Absorption Imaging Research Articles

Development of energy-dispersive diffraction and grayscale quantification in polychromatic synchrotron tomography

Synchrotron white-beam tomography has important applications for temporally evolving or highly absorbing samples. The polychromatic nature of the white beam results in beam hardening artifacts unless measures are taken to correct these artifacts. Moreover, while the absorption tomography data show the morphology of samples, for some applications, the ability to probe crystallographic phase would enhance both the interpretation of the tomography data and the overall understanding of the sample. This work will describe developments at the 7-BM beamline of the Advanced Photon Source to both effectively correct for the polychromatic nature of the white beam and to provide energy-dispersive diffraction data which can be coupled with white-beam tomography.

A review of in situ/operando studies of heterogeneous catalytic hydrogenation of CO2 to methanol

Repurposing CO2 into chemicals, one of the Carbon Dioxide Removal (CDR) strategies, still faces significant challenges in conversion and energy efficiency due to the lack of effective catalysts and processes. Fundamental understanding through in situ/operando investigations of the reaction mechanisms and catalyst structures is pivotal for developing the efficient catalysts. This paper reviews the past and recent in situ/operando studies of methanol synthesis from heterogeneous CO2 hydrogenation over a few typical catalysts including Cu-based, oxide-based, and noble-metal-based catalysts. With the development of high-pressure reactors, in situ/operando IR, X-ray absorption spectroscopy (XAS), X-ray diffraction (XRD), neutron diffraction and imaging have been used to reveal the surface intermediates and structures of working catalysts under CO2 hydrogenation conditions. On the one hand, the combined operando techniques shed light on working mechanisms for some catalytic systems. On the other hand, due to the complexity of selective CO2 hydrogenation reaction and limited sensitivity of current accessible operando techniques to the surface structure of catalysts, it is still murky about the exact nature of the active sites at the surface/interface and how different sites promote different reaction paths. It is concluded that new methodologies for differentiating signals from different sites, and the development of surface-sensitive techniques for high pressure reactions are needed for providing structural descriptors of highly active and selective CO2 conversion catalysts.

Quantum-enabled ghost imaging for non-invasive imaging of plants.

Imaging biological processes in plants, such as water transport and sequestration, without disturbing natural growth or introducing artificial stimuli is challenging. Most optical microscopy techniques involve fluorescent probes and/or high-intensity light to obtain structural and chemical signatures. Spatially resolved near-infrared (NIR) absorption, for example, captures information about chemical signatures, but is typically obtained with time-intensive scanned confocal techniques because there are few spatially-resolvable detectors (cameras) in the NIR. Furthermore, confocal microscopy illuminates living samples with significant light intensities that can damage or alter the organism. To image chemical signatures, such as water, in undisturbed plants, we developed a quantum ghost imaging microscope that leverages non-degenerate spontaneous parametric down conversion (SPDC). Samples are probed with low levels of NIR light. Due to quantum correlation with their visible SPDC photon pairs, an image of the NIR absorption can be obtained using a spatially-resolving detector in the visible. We describe the operating principle and first measurements of this new imaging technique.

Semiempirical criterion for eliminating wraparound artifacts in single-grid-based phase-contrast X-ray imaging

Single-grid-based phase-contrast X-ray imaging (SG-PCXI) is a non-interferometric method for the simultaneous retrieval of absorption, phase-contrast (differential), and dark-field images from a single exposure with a common X-ray grid using a spatial harmonic imaging (SHI) technique. However, the retrieved images are often distorted by the wraparound artifacts that are caused by the spectral overlap of adjacent harmonic peaks in the Fourier domain, resulting in the degradation of image quality. In this study, a semiempirical criterion required for eliminating wraparound artifacts in SG-PCXI was established by considering two constraints: one to resolve periodic grid strips by the system resolution to use the SHI technique, and the other to ensure that the spectral contents of adjacent harmonic peaks are separated (not overlapped) to the greatest possible extent during data processing. Further, we assumed that the system resolution can be experimentally determined as the spatial frequency at a 10% modulation transfer function. To verify the efficacy of the semiempirical criterion, we conducted an experiment using a table-top setup, which primarily comprised a microfocus X-ray source with a 20 μm focal spot size, X-ray grids with strip densities of 150, 200, and 254 lines/inch, and a CMOS flat-panel detector with a 49.5 μm pixel size. The experimental measurements of the wraparound artifacts in our system setup were in good agreement with the semiempirical criterion over the entire range of test conditions, thus verifying its efficacy for SG-PCXI. Accordingly, the semiempirical criterion established in this study will be useful for designing a wraparound artifact-free system layout in SG-PCXI.

