Talbot Interferometer Research Articles

Small-angle scattering computed tomography (SAS-CT) using a Talbot-Lau interferometer and a rotating anode x-ray tube: theory and experiments

X-ray differential phase contrast imaging methods, including projection imaging and the corresponding computed tomography (CT), have been implemented using a Talbot interferometer and either a synchrotron beam line or a low brilliance x-ray source generated by a stationary-anode x-ray tube. From small-angle scattering events which occur as an x-ray propagates through a medium, a signal intensity loss can be recorded and analyzed for an understanding of the micro-structures in an image object. This has been demonstrated using a Talbot-Lau interferometer and a stationary-anode x-ray tube. In this paper, theoretical principles and an experimental implementation of the corresponding CT imaging method are presented. First, a line integral is derived from analyzing the cross section of the small-angle scattering events. This method is referred to as small-angle scattering computed tomography (SAS-CT). Next, a Talbot-Lau interferometer and a rotating-anode x-ray tube were used to implement SAS-CT. A physical phantom and human breast tissue sample were used to demonstrate the reconstructed SAS-CT image volumes.

Fabrication of high precision X-ray mask for X-ray grating of X-ray Talbot interferometer

X-ray imaging is used in many applications such as medical diagnosis and non-destructive inspection, and has become an essential technologies in these areas. In one image technique, X-ray phase information is obtained using X-ray Talbot interferometer, for which X-ray diffraction gratings are required; however, the manufacture of fine, highly accurate, and high aspect ratio gratings is very difficult. X-ray lithography could be used to fabricate structures with high precision since it uses highly directive syncrotron radiation. Therefore, we decided to fabricate X-ray gratings using X-ray lithography technique. The accuracy of the fabricated structure depends largely on the accuracy of the X-ray mask used. In our research, we combined deep silicon dry etching technology with ultraviolet lithography in order to fabricate untapered and high precision X-ray masks containing rectangular patterns. We succeeded in fabricating an X-ray mask with a pitch of 5.3 μm. The thickness of the Au absorber was about 5 μm, and the effective area was 60 × 60 mm2, which is a sufficient size for phase tomography imaging. We demonstrated the utility of the Si dry etching process for making high precision X-ray masks.

Analysis of polychromaticity effects in X-ray Talbot interferometer

The influence of polychromaticity of the X-ray source on the performance of an X-ray Talbot interferometer applied for phase-contrast imaging is analyzed through numerical simulations based on the Fresnel diffraction theory. The presented simulation results show that the visibility of the self-image is fairly insensitive to the source polychromaticity and explain why the interferometer could be well combined with polychromatic X-ray sources in recent experiments. Furthermore, the self-image with a high visibility can be obtained under polychromatic illumination even at a high-order fractional Talbot distance. This fact implies that the acquired image quality for phase measurements can be improved, since the primary signal for phase measurement is proportional to the inter-grating distance. Finally, we mention that the results are also valid for Talbot-Lau interferometer and scanning double-grating configuration.

Quantitative coherence analysis with an X-ray Talbot–Lau interferometer

Differential phase-contrast (DPC) X-ray imaging has been performed in the Talbot-Lau configuration, in which the X-ray source was a combination of an absorption grating and a laboratory X-ray generator. We report here quantitative analysis of partial coherence effects on the X-ray Talbot-Lau interferometer. Based on the visibility of the self-image, the well-known geometry condition is reproduced. It is shown that effects of partial coherence are determined by the opening ratio of the source grating, and that the effects are independent of the Talbot order and the type of the phase grating, a condition quite different from those in a Talbot interferometer. A possible explanation is discussed from the point of view of the effective spatial coherence length. Taking into account the available X-ray flux and experimental fluctuations, we present the optimum opening ratio. Furthermore, we mention that our results can also be successfully used to discuss the properties of a multiline X-ray source.

