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The phase imaging system that records the bandlimited image and its Fourier intensity (BIFT) is a single-shot phase retrieval method with the guarantee of uniqueness and global convergence properties. However, the resolution is limited by the bandlimited imaging system and cannot investigate detailed structures under diffraction limitations. Previous efforts to address such issues focused on synthetic aperture techniques but sacrificed time resolution. In this paper, we propose a single-shot super-resolution imaging method based on analytic extrapolation. Through imaging simulations, we have demonstrated that the resolution can be improved by 1.58 in the case of noise-free. Theoretical analysis in the presence of noise is also carried out, indicating that the enhancement of resolution was determined by signal-to-noise ratio, and the resolution can be enhanced by 1.14 to 1.34 at different signal-to-noise ratios. Based on the single-shot capability of BIFT, this method has the potential to achieve fast and high-throughput phase imaging. [ABSTRACT FROM AUTHOR]

The phase imaging system that records the bandlimited image and its Fourier intensity (BIFT) is a single-shot phase retrieval method with the guarantee of uniqueness and global convergence properties. However, the resolution is limited by the bandlimited imaging system and cannot investigate detailed structures under diffraction limitations. Previous efforts to address such issues focused on synthetic aperture techniques but sacrificed time resolution. In this paper, we propose a single-shot super-resolution imaging method based on analytic extrapolation. Through imaging simulations, we have demonstrated that the resolution can be improved by 1.58 in the case of noise-free. Theoretical analysis in the presence of noise is also carried out, indicating that the enhancement of resolution was determined by signal-to-noise ratio, and the resolution can be enhanced by 1.14 to 1.34 at different signal-to-noise ratios. Based on the single-shot capability of BIFT, this method has the potential to achieve fast and high-throughput phase imaging.

Imaging of phase objects behind scattering media is a challenging task. Intensity imaging through diffusers can be achieved based on digital holography by obtaining the complex amplitude of the diffuser in advance. As described in this paper, we experimentally demonstrate the reconstructed images of phase objects behind diffusers with different diffusion angles by digital holography. Using the complex amplitude information of the diffuser to correct the complex amplitude information of the object through the diffuser, the phase distribution of the object is obtainable behind the diffuser. Imaging of phase objects behind diffusers has been verified through experiments using a plano-convex lens and a wedge substrate as phase objects with various scattering angles. Quantitative analyses of the phase objects are performed. The lens shape can be visualized from the known refractive index. Moreover, the curvature radius can be estimated. [ABSTRACT FROM AUTHOR]

Implicit neural representation characterizes the mapping between the signal’s coordinate to its attributes, and has been widely used in the optimization of inverse problems by embedding the physics process into the loss function.However, the implicit neural representation is suffering the low convergence speed and accuracy from the random initialization of the network parameters.The meta-learning algorithm for providing implicit neural representation with a strong prior of network parameters was proposed, thus enhancing the optimization efficiency and accuracy for solving inverse problems.To address the important issue of lens less phase imaging, an intelligent method on phase imaging was proposed based on the snapshot lens less sensing model.By embedding the optical diffraction propagation theory into the design of loss function for implicit neural representation, the dependency of large-scale labelled dataset in traditional deep learning-based methods was eliminated and accurate phase image from a single diffraction measurement image was provided.Furthermore, the meta-learning model was introduced for initializing network to further improve the efficiency and accuracy of network training.Numerical simulation results show that the proposed method can achieve a PSNR improvement of more than 11 dB compared to the conventional method.The experimental results in real data show that the phase image reconstructed by the proposed method is clearer and has fewer artifacts.

This paper proposed a high-sensitivity phase imaging eddy current magneto-optical (PI-ECMO) system for carbon fiber reinforced polymer (CFRP) defect detection. In contrast to other eddy current-based detection systems, the proposed system employs a fixed position excitation coil while enabling the detection point to move within the detection region. This configuration effectively mitigates the interference caused by the lift-off effect, which is commonly observed in systems with moving excitation coils. Correspondingly, the relationship between the defect characteristics (orientation and position) and the surface vertical magnetic field distribution (amplitude and phase) is studied in detail by theoretical analysis and numerical simulations. Experiments conducted on woven CFRP plates demonstrate that the designed PI-ECMO system is capable of effectively detecting both surface and internal cracks, as well as impact defects. The excitation current is significantly reduced compared with traditional eddy current magneto-optical (ECMO) systems.