A versatile laboratory setup for high resolution X-ray phase contrast tomography and scintillator characterization.

X-ray micro-tomography (μCT) is a powerful non-destructive 3D imaging method applied in many scientific fields. In combination with propagation-based phase-contrast, the method is suitable for samples with low absorption contrast. Phase contrast tomography has become available in the lab with the ongoing development of micro-focused tube sources, but it requires sensitive and high-resolution X-ray detectors. The development of novel scintillation detectors, particularly for microscopy, requires more flexibility than available in commercial tomography systems. We aim to develop a compact, flexible, and versatile μCT laboratory setup that combines absorption and phase contrast imaging as well as the option to use it for scintillator characterization. Here, we present details on the design and implementation of the setup. We used the setup for μCT in absorption and propagation-based phase-contrast mode, as well as to study a perovskite scintillator. We show the 2D and 3D performance in absorption and phase contrast mode, as well as how the setup can be used for testing new scintillator materials in a realistic imaging environment. A spatial resolution of around 1.3μm is measured in 2D and 3D. The setup meets the needs for common absorption μCT applications and offers increased contrast in phase contrast mode. The availability of a versatile laboratory μCT setup allows not only for easy access to tomographic measurements, but also enables a prompt monitoring and feedback beneficial for advances in scintillator fabrication.

Mammalian Cornea Inspired Anti‐Fogging Silica Glass Surface Achieved by Femtosecond Laser

AbstractFog generation can severely damage optical systems by degrading the light absorption rate and imaging quality of optical components. Furthermore, fog can reduce the light flux and transmittance of the optical system, resulting in poor imaging clarity and contrast. Studies have focused on minimizing fog formation and effects. Drawbacks such as high energy consumption and waste pollution severely limit the application of conventional methods. However, achieving high fog resistance of optical components remains a challenge. A novel method of fabricating anti‐fogging slippery surfaces (inspired by the anti‐fog mechanism of the mammalian cornea) on silica glass by using femtosecond lasers is proposed to achieve durable and environment‐friendly optical devices that can achieve anti‐fogging in real time. The femtosecond laser wet etching method is used to fabricate the inside cabin of glass. The cabin filled with graphene spontaneously heats the sample under sunlight to prevent fog formation. In addition to exhibiting excellent anti‐fogging characteristics, the prepared sample achieves high optical transmittance, high durability, and excellent self‐repair capability. Thus, the proposed method exhibits considerable potential for application in numerous domains.

Virtual differential phase-contrast and dark-field imaging of x-ray absorption images via deep learning.

Weak absorption contrast in biological tissues has hindered x-ray computed tomography from accessing biological structures. Recently, grating-based imaging has emerged as a promising solution to biological low-contrast imaging, providing complementary and previously unavailable structural information of the specimen. Although it has been successfully applied to work with conventional x-ray sources, grating-based imaging is time-consuming and requires a sophisticated experimental setup. In this work, we demonstrate that a deep convolutional neural network trained with a generative adversarial network can directly convert x-ray absorption images into differential phase-contrast and dark-field images that are comparable to those obtained at both a synchrotron beamline and a laboratory facility. By smearing back all of the virtual projections, high-quality tomographic images of biological test specimens deliver the differential phase-contrast- and dark-field-like contrast and quantitative information, broadening the horizon of x-ray image contrast generation.