Fabrication of X-rays mask with carbon membrane for diffraction gratings

We have produced diffraction gratings for obtaining high resolution X-ray phase imaging, such as X-ray Talbot interferometer. These diffraction gratings were required to have a fine, high accuracy, high aspect ratio structure. Therefore, we decided to use the X-rays lithography technique that used synchrotron radiation of the directivity for a manufacture process. The accuracy of the completed structure depends largely on the accuracy of the X-ray mask. In our group, a resin material is conventionally used for the membrane of large X-ray masks. However, X-ray masks comprising a resin membrane have the disadvantage that, after several cycles of X-ray exposure, they crease and sag due to X-ray-derived heat. As a substitute for the conventional resin membrane, we experimentally fabricated a new X-ray mask using a carbon wafer membrane. The newly fabricated X-ray mask was subjected to X-ray exposure experiment. We succeeded in making the structure body which was almost shape. And the experimental results verified that the new mask did not deteriorate even when used repeatedly, demonstrating that it was highly durable.

Real-time slope mapping and defect detection in bent plates using Talbot interferometry

We demonstrate a simple method for obtaining slope contours of bent plates using Talbot interferometry. The technique has been used to map slope contours of polymethyl methacrylate specimens of different shapes. The Talbot image of a coarse grating is projected onto a specimen such that the self-image is backreflected onto the same grating again. As a Talbot interferometer is basically a grating shearing interferometer, it results in the generation of characteristic slope maps of the specimen under test. Results of the investigation match well with other slope-mapping techniques. Validation of experimental results with theoretical predictions in the case of a cantilever beam specimen has been undertaken. Accuracy of about 4.7% with respect to theoretical predictions is obtained.

X-ray phase tomography with a Talbot interferometer in combination with an X-ray imaging microscope

An X-ray Talbot interferometer was combined with an X-ray imaging microscope to generate differential phase contrast. X-ray phase tomography was attained based on the measurement of the differential phase shift using the fringe scanning method. Polymer blend samples were observed and phase separation structures were depicted. The spatial resolution was 1.3 μm in this test experiment, which will be easily improved by increasing the magnification.

X-ray microscopy for neural circuit reconstruction

Neural circuits in the central nervous system build our various higher brain functions. However, little is known about mechanisms underlying neuronal information processing in the brain. Anatomical graph structures of real neural networks will provide us with fundamental views to elucidate them. We aim at developing a three-dimensional atlas of neural circuits using high resolution hard X-ray microscopy by synchrotron radiation. We stained neurons of a complete brain from a mouse by the Golgi-Cox method. The heavy metals used in our procedure enhanced X-ray absorption and phase contrast. 3D images of fibriform axons and dendrites of various neurons were reconstructed by back projection. X-ray microscopy with a Talbot interferometer demonstrated finer histological structures of pyramidal neurons in the hippocampus and the cerebral cortex. This observation probably serves as a foundation for achieving a mammalian Connectome Project (identifying complete wiring diagrams of the brain) with X-ray nano-tomography in the near future.

High-speed X-ray phase imaging and X-ray phase tomography with Talbot interferometer and white synchrotron radiation

X-ray Talbot interferometry, which uses two transmission gratings, has the advantage that broad energy bandwidth x-rays can be used. We demonstrate the use of white synchrotron radiation for high-speed X-ray phase imaging and tomography in combination with an X-ray Talbot interferometer. The moiré fringe visibility over 20% was attained, enabling quantitative phase measurement. X-ray phase images with a frame rate of 500 f/s and an X-ray phase tomogram with a scan time of 0.5 s were obtained successfully. This result suggests a breakthrough for time-resolved three-dimensional observation of objects that weakly absorb X-rays, such as soft material and biological objects.

An electron Talbot interferometer

We report the first demonstration of a Talbot interferometer for electrons. The interferometer was used to image the Talbot carpet behind a nano-fabricated material grating. The Talbot interferometer design uses two identical gratings, and is particularly sensitive to distortions of the incident wavefronts. To illustrate this we used our interferometer to measure the curvature of concave wavefronts in a weakly focused electron beam. We describe how this wavefront curvature demagnified the Talbot revivals, and we discuss further applications for electron Talbot interferometers.

