X-ray Grating Research Articles

Investigation into the design and diffraction efficiency of shifted dual transmission grating

In inertial confined fusion (ICF) experiments, the temporal evolution of X-ray spectrum can provide important diagnostic information such as electron temperature and density on laser-plasma interaction. Accurate diagnostic requires a wide range of X-ray spectrum from several hundred eV to kilo eV to be measured with high temporal resolution. For traditional single grating spectrometer coupled with streak cameras, the limited recording length of streak cameras severely restricts measured X-ray spectral range in one laser shot. Here we design a shifted dual transmission grating (SDTG) spectrometer for laser-produced plasma X-ray diagnostics in ICF experiments which can provide wide-range X-ray spectrum measurement from 100 eV to 5 keV with high temporal and spectral resolution. This SDTG spectrometer comprises two X-ray gratings: one with high line density and the other with low line density. The high line density grating is used to measure X-ray spectrum from 1000 eV to 5000 eV and the low line density grating measures X-ray spectrum from 100 eV to 1000 eV respectively. These two kinds of X-ray gratings are arranged in a plane with their centers shifted by a certain distance. A shifted double slit component is designed according to the spatial positions of the two gratings and set in front of the photocathode in the streak camera to ensure that two sets of X-ray spectra by two shifted gratings are projected on the photocathode without overlapping. This novel SDTG-based X-ray spectrometer can take the most of recording panel space, offering a path to realize a high resolution and broad spectral ranges in diagnosing soft X-rays. In this paper, the design method and the technical data of the SDTG-based X-ray spectrometer are given. The SDTG-based X-ray spectrometer is integrated, debugged and used to measure X-ray pulse at SG-III prototype facility located in Laser Fusion Research Center of Chinese Academy of Engineering Physics. The time integral results are captured by the SDTG spectrometer in the ICF fluid RT experiments and time-resolved spectra are recorded in indirect drive implosion experiment. Experimental results show the SDTG-based X-ray spectrometer can capture X-ray spectrum ranging from 0.1 keV to 5 keV, with a spectral resolution of 0.04 nm and a temporal resolution of better than 30 ps. By fully utilizing limited recording length, the SDTG-based X-ray spectrometer can realize a wide range temporal X-ray spectrum measurement with enough spectral resolution and temporal resolution. This SDTG spectrometer is a good temporal X-ray diagnostic tool for ICF experiments and other high energy density physics experiments.

Near-field holography enhanced with antireflection coatings—an improved method for fabricating diffraction gratings

Near-field holography (NFH), with its virtues of precise critical dimensions and high throughput, has a great potential for the realization of soft x-ray diffraction gratings. We show that NFH with reflections reduced by the integration of antireflective coatings (ARCs) simplifies the NFH process relative to that of setups using refractive index liquids. Based on the proposed NFH with ARCs, gold-coated laminar gratings were fabricated using NFH and subsequent ion beam etching. The efficiency angular spectrum shows that the stray light of the gratings is reduced one level of magnitude by the suppression of interface reflections during NFH.

Numerical design of X-ray tabletop Talbot interferometer using polycapillary optics as two-dimensional gratings with high aspect ratio

The polycapillary optics was proposed to be used as two-dimensional X-ray gratings with high aspect ratios for high energy X-rays. The X-ray Talbot interferometer was designed numerically using the polycapillary X-ray gratings and a conventional X-ray source. The simulation showed that it was available to get a high-aspect-ratio pattern of the polycapillary X-ray gratings for higher energies than 60keV. Moreover, this design of polycapillary gratings decreased the requirement for high power of the X-ray source. The polycapillary X-ray gratings had potential applications in X-ray imaging technology for medical fields, industrial nondestructive tests, public security, physical science, chemical analysis, life science, nanoscience biology and energy science.