Single shot imaging for cold atoms based on machine learning

The ability to detect atoms in high spatiotemporal resolution provides a powerful tool for us to investigate the quantum properties of ultracold quantum gases. Plenty of useful imaging methods, including absorption imaging, phase contrast imaging and fluorescence imaging, have been implemented in detecting atoms. Among them, absorption imaging is the most widely used method in cold atoms laboratory. However, the traditional absorption imaging method is affected by perturbations such as interference between optical elements, fluctuation of laser power, frequency, and spatial position, resulting in residual spatially structured noise and degradation of imaging quality. Especially for regions with lower density or for longer time-of-flight, a large number of repetitions are often required to obtain better signal-to-noise ratio, which would increase the time cost and induce other noise. One must reduce the time between two imaging pulses to suppress the spatial noise. A better charge coupled device (CCD) with higher frame transfer rate or other method like fast-kinetic mode will be used to improve the imaging quality. In this paper, a single-shot cold atom imaging method based on machine learning is proposed, in which only one absorption imaging of cold atoms is required, and the corresponding background image can be generated through the neural network of an autoencoder. This effectively reduces the spatial striped noise in imaging, significantly improves the imaging quality, and makes it possible for cold atoms to be imaged multiple times in a single cycle.

Analysis and simulation of time-of-flight spectrum in Rb<sup>+</sup>-Rb hybrid trap

The time-of-flight mass spectrum of charged particles, which are created through two-step cw-laser photoionization of laser-cooled <sup>87</sup>Rb atoms in an ion-neutral hybrid trap, is quantitatively investigated to further facilitate the study of Rb<sup>+</sup>-Rb reactive collisions. A microchannel plate (MCP) is used to detect charged particles, and two spectral peaks corresponding to the <sup>87</sup>Rb<sup>+</sup> ions and the product <inline-formula><tex-math id="Z-20230423060254-1">\begin{document}$ \rm {}^{87}Rb_2^+ $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20222273_Z-20230423060254-1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20222273_Z-20230423060254-1.png"/></alternatives></inline-formula> of the Rb<sup>+</sup>-Rb reaction were observed in the time-of-flight spectrum, respectively. The two peaks overlapped with each other and both showed an asymmetric profile. The information about the intensity, position, and half-width of the peak for a specific ion species was derived by fitting the time-of-flight spectrum with the probability density function of the Gumbel distribution. Then the relative ion intensity was converted into absolute ion number through the following steps. The rate equation of the total number of ions, which includes the number of atoms, the calibration factor of MCP, and the effective decay rate of ions in the ion trap, was established by modeling the photoionization of atoms. Combined with the absolute number of atoms measured by absorption imaging, the calibration factor in converting the ion intensity into the ion number was derived and the relative ion intensity was converted into the absolute number of ions. This provides a method of calibrating the MCP. The reliability of our calibration method was proved by the fact that the calibration factor in converting the intensity measured by MCP into particle number is independent of the duration of photoionization, the intensity and wavelength of the ionizing laser. Moreover, in order to explain the relationship between the peak width and temperature of the corresponding ion species, the time-of-flight spectra of the ions trapped in the ion trap were simulated by using COMSOL Multiphysics. The simulation results demonstrated that the large ion kinetic energy results in a narrow spectral peak. In sum, we quantitatively analyze and simulate the time-of-flight spectrum of the photoionization of cold atoms in the Rb<sup>+</sup>-Rb hybrid trap. The absolute number of ions is obtained by the intensity of the spectral peak, and the width of the spectral peak is related to the temperature of the ions. These results lay a foundation for the in-depth analysis of the ion-atom reaction collision and charged particle temperature relaxation in the photoionization of cold atoms, and thus further elucidating the subsequent collisional dynamics of ultracold plasmas.

Optimization of beam arrangement for tunable diode laser absorption tomography reconstruction based on fractional Tikhonov regularization

Beam arrangement with limited projections based on tunable diode laser absorption spectroscopy is the key to achieving a more accurate two-dimensional reconstruction of the combustion. Using fractional calculus theory, a beam optimization method based on fractional Tikhonov regularization is proposed. The beam arrangement function based on fractional Tikhonov regularization is established by extending the standard Tikhonov regularization to fractional modes. The genetic algorithm is used to analyze the calculation results of different orders in a range of (0, 1), and the beam arrangement is obtained. Using 20 laser beams to scan the characteristic absorption spectrum of H<sub>2</sub>O in the near-infrared band 7185.6 cm<sup>–1</sup>, modeling the calculations in a 10×10 element discrete tomography domain, and comparing the reconstruction results of the five beam arrangements for different Gaussian distribution models, the beam arrangement based on fractional Tikhonov regularization shows more obvious advantages. This design method proposed in this work is valuable for the theoretical study of the optimal design of two-dimensional measurement beams based on the tunable diode laser absorption spectroscopy technique, which can promote the application of this technique in the two-dimensional reconstruction of complex engine combustion and combustion efficiency improvement.