Fabrication of X-Ray Gratings Using X-Ray Lithography Technique for X-Ray Talbot Interferometer

The X-ray radiographic imaging technique is very important in medical, biological, inspection, material science, and other fields. However, it is not enough to obtain a clear X-ray image of samples with low absorbance materials, such as biological soft tissues. Then, we have used an X-ray phase-imaging method of an X-ray Talbot interferometer. In this method, X-ray gratings were required to have a narrow pitch and high aspect ratio structure. Therefore, we have developed and fabricated high-aspect-ratio X-ray gratings with a pitch of , a height of , and a large effective area of using X-ray lithography and narrow electroforming techniques. In this paper, we discuss the fabrication process of X-ray gratings with a narrow pitch and high-aspect-ratio structure, and results of X-ray phase tomography using an X-ray Talbot interferometer with these X-ray gratings.

Fabrication of High Aspect Ratio X-ray Grating Using X-ray Lithography

X-ray radiographic imaging technique has found applications in various fields. However, it is not enough to get clear X-ray images of samples with low absorbance, such as biological soft tissues. To resolve this problem, we proposed a method using an X-ray Talbot interferometer of X-ray phase imaging. In this X-ray Talbot interferometer, X-ray gratings were required to have a fine, high accuracy, high aspect ratio structure. Then, we have developed and succeeded high aspect ratio X-ray gratings with a pitch of 5.3 μm and a height of 30 μm using X-ray lithography technique. We discuss that the X-ray gratings having a large effective area in order to obtain imaging size of practical use in medical application. In currently study, we have fabricated the X-ray gratings with a large effective area of 60 mm×60 mm. And, we conducted X-ray phase tomography of mouse at the chest and abdominal using X-ray Talbot interferometer. As a result, we successfully observed soft tissues and high density tissues. With the aim of broadening a field of view, we try to fabricate X-ray gratings that have a pitch of below 5.3 μm and larger area of 100 mm square. This result suggests that X-ray Talbot interferometer is a novel and simple method for phase sensitive X-ray radiography.

Fiber Bragg grating inscription combining DUV sub-picosecond laser pulses and two-beam interferometry

The combination of fiber Bragg grating inscription with femtosecond laser sources and the usage of the Talbot interferometer setup not only gives access to the fabrication of Bragg gratings in new types of materials but also allows, at the same time, to keep the high flexibility of an interferometric setup in choosing the Bragg grating wavelength. Since the spatial and temporal coherence properties of the femtosecond laser source differ strongly from those of conventional laser sources, specific limits and tolerances in the interferometric setup have to be considered. Such limits are investigated on the basis of an analytical ray tracing model. The results are applied to tolerance measurements of fiber Bragg grating reflections recorded with a DUV sub-picosecond laser source at 262 nm. Additionally we demonstrate the wavelength versatility of the two-beam interferometer setup for femtosecond inscription over a 40 nm wavelength band. Inscription experiments in Al/Yb doped silica glasses are demonstrated as a prove for the access to non-photosensitive fibers.

Fabrication of X-ray Grating Using X-ray Lithography Technique

X-ray radiographic imaging technique is very important in medical, biological, inspection, material science, and so on. However, it is not enough to obtain clear X-ray images of samples with low absorbance materials, such as biological soft tissues. Then, we have used an X-ray phase imaging method of an X-ray Talbot interferometer. In this method, X-ray gratings were required to have narrow pitch and high aspect ratio structure. Therefore, we have developed and fabricated high aspect ratio X-ray gratings with a pitch of 5.3 um, a height of 30 um, and a large effective area of 100 mm × 100 mm using X-ray lithography and narrow electroforming technique. In this paper, we discuss the fabrication process of X-ray gratings and results of X-ray phase tomography using an X-ray Talbot interferometer with these X-ray gratings.

Sensitivity of X-ray Phase Imaging Based on Talbot Interferometry

The sensitivity of X-ray phase imaging based on Talbot interferometry is discussed. In order to evaluate the superiority of the technique to the conventional absorption-contrast method, which relies on X-ray absorption, a criterion is proposed. An experimental result of X-ray phase imaging with a Talbot interferometer is compared with the criterion. The criterion is also available for X-ray phase imaging based on Talbot–Lau interferometry. The advantage of X-ray phase imaging based on Talbot(–Lau) interferometry is more prominent when smaller structures are observed with smaller pixels.

