Diffraction Imaging System Research Articles

闪光X射线衍射成像系统设计及实验方法

闪光X射线衍射成像系统设计及实验方法

Design and testing of infrared diffractive telescope imaging optical systems

Diffractive telescope is an updated imaging technology, it differs from conventional refractive and reflective imaging system, which is based on the principle of diffraction image. However, one of the great challenges of design this optical system is that the diffractive optical element focuses on different wavelengths of light at different points in space, thereby distorting the color characteristics of image. In this paper, we designs a long-wavelength infrared diffractive telescope imaging system with flat surface Fresnel lens and cancels the infrared optical system chromatic aberration by another flat surface Fresnel lens, achieving broadband light (from 8μm to 12μm) to a common focus. At last, the diffuse spot size and MTF function provide diffractive-limited performance.

Limited-angle hybrid optical diffraction tomography system with total-variation-minimization-based reconstruction

The case of diffraction tomography with limited angle of projections is discussed from the algorithmic and experimental points of view. To reconstruct a three-dimensional distribution of refractive index of a micro-object under study, we use a hybrid approach based on the simultaneous algebraic reconstruction technique (SART) enhanced by a compressed sensing reconstruction technique. It enables us to apply the standard computed tomography algorithms (which assume that the rays are traveling in straight lines through the object) for phase data obtained by means of digital holography. We present the results of analysis of a phantom and real objects obtained by applying SART with anisotropic total variation (ATV) minimization. The real data are acquired from an experimental setup based on a Mach–Zehnder interferometer configuration. Also, it is proven that in the case of simulated data, the limited number of projections captured in a limited angular range can be compensated by a higher number of iterations of the algorithm. We also show that the SART + ATV method applied for experimental data gives better results than the data replenishment algorithm.

用于空间望远镜的膜光子筛

According to the requirements of a space diffraction imaging system for large-aperture, weight-lightening and space deployable, a new diffraction optical element, PI photon sieve, was designed and fabricated. Firstly, the design theory of PI photon sieve was analyzed and the design parameters for an amplitude photon sieve were given according to the characteristics and the principle of space applications. Then, the mechanical structure of the photon sieve was designed by using UG software and a PI membrane photon sieve was successfully manufactured by employing micro-fabrication methods including e-beam vacuum coating, photolithography and wet etching. Finally, the diffraction efficiency of the PI photon sieve was measured and the imaging performance was tested. The experimental results show that the diffraction efficiency of photon sieve is 4.916% at the wavelength of 632.8 nm, which is about 73.9% of the theoretical value. For the star testing, by choosing the star hole with a diameter of 10 m and using a He-Ne laser for the light source, an ideal Airy disc with a diameter of 176.70 m was obtained, which is very close to the theoretical value, and the error is only 4.04%. For the imaging experiments, the maximum resolution of the photon sieve is measured to be 12.2 lp/mm, which is close to the spatial frequency limit of 14.4 lp/mm. It is shown that the experimental results are generally in agreement with the theoretical results. Comparing with other diffractive elements, PI photon sieve satisfies the application requirement of the primary mirror used in a space telescope for its lighter weight and better imaging performance.

Modulation of shape and polarization of beam using a liquid crystal q-plate that is fabricated via photo-alignment

A liquid crystal (LC) device, called a "q-plate" (QP), which is based on axially symmetric photo-alignment was investigated. The electrically tunable LC QP device could be modulated to control the shape and polarization of a linearly polarized Gaussian laser beam that propagated through it. The intensity profile and polarization distribution were simulated by MATLAB and 1D-DIMOS. The results of the simulation were consistent with experimental findings. In the fabricated electrically tunable LC QP device, switching between different beam-profile configurations can be realized by applying a voltage. Moreover, the fabrication of an LC QP is relatively simple, and the device has potential for such practical applications as beam shape modulators and spatial polarization converters use in diffractive optics and imaging systems.