Label-free visualization of photosynthetic microbial biofilms using mid-infrared photothermal and autofluorescence imaging.

The formation of photosynthetic microbial biofilms comprising multispecies biomolecules, such as extracellular polymeric substances (EPSs), and microbial cells play pivotal roles in maintaining or stimulating their biological functions. Although there are numerous studies on photosynthetic microbial biofilms, the spatial distribution of EPS components that are vital for microbial biofilm formation, such as exopolysaccharides and proteins, is not well understood. Visualization of photosynthetic microbial biofilms requires label-free methods, because labelling EPSs results in structural changes or aggregation. Raman spectroscopy is useful for label-free visualization of biofilm constituents based on chemical contrast. However, interference resulting from the bright autofluorescence of photosynthetic molecules and the low detection efficiency of Raman scattering make visualization a challenge. Herein, we visualized photosynthetic microbial biofilms in a label-free manner using a super-resolution optical infrared absorption imaging technique, called mid-infrared photothermal (MIP) microscopy. By leveraging the advantages of MIP microscopy, such as its sub-micrometer spatial resolution, autofluorescence-free features, and high detection sensitivity, the distribution of cyanobacteria and their extracellular polysaccharides in the biofilm matrix were successfully visualized. This showed that cyanobacterial cells were aligned along acidic/sulfated polysaccharides in the extracellular environment. Furthermore, spectroscopic analyses elucidated that during formation of biofilms, sulfated polysaccharides initially form linear structures followed by entrapment of cyanobacterial cells. The present study provides the foundation for further studies on the formation, structure, and biological functions of microbial biofilms.

DIAGNÓSTICO E TREINAMENTO POR TECNOLOGIA DE IMAGEM EM TRAUMATISMOS DO JOELHO NO BASQUETEBOL

ABSTRACT Introduction: The research and development of new methods of injury diagnosis and rehabilitation training in benefits to the health and training of athletes is a contemporary priority. Among modern techniques, diagnostic imaging technology stands out. Objective: Study the auxiliary effect of imaging technology in the diagnosis and rehabilitation training of functional knee joint injuries in basketball practice. Methods: 50 basketball players diagnosed and treated in the past four years for knee joint function injuries in a special hospital were selected, including 28 male and 22 female athletes, aged 17 to 25 years. PerkinElmer Spotlight-300 FTIR spectral imaging system was used to scan the articular cartilage sections, visible light and total absorption images of the samples were obtained by reflection mode imaging. Results: The peak infrared feature of the articular cartilage measured by the infrared spectrum imaging technology is very consistent with the FTIR spectrum. After rehabilitation training, the Y test score of female patients increased from 96.72 ± 6.05 to 105.40 ± 4.23, and the Y test score of male patients increased from 98.34 ± 5.33 to 105.51 ± 4.89, showing significant differences. Conclusion: Infrared spectrum imaging technology is an effective technique for identifying functional knee joint injury, and is of great use for diagnosis and training update in basketball players with knee trauma. Level of evidence II; Therapeutic studies - investigation of treatment outcomes.

Unified Modulation Pattern Analysis (UMPA) algorithm for 1D sensitive X-ray phase contrast imaging techniques

X-ray phase contrast imaging (XPCI) techniques are sensitive to refraction (differential-phase) and small-angle X-ray scattering (dark-field) signals, not measurable with conventional absorption imaging techniques. Among XPCI techniques, edge illumination (EI), grating interferometry (GI), and speckle-based imaging (SBI) make use of wavefront markers, such as absorbing masks with periodical apertures or random diffusers, to encode refraction and dark-field signals induced by the sample. The Unified Modulated Pattern Analysis (UMPA) provides an algorithmic solution to extract the transmission, refraction, and dark-field images from EI, GI, and SBI datasets where the wavefront marker is directly resolved by the employed detection system. In its original implementation, UMPA has been designed for XPCI techniques sensitive to refractions along two axes. This work presents a modified version of the algorithm to extend its applicability to all the existing XPCI techniques that use wavefront markers with sensitivity to refraction limited along one direction (UMPA-1D). The algorithm, written in C++ and Cython and parallelized with OpenMP, enables fast reconstruction times that are particularly convenient for large tomographic datasets. The validity of the UMPA-1D has been demonstrated using both simulated images and real acquisitions with an EI setup in beam-tracking mode.