The results of measuring the surface depth of the test object using digital holography are presented. The resulting image was compared to a model based on the calibration slide documentation. In the presented holographic microscope, instead of an eyepiece, a lens with a geometric phase effect is used, which converts a beam with linear polarization into a pair of beams with circular polarizations (diverging and converging). The parallel phase shift method was used to obtain phase distribution. Using a polarization camera, four interferograms corresponding to four different linear projections of interfering waves with right and left circular polarizations were recorded in one exposure. Holograms of a phase object-micrometer were obtained, according to which, by the method of parallel phase shift, the distribution of phase lag introduced by the object was restored. To correct the aberration, subtraction of the recorded phase raid of the illuminating wave — the experimentally obtained phase of the wavefront without an object is used. The developed digital holographic phase microscope based on a geometric phase lens and a polarization camera makes it possible to correctly visualize the surface relief profile. The microscope can be used as a tool for monitoring the state of biological objects exposed to external effects.

Label‐free imaging and identification of fast‐moving cells is a very challenging task. A kind of phase flow cytometry using coherent modulation imaging was proposed to realize label‐free imaging and identification on fast‐moving cells with compact optical alignment and high accuracy. Phase image of cells under inspection could be computed qualitatively from their diffraction patterns at the accuracy of about 0.01 wavelength and the resolution of about 1.23 μm and the view field of 0.126 mm2. Since the imaging system was mainly composed by a piece of random phase plate a detector without using commonly adopted reference beam and corresponding complex optical alignment, this method has much compacter optical structure and much higher tolerance capability to environmental instability in comparison with other kinds of phase flow cytometry. Current experimental results prove it could be an efficient optical tool for label‐free tumor cell detection. [ABSTRACT FROM AUTHOR]

Phase imaging normally employs coherent a light source while an incoherent light source is not preferred due to its random wavefront. Another challenge for practical phase imaging is imaging through scattering media, which scatter the photons in a random manner and lead to seriously distorted images of speckles. Based on the convolutional neural network (CNN), this paper presents an approach for phase imaging through scattering media using an incoherent light source. A CNN was trained and utilized to reconstruct the target images from the captured images of speckles. Similarities of over 90% between the reconstructed images and their target images have been achieved. It was concluded that an incoherent light source can be used as an illumination source for scattering phase imaging with the assistance of deep learning technology. This phase imaging approach with an incoherent light source through scattering media can be used to record the refractive indices of transparent samples, which might lead to its application in biomedical imaging. [ABSTRACT FROM AUTHOR]

We consider the application of a recently developed hyperspectral broadband phase retrieval (HSPhR) technique for spectrally varying object and modulation phase masks at 100 spectral components. The HSPhR method utilizes advanced techniques such as Spectral Proximity Operators and ADMM to retrieve complex-domain spectral components from multiple spectral observations. These techniques filter out noisy observations and strike a balance between noisy intensity observations and their predicted counterparts, resulting in accurate retrieval of the broadband hyperspectral phase even for low signal-to-noise ratio components. Both simulation and physical experiments have confirmed the effectiveness of this approach. [ABSTRACT FROM AUTHOR]

Fourier transform holography overcomes the phase recovery challenge through recording complex field information of the object in an interference pattern recorded at the far field, i.e., Fourier plane. Moreover, this geometry helps to reconstruct the complex field of the object from a single Fourier transform, which is an attractive feature for the numerical reconstruction of the digitally recorded hologram. In this paper, we present a nearly common path experimental design for recording a digital Fourier holographic hologram using a beam displacer, and recover the complex valued objects using the Fourier analysis. The performance of the system is experimentally examined for different objects. [ABSTRACT FROM AUTHOR]

Phase loss is a typical problem in the optical domain, and optical detectors only measure the amplitude distribution of a signal without its phase. However, an optimal phase is desired in a variety of practical applications, such as optical metrology, nondestructive testing, and quantitative microscopy. Several methods have been proposed to quantitatively measure phase, among which interferometry is one of the most commonly used. An intensity interferometer has also been used to recover phase and enhance the phase difference measurement via the intensity correlation. In this paper, we present and examine another technique based on the Stokes correlation for enhancing phase measurement by a factor of two. The enhancement in phase measurement is accomplished through an evaluation of the correlation between two points of Stokes fluctuations of randomly scattered light and by recovering the enhanced phase of the object by using three-step phase shifting along with the Stokes correlations. This technique is expected to be useful for imaging and the experimental measurement of the phase of a weak signal. [ABSTRACT FROM AUTHOR]