Efficiency of capturing a phase image using cone-beam x-ray Talbot interferometry

We assesses the efficiency of x-ray Talbot interferometry (XTI), a technique based on the Talbot effect for measuring a wavefront gradient, in terms of how quickly it can capture a high-quality phase image with a large signal-to-noise ratio for a given incident photon number. Photon statistics cause errors in the phase of the moiré fringes and impose a detection limit on the wavefront gradient. The relation between the incident photon number and the detection limit is determined, and a figure of merit of XTI for a monochromatic cone beam is then defined. The dependence of the figure of merit on optical system parameters, such as grating pitch and position, is then discussed. The effects of varying the pattern height and linewidth of the second grating are shown for rectangular and trapezoidal teeth. Finally, we show how to design a practical cone-beam Talbot interferometer for certain boundary conditions.

Waveguides and gratings fabrication in zirconium-based organic/inorganic hybrids

Sol–gel derived poly(oxyethylene)/siloxane organic/inorganic di-ureasil hybrids containing different amounts of methacrylic acid (McOH, CH2=C(CH3)COOH)) modified zirconium oxo-clusters (Zr-OMc) were processed as thin films deposited in glassy substrates via spin coating and as transparent and shape controlled monoliths. Channel monomode waveguides and diffraction gratings were UV patterned using the Talbot interferometer and the Lloyd mirror interferometer experimental setups. The time dependence of the diffraction gratings efficiency was studied for hybrids containing different amounts of Zr-OMc. Finally, the number of propagating modes and the refractive index gradient within the waveguide region, determined as a Gaussian section located below the patterned channel, was evaluated and modeled, a maximum index contrast of 2.43 × 10−5 being estimated.

Generation and characterization of first order fiber Bragg gratings with Bragg wavelengths in the visible spectral range

Using a combination of phase mask and interferometric inscription technique we have generated 1st order fiber Bragg gratings (FBGs) with resonance wavelengths in a wide range of the visible spectrum (VIS). We use a modified Talbot interferometer which offers great flexibility in Bragg wavelength, spatial grating length and reflectivity. Gratings with shortest grating lengths of less than 1mm and with reflectivities of more than 70% have been produced. Peak reflectivities of up to 99% have been achieved in the visible spectrum. FBGs in the visible spectral range require structure sizes in the sub 100 nm scale. Potential applications are in the field of laser and sensor technology.

Fabrication of large area diffraction grating using LIGA process

X-ray imaging is a very important technology in the fields of medical, biological, inspection, material science, etc. However, it is not enough to get the clear X-ray imaging with low absorbance. We have produced a diffraction gratings for obtaining high resolution X-ray phase imaging, such as X-ray Talbot interferometer. In this X-ray Talbot interferometer, diffraction gratings were required to have a fine, high accuracy, high aspect ratio structure. Then, we succeeded to fabricate a high aspect ratio diffraction grating with a pitch of 8 μm and small area using a deep X-ray lithography technique. We discuss that the diffraction gratings having a narrow pitch and an large effective area to obtain imaging size of practical use in medical application. If the pitch of diffraction gratings were narrow, it is expected high resolution imaging for X-ray Talbot interferometer. We succeeded and fabricated the diffraction grating with pitch of 5.3 μm, Au height of 28 μm and an effective area of 60 × 60 mm2.

Temporal impulse response of the Talbot interferometer

The Talbot interferometer has been shown earlier to act as an optical tapped delay-line in the time domain. The interferometer is based on the self-imaging effect. It consists of two gratings separated by a multiple of the self-imaging distance. Here, we determine its temporal behaviour experimentally. First, the impulse response is measured directly in the time domain by means of femtosecond pulse technology and second, by spectroscopy we measure its power spectrum. Results confirm earlier theoretical considerations.