Quantitative Tomographic Laser Absorption Imaging of Atomic Potassium during Combustion of Potassium Chloride Salt and Biomass.

Gaseous potassium (K) species play an important role in biomass combustion processes, and imaging techniques are powerful tools to investigate the related gas-phase chemistry. Here, laser absorption imaging of gaseous atomic K in flames is implemented using tunable diode laser absorption spectroscopy at 769.9 nm and a high-speed complementary metal oxide semiconductor (CMOS) camera recording at 30 kfps. Atomic K absorption spectra are acquired for each camera pixel in a field of view of 28 × 28 mm at a rate of 100 Hz. The technique is used to determine the spatial distribution of atomic K concentration during the conversion of potassium chloride (KCl) salt and wheat straw particles in a laminar premixed CH4/air flame with an image pixel resolution of up to 120 μm. Due to axisymmetry in setup geometry and, consequently, atomic K distributions, the radial atomic K concentration fields could be reconstructed by one-dimensional tomography. For the KCl sample, the K concentration field was in excellent agreement with previous point measurements. In the case of wheat straw, atomic K concentrations of around 3 ppm were observed in a cylindrical flame during devolatilization. In the char conversion phase, a spherical layer of atomic K, with concentrations reaching 25 ppm, was found within 5 mm of the particle surface, while the concentration rapidly decreased to sub-ppm levels along the vertical axis. In both cases, a thin (∼1 mm) layer without any atomic K was observed in close vicinity to the particle, suggesting that the potassium was initially not released in its atomic form.

Classical and quantum metrology of the Lieb-Liniger model

We study the classical and quantum Fisher information for the Lieb-Liniger model. The Fisher information has been studied extensively when the parameter is inscribed on a quantum state by a unitary process, e.g., Mach-Zehnder or Ramsey interferometry. Here, we investigate the case that a Hamiltonian parameter to be estimated is imprinted on eigenstates of that Hamiltonian, and thus is not necessarily encoded by a unitary operator. Taking advantage of the fact that the Lieb-Liniger model is exactly solvable, the Fisher information is determined for periodic and hard-wall boundary conditions, varying number of particles, and for excited states of type-I and type-II in the Lieb-Liniger terminology. We discuss the dependence of the Fisher information on interaction strength and system size, to further evaluate the metrological aspects of the model. Particularly noteworthy is the fact that the Fisher information displays a maximum when we vary the system size, indicating that the distinguishability of the wavefunctions is largest when the Lieb-Liniger parameter is at the crossover between the Bose-Einstein condensate and Tonks-Girardeau limits. The saturability of this Fisher information by the absorption imaging method is assessed by a specific modeling of the latter.

Acquisition of a single grid-based phase-contrast X-ray image using instantaneous frequency and noise filtering

BackgroundTo obtain phase-contrast X-ray images, single-grid imaging systems are effective, but Moire artifacts remain a significant issue. The solution for removing Moire artifacts from an image is grid rotation, which can distinguish between these artifacts and sample information within the Fourier space. However, the mechanical movement of grid rotation is slower than the real-time change in Moire artifacts. Thus, Moire artifacts generated during real-time imaging cannot be removed using grid rotation. To overcome this problem, we propose an effective method to obtain phase-contrast X-ray images using instantaneous frequency and noise filtering.ResultThe proposed phase-contrast X-ray image using instantaneous frequency and noise filtering effectively suppressed noise with Moire patterns. The proposed method also preserved the clear edge of the inner and outer boundaries and internal anatomical information from the biological sample, outperforming conventional Fourier analysis-based methods, including absorption, scattering, and phase-contrast X-ray images. In particular, when comparing the phase information for the proposed method with the x-axis gradient image from the absorption image, the proposed method correctly distinguished two different types of soft tissue and the detailed information, while the latter method did not.ConclusionThis study successfully achieved a significant improvement in image quality for phase-contrast X-ray images using instantaneous frequency and noise filtering. This study can provide a foundation for real-time bio-imaging research using three-dimensional computed tomography.