Reconstructing state mixtures from diffraction measurements

Progress in imaging and metrology depends on exquisite control over and comprehensive characterization of wave fields. As reflected in its name, coherent diffractive imaging relies on high coherence when reconstructing highly resolved images from diffraction intensities alone without the need for image-forming lenses. Fully coherent light can be described adequately by a single pure state. Yet partial coherence and imperfect detection often need to be accounted for, requiring statistical optics or the superposition of states. Furthermore, the dynamics of samples are increasingly the very objectives of experiments. Here we provide a general analytic approach to the characterization of diffractive imaging systems that can be described as low-rank mixed states. We use experimental data and simulations to show how the reconstruction technique compensates for and characterizes various sources of decoherence quantitatively. Based on ptychography, the procedure is closely related to quantum state tomography and is equally applicable to high-resolution microscopy, wave sensing and fluctuation measurements. As a result, some of the most stringent experimental conditions in ptychography can be relaxed, and susceptibility to imaging artefacts is reduced. Furthermore, the method yields high-resolution images of mixed states within the sample, which may include quantum mixtures or fast stationary stochastic processes such as vibrations, switching or steady flows.

Development and characterization of a laboratory based X-ray diffraction imaging system for material and tissue characterization

Soft tissues feature a degree of short-range order, giving rise to diffraction patterns with broader peaks than crystalline materials. For this reason, an X-ray diffraction system (XRD) for characterization of soft tissue has less stringent requirements in terms of momentum transfer resolution than the one aimed at characterizing crystalline materials. We present results on the characterization of two energy-dispersive XRD systems. The first was based on conical collimation at 5.9° and the second was based on linear collimation at varying angles between 2° and 10°. The systems include a CdTe detector and a W-anode X-ray source. The angular resolution was measured as a function of sample thickness and scattering angle. Preliminary results confirm the effectiveness of the method for the characterization of biological tissues, showing insensitivity to small changes in angular acceptance and sample thickness, also showing it is possible to combine scattering data obtained at different angles.

Generation 2 testbed of Fresnel imager: first results on the sky

We present and discuss the first sky images obtained with a second generation "Fresnel Diffractive Array Imager" (FDAI) prototype. These im- ages have been made on high contrast multiple stars (STF-1273 and BU-893), and on Saturn. The focusing objective: a 200 × 200 mm "Fresnel array", is a 50 μm-thick opaque foil featuring approximately 250,000 specially shaped void apertures, corresponding to 696 Fresnel zones. It focusses light by diffraction. This prototype has been installed in parallel to the 76 cm "grand equatorial" (17.89 m focal length) at the Observatoire de la Cote d'Azur ,( Nice, France). The Fresnel array is attached close to the front end and on the side of the 19 m long refractor's tube. The "receiver module" (field optics, chromatic corrector and cameras) is placed at prime focus of the Fresnel array, and attached to the refractor tube close to the rear end. The chromatic correction in the receiver module is adapted to 800 nm, but operates successfully in the two spectral bands used: 630-745 nm and 750-950 nm. This setup has been used to test the on-sky capabilities of the diffractive imaging system in angular resolution, limiting magnitude and contrast, and to experience some of the situations that will be encountered in a future space-borne formation flying configuration. We have obtained high contrast diffraction-limited images of various celestial

Transmission diffraction-tomography system using a high-energy X-ray tube

A high-energy bench-top energy dispersive X-ray diffraction (EDXRD) system for 3-dimensional mapping of the crystalline structure and phase transformations in steel is described, for which preliminary data and system development are presented here. The use of precision tungsten slit screens with up to 225 keV X-rays allows for diffraction through samples of 304 L austenitic stainless steel of thickness 3-10 mm, while sample positioning is carried out with a precision goniometer and translation stage system.