Characterisation of Anisotropic Fibre Orientation in Composites by Means of X-Ray Grating Interferometry Computed Tomography

In this work carbon fibre-reinforced polymer (CFRP) laminates and short glass fibre- reinforced polymers (sGFRP) were investigated by means of X-ray scatter dark field imaging (SDFI) using Talbot-Lau grating interferometer computed tomography. For the characterisation of the laminate structures of CFRP the anisotropic properties of the small angle scattering signal was used to image fibre bundles running in different directions. SDFI allows the visualisation of the weave pattern structure of a carbon fibre bundle in three dimensions, even if the individual fibres cannot be separated or the absorption contrast between the carbon fibres and the epoxy resin matrix is very low. For the investigated sGFRP samples qualitative information about local fibre anisotropies within a specimen were obtained by SDFI. Due to the complex behaviour of fibre alignment during the injection process a clear interpretation of the SDFI signals was difficult. As a reference method, all samples were scanned by means of high resolution cone beam Computed Tomography (µXCT). For the sGFRP the combination of µXCT and appropriate software tools provides local fibre orientations and allows three-dimensional visualisation by colour coding each extracted fibre.

Extended asymmetric-cut multilayer X-ray gratings.

The fabrication and characterization of a large-area high-dispersion blazed grating for soft X-rays based on an asymmetric-cut multilayer structure is reported. An asymmetric-cut multilayer structure acts as a perfect blazed grating of high efficiency that exhibits a single diffracted order, as described by dynamical diffraction throughout the depth of the layered structure. The maximum number of grating periods created by cutting a multilayer deposited on a flat substrate is equal to the number of layers deposited, which limits the size of the grating. The size limitation was overcome by depositing the multilayer onto a substrate which itself is a coarse blazed grating and then polish it flat to reveal the uniformly spaced layers of the multilayer. The number of deposited layers required is such that the multilayer thickness exceeds the step height of the substrate structure. The method is demonstrated by fabricating a 27,060 line pairs per mm blazed grating (36.95 nm period) that is repeated every 3,200 periods by the 120-μm period substrate structure. This preparation technique also relaxes the requirements on stress control and interface roughness of the multilayer film. The dispersion and efficiency of the grating is demonstrated for soft X-rays of 13.2 nm wavelength.

The remarkable timing properties of a ‘hypersoft’ state in GRO J1655-40

We report the identification and study of an unusual soft state of the black hole low-mass X-ray binary GRO J1655-40, observed during its 2005 outburst by the Rossi X-ray Timing Explorer. Chandra X-ray grating observations have revealed a high mass-outflow accretion disc wind in this state, and we show that the broadband X-ray spectrum is remarkably similar to that observed in the so-called `hypersoft' state of the high mass X-ray binary Cyg X-3, which possesses a strong stellar wind from a Wolf-Rayet secondary. The power-spectral density (PSD) of GRO J1655-40 shows a bending power-law shape, similar to that of canonical soft states albeit with larger fractional rms. However, the characteristic bend-frequency of the PSD is strongly correlated with the X-ray flux, such that the bend-frequency increases by two decades for less than a factor 2 increase in flux. The strong evolution of PSD bend-frequency for very little change in flux or X-ray spectral shape seems to rule out the suppression of high-frequency variability by scattering in the wind as the origin of the PSD bend. Instead, we suggest that the PSD shape is intrinsic to the variability process and may be linked to the evolution of the scale-height in a slim disc. An alternative possibility is that variability is introduced by variable absorption and scattering in the wind. We further argue that the hypersoft state in GRO J1655-40 and Cyg X-3 is associated with accretion close to or above the Eddington limit.

X-ray grating interferometry at photon energies over 180 keV

We report on the implementation and characterization of grating interferometry operating at an x-ray energy of 183 keV. With the possibility to use this technique at high x-ray energies, bigger specimens could be studied in a quantitative way. Also, imaging strongly absorbing specimens will benefit from the advantages of the phase and dark-field signals provided by grating interferometry. However, especially at these high photon energies the performance of the absorption grating becomes a key point on the quality of the system, because the grating lines need to keep their small width of a couple of micrometers and exhibit a greater height of hundreds of micrometers. The performance of high aspect ratio absorption gratings fabricated with different techniques is discussed. Further, a dark-field image of an alkaline multicell battery highlights the potential of high energy x-ray grating based imaging.

Slit-scanning differential x-ray phase-contrast mammography: proof-of-concept experimental studies.