A large number of carbon fiber reinforced polymers have been applied to aircraft and automobiles, and many nondestructive testing methods have been studied to detect their defects. Eddy current magneto-optical imaging nondestructive testing technology has been widely used in the detection of metal materials such as aircraft skin, but it usually requires a large excitation current and, at present, can only detect metal materials with high conductivity. In order to take full advantage of the innate benefits and efficiency of eddy current magneto-optic imaging and enable it to detect defects in carbon fiber reinforced polymers with weak conductivity, it is necessary to improve the magnetic field response of the eddy current magneto-optic imaging system and explore suitable excitation and detection methods. The scanning eddy current magneto-optical imaging nondestructive testing device built in this study has improved the magnetic field response of the system, and the eddy current magneto-optical phase imaging testing method has been proposed to detect the crack defects of carbon fiber reinforced polymers. The effectiveness of the method has been verified by simulation and experiment. [ABSTRACT FROM AUTHOR]

Interferometric detection enables the acquisition of the amplitude and phase of the optical field. By making use of the synthetic wavelength as a computational construct arising from digital processing of two off-axis digital holograms, it is possible to identify the shape of an object obscured by fog and further increase the imaging range due to the increased sensitivity in coherent detection. Experiments have been conducted inside a 27 m long fog tube filled with ultrasonically generated fog. We show the improved capabilities of synthetic phase imaging through fog and compare this technique with conventional active laser illumination imaging. [ABSTRACT FROM AUTHOR]

We demonstrate the formation of the near field with non-trivial phase distribution using surface plasmon interference devices, and experimental quantitative imaging of that phase with near-field phase microscopy. The phase distribution formed with a single device can be controlled by the polarization of the external illumination and the area of the device assigned to the object wave. A comparison of the experimental data to a numerical electromagnetic model and an analytical model assigns the origin of the near-field phase to the out-of-plane electric component of surface plasmon polaritons, and also verifies the predictive power of the models. We demonstrate a formation of near-field plane waves with different propagation directions on a single device, or even simultaneously at distinct areas of a single device. Our findings open the way to the imaging and tomography of phase objects in the near field.

Piezoelectric Transducer(PZT) plays a significant role for intelligent materials and structures for its better coupling compatibility with structures. The amplitude imaging is easily influenced by the grating and side lobes, while the phase imaging is disturbed by several random single-pixel highlighted spots. Considering that the combination of the amplitude and phase information, which can be acquired simultaneously by Hilbert transform, could introduce higher robustness and accurateness of damage detection, the array focused Hilbert holographic imaging method for Lamb wave is proposed. A0 mode and S0 mode are also combined to detect surface and inner defects through the logical operation. [ABSTRACT FROM AUTHOR]

Phase imaging of biochemical samples has been demonstrated for the first time at the Infrared Microspectroscopy (IRM) beamline of the Australian Synchrotron using the usually discarded near-IR (NIR) region of the synchrotron-IR beam. The synchrotron-IR beam at the Australian Synchrotron IRM beamline has a unique fork shaped intensity distribution as a result of the gold coated extraction mirror shape, which includes a central slit for rejection of the intense X-ray beam. The resulting beam configuration makes any imaging task challenging. For intensity imaging, the fork shaped beam is usually tightly focused to a point on the sample plane followed by a pixel-by-pixel scanning approach to record the image. In this study, a pinhole was aligned with one of the lobes of the fork shaped beam and the Airy diffraction pattern was used to illuminate biochemical samples. The diffracted light from the samples was captured using a NIR sensitive lensless camera. A rapid phase-retrieval algorithm was applied to the recorded intensity distributions to reconstruct the phase information. The preliminary results are promising to develop multimodal imaging capabilities at the IRM beamline of the Australian Synchrotron. [ABSTRACT FROM AUTHOR]

• A Light Origami Multi-Beam Interference – Digital Holographic Microscope (LOMBI-DHM) is proposed for live cell imaging that leverages single-shot acquisition and double field-of-view (FoV). • The concept of the proposed study to extend the FoV is based on the optical spatial multiplexing of two distinct regions of the object beam in a single hologram by adding a cube beam splitter in the path of the object beam. • The two distinct imaging regions corresponding to the two recorded FoVs, can be simultaneously retrieved during the reconstruction process. • The experimental findings of the proposed LOMBI-DHM point to a number of potential uses for this system, including optical metrology and biological imaging, with several advantages. In the field of scientific, industrial, and biological research, digital holographic microscopy (DHM) has established itself as a potential optical instrument due to its three-dimensional (3D) imaging capabilities and non-destructive nature. Like any imaging system, the field-of-view (FoV) of DHM is constrained by the image sensor's finite size. To address this challenge, in the present study, we propose the Light Origami Multi-Beam Interference (LOMBI)-DHM technique for live cell imaging that leverages single-shot acquisition and double FoV. The concept of the proposed study to extend the FoV is based on the optical spatial multiplexing of two distinct regions of the object beam by introducing a cube beam splitter in the path of the object beam. The beam splitter is angled so that it produces two object beams with different object information that are propagating in the same direction and collected within the area of the image sensor. The image sensor records a multiplexed digital hologram in a single-shot as a result of the interference of three beams: two object beams with different FoVs and one reference beam. The two distinct imaging regions corresponding to the two recorded FoVs, can be simultaneously retrieved during the reconstruction process. The experimental results of imaging different areas of a standard resolution target, microlens array, and living plant cells, are shown to demonstrate the capability of the proposed single-shot off-axis double FoV LOMBI-DHM. Furthermore, we dynamically monitor the time-lapse live-cell imaging of tobacco plant cells by the proposed system. [ABSTRACT FROM AUTHOR]