Performance limitations of the pixelated ERD detector with respect to imaging using the rapid Tomographic Energy Dispersive Diffraction Imaging system

A prototype X-ray imaging system, using the principle of Tomographic Energy Dispersive Diffraction Imaging (TEDDI) has been developed at the University of Manchester's School of Materials. The non-destructive 3D imaging system makes use of a state of the art collimator array and a pixellated Si energy resolving detector. The new rapid TEDDI system is limited to thin, low density materials due to the low stopping power of Si at higher X-ray energies. In this paper the results of substituting Si for CdZnTe as the active detection element and limitations to the key parameters of energy resolution and count rate, for the detectors is presented. The findings have led to the design of a new ASIC which is discussed.

Numerical study of grating-assisted optical diffraction tomography

We study the resolution of an optical diffraction tomography system in which the objects are either in an homogeneous background or deposited onto a glass prism, a prism surmounted by a thin metallic film or a prism surmounted by a metallic film covered by a periodically nanostructured dielectric layer. For all these configurations, we present an inversion procedure that yields the map of the relative permittivity of the objects from their diffracted far field. When multiple scattering can be neglected, we show that the homogeneous, prism, and metallic film configurations yield a resolution about $\ensuremath{\lambda}∕4$ while the grating substrate yields a resolution better than $\ensuremath{\lambda}∕10$. When Born approximation fails, we point out that it is possible to neglect the coupling between the object and the substrate and account solely for the multiple scattering within the objects to obtain a satisfactory reconstruction. Last, we present the robustness of our inversion procedure to noise.

Tomographic reconstruction of weak, replicated index structures embedded in a volume

Measurements of weak, embedded index structures are important for material characterization of photopolymers, glass and other optical materials as well as for characterization of fabricated structures such as waveguides. We demonstrate an optical diffraction tomography system capable of measuring deeply-buried, weak, fabricated index structures written in a homogeneous volume. High-fidelity cross sections of these weak index structures are constructed by replicating the structure to be measured to form a diffraction grating. The coherent addition of scattering from each of these objects increases the sensitivity of the imaging system. Measurements are made in the far field, without the use of lenses, eliminating phase aberration errors through thick volumes.

Linear to axial or radial polarization conversion using a liquid crystal gel

Two types of liquid crystal (LC) gels with radial or twisted-radial molecular orientation are fabricated using a radial electric field generated by an indium-tin-oxide hole electrode in the bottom substrate. If the top substrate is not buffed, the radial-type LC gel is formed which can convert linearly polarized light into axially polarized light. On the other hand, if the top substrate is homogeneously buffed, then a twisted-radial LC gel is produced which can convert linearly polarized light into radially polarized light. These polarization converters are useful for diffractive optics and optical imaging systems.

Development of a new photon diffraction imaging system for diagnostic nuclear medicine

The objective of this project is to develop and construct an innovative imaging system for nuclear medicine and molecular imaging that uses photon diffraction and is capable of generating 1–2 mm spatial resolution images in two or three dimensions. The proposed imaging system would be capable of detecting radiopharmaceuticals that emit 100–200 keV gamma rays which are typically used in diagnostic nuclear medicine and in molecular imaging. The system is expected to be optimized for the 140.6 keV gamma ray from a Tc-99m source, which is frequently used in nuclear medicine. This new system will focus the incoming gamma rays in a manner analogous to a magnifying glass focusing sunlight into a small focal point on a detector’s sensitive area. Focusing gamma rays through photon diffraction has already been demonstrated with the construction of a diffraction lens telescope for astrophysics and a scaled-down lens for medical imaging, both developed at Argonne National Laboratory (ANL). In addition, spatial resolutions of 3 mm have been achieved with a prototype medical lens. The proposed imaging system would be comprised of an array of photon diffraction lenses tuned to diffract a specific gamma ray energy (within 100–200 keV) emitted by a common source. The properties of photon diffraction make it possible to diffract only one specific gamma ray energy at a time, which significantly reduces scattering background. The system should be sufficiently sensitive to the detection of small concentrations of radioactivity that can reveal potential tumor sites at their initial stages of development. Moreover, the system’s sensitivity would eliminate the need for re-injecting a patient with more radiopharmaceutical if this patient underwent a prior nuclear imaging scan. Detection of a tumor site at its inception could allow for an earlier initiation of treatment and wider treatment options, which can potentially improve the chances for cure.