The purpose of this work is to investigate the feasibility of grating-based, differential phase-contrast, full-field digital mammography (FFDM) in terms of the requirements for field-of-view (FOV), mechanical stability, and scan time. A rigid, actuator-free Talbot interferometric unit was designed and integrated into a state-of-the-art x-ray slit-scanning mammography system, namely, the Philips MicroDose L30 FFDM system. A dedicated phase-acquisition and phase retrieval method was developed and implemented that exploits the redundancy of the data acquisition inherent to the slit-scanning approach to image generation of the system. No modifications to the scan arm motion control were implemented. The authors achieve a FOV of 160 × 196 mm consisting of two disjoint areas measuring 77 × 196 mm with a gap of 6 mm between them. Typical scanning times vary between 10 and 15 s and dose levels are lower than typical FFDM doses for conventional scans with identical acquisition parameters due to the presence of the source-grating G0. Only minor to moderate artifacts are observed in the three reconstructed images, indicating that mechanical vibrations induced by other system components do not prevent the use of the platform for phase contrast imaging. To the best of our knowledge, this is the first attempt to integrate x-ray gratings hardware into a clinical mammography unit. The results demonstrate that a scanning differential phase contrast FFDM system that meets the requirements of FOV, stability, scan time, and dose can be build.

An improved phase shift reconstruction algorithm of fringe scanning technique for X-ray microscopy.

The X-ray phase imaging method has been applied to observe soft biological tissues, and it is possible to image the soft tissues by using the benefit of the so-called "Talbot effect" by an X-ray grating. One type of the X-ray phase imaging method was reported by combining an X-ray imaging microscope equipped by a Fresnel zone plate with a phase grating. Using the fringe scanning technique, a high-precision phase shift image could be obtained by displacing the grating step by step and measuring dozens of sample images. The number of the images was selected to reduce the error caused by the non-sinusoidal component of the Talbot self-image at the imaging plane. A larger number suppressed the error more but increased radiation exposure and required higher mechanical stability of equipment. In this paper, we analyze the approximation error of fringe scanning technique for the X-ray microscopy which uses just one grating and proposes an improved algorithm. We compute the approximation error by iteration and substitute that into the process of reconstruction of phase shift. This procedure will suppress the error even with few sample images. The results of simulation experiments show that the precision of phase shift image reconstructed by the proposed algorithm with 4 sample images is almost the same as that reconstructed by the conventional algorithm with 40 sample images. We also have succeeded in the experiment with real data.

Experimental comparison of grating- and propagation-based hard X-ray phase tomography of soft tissue

When imaging soft tissues with hard X-rays, phase contrast is often preferred over conventional attenuation contrast due its superior sensitivity. However, it is unclear which of the numerous phase tomography methods yields the optimized results at given experimental conditions. Therefore, we quantitatively compared the three phase tomography methods implemented at the beamline ID19 of the European Synchrotron Radiation Facility: X-ray grating interferometry (XGI), and propagation-based phase tomography, i.e., single-distance phase retrieval (SDPR) and holotomography (HT), using cancerous tissue from a mouse model and an entire heart of a rat. We show that for both specimens, the spatial resolution derived from the characteristic morphological features is about a factor of two better for HT and SDPR compared to XGI, whereas the XGI data generally exhibit much better contrast-to-noise ratios for the anatomical features. Moreover, XGI excels in fidelity of the density measurements, and is also more robust against low-frequency artifacts than HT, but it might suffer from phase-wrapping artifacts. Thus, we can regard the three phase tomography methods discussed as complementary. The application will decide which spatial and density resolutions are desired, for the imaging task and dose requirements, and, in addition, the applicant must choose between the complexity of the experimental setup and the one of data processing.

Multilayer-coated blazed grating with variable line spacing and a variable blaze angle.

The blazing ability of multilayer-coated blazed gratings (MBGs) was systematically investigated via numerical calculation of the diffraction efficiency with a rigorous electromagnetic simulation code. It was found that the blazing condition is not exact and allows significant deviation from the ideal situation for ultra-dense MBGs. A mismatch of the interfaces of the multilayer (ML) stacks of adjacent grooves results in a modified effective blaze angle, which gives the opportunity to control and tune precisely the blaze angle via a proper choice of ML d-spacing. Also this allows a new kind of x-ray gratings that have a variable line spacing (VLS) as well as a variable blaze angle. Precise adjustment of a local blaze angle of a VLS MBG can be achieved with a laterally graded ML, providing very high diffraction efficiency for the whole area of the grating.