• A dual-wavelength high-speed digital holographic tomography system is developed. • The object beams from six different angles are simultaneously recorded by a single camera. • High-speed 3-D visualization inside the fluid at 2,000 frames per second has been achieved. • It is possible to track high-voltage discharge trajectories in three dimensions. Understanding and visualizing the intricate dynamics of rapidly moving fluids poses a fundamental challenge in the field of fluid mechanics. In this study, we present an innovative dual-wavelength high-speed digital holographic tomography system, poised to drive progress in the field of fluid dynamics research. This system has been meticulously crafted to enable the three-dimensional (3-D) visualization of rapidly moving and irregularly shaped airflow. To accomplish this, the system incorporates two lasers emitting different wavelengths, which effectively minimizes interference terms caused by the object beams in the off-axis multiplexing technique. Within this configuration, a single high-speed camera simultaneously captures the hologram generated by the interference between the reference and object beams from six different angles. In our experiment, the proposed system was utilized to achieve 3-D visualization of asymmetric airflow resulting from the high-voltage breakdown of air, capturing data at a rapid rate of 2,000 frames per second. Consequently, we successfully tracked the 3-D trajectory of the air breakdown phenomenon during discharge. The proposed system not only offers the ability to visualize asymmetric airflow in three dimensions but also has significant implications for gaining deeper insights into the behavior of fluids in dynamic and high-speed situations. [ABSTRACT FROM AUTHOR]

Fourier ptychography is a computational imaging techniques that combines various full-field coherent images acquired under varied illumination angles and combined to yield a angular spectrum with a large synthetic numerical aperture and non-interferometric phase information. We present here the implementation of this technique in a full-field soft x-ray microscope designed to emulate modern EUV lithography tools imaging conditions, and we show that this technique can be used for the study of EUV photomasks. The technique allows us to quantitatively characterize phase defects (predominant in EUV lithography), to study new mask designs made of phase structures, to study sub-resolution assist features and extend the resolution of the microscope down to 26-nm, correspond to the N1 technology node.

Phase contrast imaging is advantageous for mitigating radiation damage to samples, such as biological specimens. For imaging at nanometer or atomic resolution, the required flux on samples increases dramatically and can easily exceed the sample damage threshold. Coherent modulation imaging (CMI) can provide quantitative absorption and phase images of samples at diffraction-limited resolution with fast convergence. When used for radiation-sensitive samples, CMI experiments need to be conducted under low illumination flux for high resolution. Here, an algorithmic framework is proposed for CMI involving generalized alternating projection and total variation constraint. A five-to-ten-fold lower photon requirement can be achieved for near-field or far-field experiment dataset. The work would make CMI more applicable to the dynamics study of radiation-sensitive samples. [ABSTRACT FROM AUTHOR]

Commercially available carboxylated acrylonitrile butadiene latex (XNBR) was physically blended with natural rubber latex (NR) at varying blend ratios to investigate its effect on the mechanical properties and morphology. Methyl methacrylate grafted natural rubber latex (MG) was added to the latex blends as a third polymer to study whether it could enhance the mechanical properties of the latex blend films. It was found that the tensile strength of the blend films irrespective of composition decreased when the two latexes were blended as compared to the virgin latex films. The modulus 300 decreased while the elongation at break and tear strength of the blend films increased gradually as the ratio of NR increased in the blend films. It was found that the MG did not enhance the mechanical properties of the XNBR/NR blend films under the current experimental condition. AFM phase imaging analysis revealed enhanced polymer distribution and evidence of NR-MG-XNBR interactions. [ABSTRACT FROM AUTHOR]