A new, rapid 3D tomographic energy dispersive diffraction imaging system for materials characterisation and object imaging (rapid TEDDI)

A new, rapid 3D tomographic energy dispersive diffraction imaging system for materials characterisation and object imaging (rapid TEDDI)

Electron Backscattered Diffraction (EBSD) with a Cold Held Emission Gun (cFEG) SEM: Resolution, Sensitivity and Applications

A thorough and complete assessment of microstructure of materials requires a wide variety of analytical techniques, which should be sensitive to at all length scales - from mms to atomic scale. While there have been rapid advances in imaging and spectroscopy techniques for microstructural analysis - at all length scales, techniques for crystallographic analysis of microstructure have primarily relied on bulk x-ray/neutron diffraction and TEM. X-ray and neutron diffraction techniques, though very powerful, are primarily bulk techniques and extraction of local crystallography is formidable if not impossible. On the other hand, TEM diffraction techniques provide precise crystallographic information, but at a much smaller length-scale and suffer from poor statistics and tedious specimen preparation procedures. With the advent of commercially available electron backscattered diffraction (EBSD) and orientational imaging (OIM) systems for SEM, and sophisticated pattern recognition procedures, it is now possible to bridge the length-scale gap between bulk and TEM diffraction techniques.

High‐speed data acquisition in a diffraction tomography system employing large‐scale toroidal arrays

This report describes the development of an experimental system for ultrasound computed tomography and its application to breast imaging. Details of the system design and methods of high-speed data acquisition are presented. The method uses low-power discrete frequency sound in the range of 0.3–1.2 MHz, two cylindrical arrays of 512 and 1024 PZT transducers, high spatial sampling of the wavefront, and unique diffraction tomographic reconstruction methods. One transducer at a time is activated and allowed to reach steady state at which point the remaining measure phase and amplitude of the ultrasound signal. A total of 64 MB of data are acquired in <1 s for the 512-element array and 128 MB in <3 s for the 1024 array. Several algorithms have been developed to produce the diffraction tomogram which is reconstructed as either a 512 × 512 or 1024 × 1024 matrix of the scattering potential of the object dependent on speed of sound and attenuation. The effects of aberration are greatly diminished by a hybrid iterative algorithm. To date, human images have been made of the female breast which show good depiction of glandular structures and differentiation of gland and fat, and the coronal format provides a novel of the entire breast in life-size display. The results demonstrate that the technique provides a unique quantitative ultrasound image with high resolution over a very large global field of view of the breast. The method shows promise for improved imaging of the breast. © 1997 John Wiley & Sons, Inc. Int J Imaging Syst Technol, 8: 137–147, 1997

High-speed data acquisition in a diffraction tomography system employing large-scale toroidal arrays

High-speed data acquisition in a diffraction tomography system employing large-scale toroidal arrays

High‐speed data acquisition in a diffraction tomography system employing large‐scale toroidal arrays

High‐speed data acquisition in a diffraction tomography system employing large‐scale toroidal arrays

In situ laser optical particle sizing

The fragile nature of natural suspended particle aggregates and the consequent need for non-destructive methods of analysing their size distribution are reviewed. The advantages and limitations of laser diffraction apparatus and the performance of an in situ diffraction instrument are discussed in relation to an intercalibration exercise on the Elbe estuary. The potential for sizing fragile aggregates in highly turbid estuarine environments using a novel optical back scattering technique which overcomes many of the problems of laser diffraction, optical beam and optical imaging systems is considered.