High-aperture EUV microscope using multilayer mirrors and a 3D reconstruction algorithm based on z-tomography.

The article is devoted to the development of an EUV microscope using a wavelength of 13.84 nm. Due to the use of a mirror lens with a large numerical aperture, NA = 0.27, and a short depth of focus, it has been possible to carry out z-tomography of bio-samples for the first time with this type of microscope. A 3D image was reconstructed, and a pixel resolution of 140 nm was obtained. A new simple algorithm for the 3D reconstruction of absorption images from z-tomography data has been proposed that takes into account lens aberrations and a point spread function. The algorithm reduces the inverse absorption task to the corresponding well-studied task of fluorescence microscopy, with an error of 10% for cells up to 10 µm thick.

Low-density foreign body detection in food products using single-shot grid-based dark-field X-ray imaging

This study presents a novel approach for detecting low-density foreign bodies (FBs) in food products using single-shot grid-based dark-field X-ray imaging (SG-DFXI). SG-DFXI obtains information related to the sample's small-angle X-ray scattering using a conventional X-ray source and grid. It is specifically utilized to detect low-density materials that are invisible when using conventional techniques. To demonstrate its efficacy, an experiment was conducted with food samples containing low-density FBs such as wood, Styrofoam, pencil lead, and soft plastic. A quantitative evaluation was conducted based on the contrast-to-noise ratio (CNR) and relative contrast gain (RCG). The proposed method detected low-density FBs barely visible in absorption images. Additionally, the CNR values measured in dark-field images were approximately 2.8–10.5 times larger than those in the absorption images, indicating that the proposed approach significantly improved the ability to detect low-density FBs in food samples. The RCG characteristic was improved as the system's autocorrelation length ( ξ G ) increased; the RCG value for ξ G = 453 nm was approximately 2.5 times larger than that for ξ G = 171 nm. • Method detecting low-density foreign bodies (FBs) in food products is proposed. • Single-shot grid-based dark-field X-ray imaging (SG-DFXI) method is used. • SG-DFXI obtains information related to samples' small-angle X-ray scattering. • The experiment used food samples with FBs like wood, Styrofoam, soft plastic, etc. • CNR and relative contrast gain (RCG) were used for quantitative evaluation.

High resolution UV spectral imaging and bio-detection with magnetic dipole quasi-BIC resonant dielectric metasurfaces

In this paper, we designed a ring-shaped metasurface based on diamond material that response in ultraviolet band, and with which the BIC mode is obtained by breaking the symmetry of its structural units. We show that only when the radiation rate of the magnetic dipole resonance of the BIC mode is equal to the dissipation loss brought by the surface covering material, the interaction between light and matter is maximally enhanced. The absorptivity of the film material is enhanced by an order of magnitude. The simulation results show that there is a linear relationship between the resonant positions of the structure and the scaling factor S varying structure sizes. When the metasurface is covered with a single DNA film, changes differently due to the absorption of the DNA. The reflection information of the system is further converted into ultraviolet absorption of DNA. Then the multiple absorption peaks form the absorption spectrum of DNA molecules. By Arranging the different scaling factor metasurface pixels on a same substrate we can obtain a specific absorption image. The absorptivity of DNA leads to the difference in brightness and darkness of the metasurface pixels, which can be processed into gray-scale images that give out the specific fingerprint information of the DNA. So, we realized calibration and analysis of DNA without spectroscopic measurements in the ultraviolet band now. The metasurface device can effectively detect the contamination of DNA by other biomolecules such as RNA. This work has great significance in promoting the application of metasurfaces in the field of biological detection and demonstrates that a specially designed metasurface can be applied in nucleic acid detection.

Uranium Dust Cloud Combustion: Burning Characteristics and Absorption Spectroscopy Measurements

This study characterized uranium metal dust cloud combustion using absorption spectroscopy, imaging, and broadband emission measurements. Other metals were similarly combusted to establish correlations between results from this study and those found in the literature. It was determined that the burn temperature of uranium was limited to the volatilization temperature of uranium dioxide. Combustion behavior was similar to that of other refractory metals in terms of burn time and the observation of exploding particle behavior.