Developments of X-Ray Grating Imaging Technology

The present paper reviews the X-ray grating imaging systems at home and abroad from the aspects of technological characterizations and the newest researching focus. First, not only the imaging principles and the frameworks of the typical X-ray grating imaging system based on Talbot-Lau interferometry method, but also the algorithms of retrieving the signals of attenuation, refraction and small-angle scattering are introduced. Second, the system optimizing methods are discussed, which involves mainly the relaxing the requirement of high positioning resolution and strict circumstances for gratings and designing large field of view with high resolution. Third, two and four-dimensional grating-based X-ray imaging techniques are introduced.

IEEE Access Special Section Editorial: Emerging Computed Tomography Technologies

X-ray computed tomography (CT) has a central role in clinical imaging, often as the first and only imaging study before definitive intervention for a wide variety of conditions. X-ray micro-CT is similarly important in preclinical imaging with anatomically and physiologically relevant small animal models of human diseases. The field of X-ray CT is entering another Spring. Buds are blooming in the areas of X-ray sources such as those based on carbon nanotubes (CNTs) or free-electron lasers; detectors, especially photon-counting modules; X-ray gratings; contrast agents; compressive sensing (CS); and reconstruction methods. Synergistically, these innovations can be integrated to revolutionize the CT field, achieving a quantum leap in performance for biomedical applications.

Grating-based phase contrast tomosynthesis imaging: proof-of-concept experimental studies.

This paper concerns the feasibility of x-ray differential phase contrast (DPC) tomosynthesis imaging using a grating-based DPC benchtop experimental system, which is equipped with a commercial digital flat-panel detector and a medical-grade rotating-anode x-ray tube. An extensive system characterization was performed to quantify its imaging performance. The major components of the benchtop system include a diagnostic x-ray tube with a 1.0 mm nominal focal spot size, a flat-panel detector with 96 μm pixel pitch, a sample stage that rotates within a limited angular span of ± 30°, and a Talbot-Lau interferometer with three x-ray gratings. A total of 21 projection views acquired with 3° increments were used to reconstruct three sets of tomosynthetic image volumes, including the conventional absorption contrast tomosynthesis image volume (AC-tomo) reconstructed using the filtered-backprojection (FBP) algorithm with the ramp kernel, the phase contrast tomosynthesis image volume (PC-tomo) reconstructed using FBP with a Hilbert kernel, and the differential phase contrast tomosynthesis image volume (DPC-tomo) reconstructed using the shift-and-add algorithm. Three inhouse physical phantoms containing tissue-surrogate materials were used to characterize the signal linearity, the signal difference-to-noise ratio (SDNR), the three-dimensional noise power spectrum (3D NPS), and the through-plane artifact spread function (ASF). While DPC-tomo highlights edges and interfaces in the image object, PC-tomo removes the differential nature of the DPC projection data and its pixel values are linearly related to the decrement of the real part of the x-ray refractive index. The SDNR values of polyoxymethylene in water and polystyrene in oil are 1.5 and 1.0, respectively, in AC-tomo, and the values were improved to 3.0 and 2.0, respectively, in PC-tomo. PC-tomo and AC-tomo demonstrate equivalent ASF, but their noise characteristics quantified by the 3D NPS were found to be different due to the difference in the tomosynthesis image reconstruction algorithms. It is feasible to simultaneously generate x-ray differential phase contrast, phase contrast, and absorption contrast tomosynthesis images using a grating-based data acquisition setup. The method shows promise in improving the visibility of several low-density materials and therefore merits further investigation.

Holotomography versus X-ray grating interferometry: A comparative study

X-ray phase-contrast imaging techniques are used at synchrotron facilities to visualize tiny density variations in bulk samples. They overcome the limitations of other non-destructive methods, which often provide insufficient spatial and/or density resolution. Holotomography (HT) and X-ray grating interferometry (XGI) are among the most powerful phase-contrast techniques. Here, we show a direct comparison of HT versus XGI. We find that XGI excels in fidelity of the density measurements and is more robust against low-frequency artifacts, while HT is superior in spatial resolution. This study gives indications for applications and developments of phase-contrast imaging.

