for the next development stage whereby an energy resolving pixilated CCD will be deployed allowing for elemental imaging.
Andrew Martin, Jakob Andreasson, Andrew Aquila, Saša Bajt, Thomas R. Barends, Miriam Barthelmess, Anton Barty, W. Henry Benner, Christoph Bostedt, John Bozek, Phillip Bucksbaum, Carl Caleman, Nicola Coppola, Daniel DePonte, Tomas Ekeberg, Sascha Epp, Benjamin Erk, George Farquar, Holger Fleckenstein, Lutz Foucar, Matthias Frank, Lars Gumprecht, Christina Hampton, Max Hantke, Andreas Hartmann, Elisabeth Hartmann, Robert Hartmann, Stephan Hau-Riege, Günther Hauser, Peter Holl, André Hoemke, Olof Jönsson, Stephan Kassemeyer, Nils Kimmel, Maya Kiskinova, Faton Krasniqi, Jacek Krzywinski, Mengning Liang, Ne-Te Duane Loh, Lukas Lomb, Filipe R. N. Maia, Stefano Marchesini, Marc Messerschmidt, Karol Nass, Duško Odic, Emanuele Pedersoli, Christian Reich, Daniel Rolles, Benedikt Rudek, Artem Rudenko, Carlo Schmidt, Joachim Schultz, M. Marvin Seibert, Robert Shoeman, Raymond Sierra, Heike Soltau, Dmitri Starodub, Jan Steinbrener, Francesco Stellato, Lothar Strüder, Martin Svenda, Herbert Tobias, Joachim Ullrich, Georg Weidenspointner, Daniel Westphal, Thomas White, Garth Williams, Janos Hajdu, Ilme Schlichting, Michael Bogan, Henry Chapman
Results of coherent diffractive imaging experiments performed with soft X-rays (1-2 keV) at the Linac Coherent
Light Source are presented. Both organic and inorganic nano-sized objects were injected into the XFEL beam
as an aerosol focused with an aerodynamic lens. The high intensity and femtosecond duration of X-ray pulses
produced by the Linac Coherent Light Source allow structural information to be recorded by X-ray diffraction
before the particle is destroyed. Images were formed by using iterative methods to phase single shot diffraction
patterns. Strategies for improving the reconstruction methods have been developed. This technique opens
up exciting opportunities for biological imaging, allowing structure determination without freezing, staining or
crystallization.
When x-rays penetrate soft matter, their phase changes more rapidly than their amplitude. Interference effects
visible with high brightness sources creates higher contrast, edge enhanced images. When the object is piecewise
smooth (made of big blocks of a few components), such higher contrast datasets have a sparse solution. We
apply basis pursuit solvers to improve SNR, remove ring artifacts, reduce the number of views and radiation dose
from phase contrast datasets collected at the Hard X-Ray Micro Tomography Beamline at the Advanced Light
Source. We report a GPU code for the most computationally intensive task, the gridding and inverse gridding
algorithm (non uniform sampled Fourier transform).
The latest development of ultrafast free electron laser makes it now possible to perform single molecule diffraction
imaging. In such an experiment, two-dimensional (2D) diffraction images of randomly oriented molecules of the
same type (single molecules) can be captured within femtosecond exposure time. These images can then be
used to deduce the 3D structure of the molecule. Two of the most challenging problems that must be solved in
order to obtain a high resolution 3D reconstruction are: 1) the determination of the relative orientations of 2D
diffraction images; 2) the retrieval of the phase information of a reconstructed 3D diffraction pattern. In this
paper, we will focus on the first problem and discuss the use of common curve detection techniques to deduce
the relative orientations of 2D diffraction images produced from single-molecule diffraction experiments. Such a
technique is based on the fact that Ewald spheres associated with two diffraction images of the same molecule
intersect along a common curve in the reciprocal space. By detecting these curves on each diffraction image, we
can deduce the relative orientations of diffraction images by solving an eigenvalue problem. When the radius of
the Ewald sphere is sufficiently large relatively to the region of reciprocal space we are interested in, the Ewald
sphere becomes flat near the origin of the reciprocal space, and common curves reduce to common lines. In
this case, the orientation determination problem is similar to the one that arises in single particle cryo-electron
microscopy. The recent work of Singer and Shkolnisky [1] shows that the orientation determination problem
can be solved by computing the largest eigenvalues of a symmetric matrix constructed from the common lines
identified among cryo-EM projection images. In this paper, we will extend their technique to diffraction images
on which common curves can be identified.
The major problem of measurement of a power spectral density (PSD) distribution of surface heights with surface profilometers arises due to the unknown modulation transfer function (MTF) of the instruments, which tends to distort the PSD at higher spatial frequencies. The special mathematical properties of binary pseudo-random patterns make them an ideal basis for developing MTF calibration test surfaces. Two-dimensional binary pseudo-random arrays have been fabricated and used for the MTF calibration of the MicroMapTM-570 interferometric microscope with all available objectives. An investigation into the effects of fabrication imperfections on the quality of the MTF calibration and a procedure for accounting for such imperfections are presented.
The major problem of measurement of a power spectral density (PSD) distribution of the surface heights with surface
profilometers arises due to the unknown Modulation Transfer Function (MTF) of the instruments. The MTF tends to
distort the PSD at higher spatial frequencies. It has been suggested [Proc. SPIE 7077-7, (2007), Opt. Eng. 47 (7),
073602-1-5 (2008)] that the instrumental MTF of a surface profiler can be precisely measured using standard test
surfaces based on binary pseudo-random (BPR) patterns. In the cited work, a one dimensional (1D) realization of the
suggested method based on use of BPR gratings has been demonstrated. Here, we present recent achievements made in
fabricating and using two-dimensional (2D) BPR arrays that allow for a direct 2D calibration of the instrumental MTF.
The 2D BPRAs were used as standard test surfaces for 2D MTF calibration of the MicromapTM-570 interferometric
microscope with all available objectives. The effects of fabrication imperfections on the efficiency of calibration are also
discussed.
Our goal was to prepare an X-ray Fluorescence Holography (XFH) experiment at ESRF, in which the holographic information is approximately 0.3% of the overall isotropic fluorescent radiation. This requires a very pure fluorescent signal and the highest possible count rate. Therefore, we designed a focusing analyzer system with large solid angle acceptance. It consists of a sagittally bent pyrolithic graphite crystals with large solid angle acceptance used in the parafocusing mode for the meridional plane. We successfully applied it to collect a large fraction of isotropically emitted Fe, Ni and Pd K(alpha ) fluorescent photons with the [002] and [006] graphite reflections, respectively. After characterizing the phase space efficiency (angular acceptance, focal spot shape) of a 200 mm long, doubly focusing analyzer, we developed a full circular one (220 mm diameter) to increase the solid angle acceptance to approximately 2 10-2 sr, in view of an XFH experiment on MBE grown thin films. This analyzer can be used more generally at K and L edges for atoms with Z greater than or equal to 20.
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