X-RAY GRATING OBSERVATIONS OF RECURRENT NOVA T PYXIDIS DURING THE 2011 OUTBURST

The recurrent nova T Pyx was observed with the X-ray gratings of Chandra and XMM-Newton, 210 and 235 days, respectively, after the discovery of the 2011 April 14 outburst. The X-ray spectra show prominent emission lines of C, N, and O, with broadening corresponding to a full width at half maximum of ~2000-3000 km/s, and line ratios consistent with high-density plasma in collisional ionization equilibrium. On day 210 we also measured soft X-ray continuum emission that appears to be consistent with a white dwarf (WD) atmosphere at a temperature ~420,000 K, partially obscured by anisotropic, optically thick ejecta. The X-ray continuum emission is modulated with the photometric and spectroscopic period observed in quiescence. The continuum at day 235 indicated a WD atmosphere at a consistent effective temperature of 25 days earlier, but with a lower flux. The effective temperature indicates a mass of ~1 solar mass. The conclusion of partial WD obscuration is supported by the complex geometry of non-spherically-symmetric ejecta confirmed in recent optical spectra obtained with the Southern African Large Telescope (SALT) in November and December of 2012. These spectra exhibited prominent [O III] nebular lines with velocity structures typical of bipolar ejecta.

Energy resolved X-ray grating interferometry

Although compatible with polychromatic radiation, the sensitivity in X-ray phase contrast imaging with a grating interferometer is strongly dependent on the X-ray spectrum. We used an energy resolving detector to quantitatively investigate the dependency of the noise from the spectral bandwidth and to consequently optimize the system—by selecting the best energy band matching the experimental conditions—with respect to sensitivity maximization and, eventually, dose. Further, since theoretical calculations of the spectrum are usually limited due to non-ideal conditions, an energy resolving detector accurately quantifies the spectral changes induced by the interferometer including flux reduction and beam hardening.

Optimizing and characterizing grating efficiency for a soft X-ray emission spectrometer

The efficiency of soft X-ray diffraction gratings is studied using measurements and calculations based on the differential method with the S-matrix propagation algorithm. New open-source software is introduced for efficiency modelling that accounts for arbitrary groove profiles, such as those based on atomic force microscopy (AFM) measurements; the software also exploits multi-core processors and high-performance computing resources for faster calculations. Insights from these calculations, including a new principle of optimal incidence angle, are used to design a soft X-ray emission spectrometer with high efficiency and high resolution for the REIXS beamline at the Canadian Light Source: a theoretical grating efficiency above 10% and resolving power E/ΔE > 2500 over the energy range from 100 eV to 1000 eV are achieved. The design also exploits an efficiency peak in the third diffraction order to provide a high-resolution mode offering E/ΔE > 14000 at 280 eV, and E/ΔE > 10000 at 710 eV, with theoretical grating efficiencies from 2% to 5%. The manufactured gratings are characterized using AFM measurements of the grooves and diffractometer measurements of the efficiency as a function of wavelength. The measured and theoretical efficiency spectra are compared, and the discrepancies are explained by accounting for real-world effects: groove geometry errors, oxidation and surface roughness. A curve-fitting process is used to invert the calculations to predict grating parameters that match the calculated and measured efficiency spectra; the predicted blaze angles are found to agree closely with the AFM estimates, and a method of characterizing grating parameters that are difficult or impossible to measure directly is suggested.

基于X射线光栅成像的多衬度显微计算层析系统

基于X射线光栅成像的多衬度显微计算层析系统

Cadaveric and in vivo human joint imaging based on differential phase contrast by X-ray Talbot-Lau interferometry

We developed an X-ray phase imaging system based on Talbot-Lau interferometry and studied its feasibility for clinical diagnoses of joint diseases. The system consists of three X-ray gratings, a conventional X-ray tube, an object holder, an X-ray image sensor, and a computer for image processing. The joints of human cadavers and healthy volunteers were imaged, and the results indicated sufficient sensitivity to cartilage, suggesting medical significance.