The paper demonstrates a composite method of transport-of-intensity equation (TIE)-based phase imaging for broad range of spatial frequency recovery. In TIE-based phase imaging, with the increase in distance between imaging planes, the range of well-resolved spatial frequencies in the retrieved phase reduces. Therefore, we need smaller image separation to recover accurately the higher spatial frequencies. Similarly, to recover accurately the lower spatial frequencies, larger separation is required. A phase image recovered from intensity data captured at large defocus distance provides well-resolved low spatial frequencies at the expense of higher spatial frequencies. On the other hand, a phase image recovered from small defocus intensity data provides higher spatial frequency content at the cost of lower spatial frequencies. To overcome the difficulty of high and low spatial frequency content in a single phase image, a composite phase image can be reconstructed. A combined image with the high- and low-pass filtered phase images has been reconstructed which provide both higher and lower spatial frequency information. As a proof-of-concept, experiments have been carried out with two different samples; a micro-lens and USAF chart. [ABSTRACT FROM AUTHOR]

Phase imaging normally employs coherent a light source while an incoherent light source is not preferred due to its random wavefront. Another challenge for practical phase imaging is imaging through scattering media, which scatter the photons in a random manner and lead to seriously distorted images of speckles. Based on the convolutional neural network (CNN), this paper presents an approach for phase imaging through scattering media using an incoherent light source. A CNN was trained and utilized to reconstruct the target images from the captured images of speckles. Similarities of over 90% between the reconstructed images and their target images have been achieved. It was concluded that an incoherent light source can be used as an illumination source for scattering phase imaging with the assistance of deep learning technology. This phase imaging approach with an incoherent light source through scattering media can be used to record the refractive indices of transparent samples, which might lead to its application in biomedical imaging.

In this study, a novel identification method of white blood cells (WBCs) is proposed. Firstly, five phase characteristic parameters are introduced to characterize the detailed information used for WBCs identification. Secondly, a phase information acquisition device can simultaneously obtain two non-orthogonal phases of WBCs in batches, thereby improving the recognition accuracy. Finally, combining the threshold of the parameters and two phases in non-orthogonal directions, a label-free recognition process of WBCs subclasses based on phase features is established. Experimental results show that the method is feasible and provides new ideas and a technical basis for the analysis and classification of blood cells. [ABSTRACT FROM AUTHOR]

Twisted vector light beams (optical vortices) arise from a spiral modulation of the geometric (Pancharatnam–Berry) phase converting the light spin to the orbital angular momentum. The preferred geometric‐phase elements using liquid crystals and plasmonic metasurfaces realize this conversion by structuring their building blocks, i.e., precisely orienting individual crystal molecules or plasmonic nanoantennas. Here, an analogous mechanism is discovered in the spiral phase modulation of light reflected by dielectric spheres and first demonstrated in natural phenomena, namely in the rainbow formation. The spiral geometric phase is documented by holographic imaging of full circle primary and secondary rainbows created in the laboratory. The measurement uses a wide‐angle holographic camera (field of view ≈120°) taking time‐resolved self‐correlation holograms (300 ms). The holograms allow a quantitative restoration of the spiral geometric phase of light reflected from thousands of randomly falling water drops. The capability of individual drops to generate vector vortex beams under circularly polarized illumination is proven theoretically and demonstrated in experiments using glass microspheres. The spherical reflectors are discovered as simple generators of vector vortex beams and vortex arrays, inspiring novel geometric‐phase elements. [ABSTRACT FROM AUTHOR]

Purpose: Ex vivo imaging is a commonly used approach to investigate the biophysical mechanism of orientation‐dependent signal phase evolution in white matter. Yet, how phase measurements are influenced by the structural alteration in the tissue after formalin fixation is not fully understood. Here, we study the effects on magnetic susceptibility, microstructural compartmentalization, and chemical exchange measurement with a postmortem formalin‐fixed whole‐brain human tissue. Methods: A formalin‐fixed, postmortem human brain specimen was scanned with multiple orientations to the main magnetic field direction for robust bulk magnetic susceptibility measurement with conventional quantitative susceptibility imaging models. White matter samples were subsequently excised from the whole‐brain specimen and scanned in multiple rotations on an MRI scanner to measure the anisotropic magnetic susceptibility and microstructure‐related contributions in the signal phase and to validate the findings of the whole‐brain data. Results: The bulk isotropic magnetic susceptibility of ex vivo whole‐brain imaging is comparable to in vivo imaging, with noticeable enhanced nonsusceptibility contributions. The excised specimen experiment reveals that anisotropic magnetic susceptibility and compartmentalization phase effect were considerably reduced in the formalin‐fixed white matter specimens. Conclusions: Formalin‐fixed postmortem white matter exhibits comparable isotropic magnetic susceptibility to previous in vivo imaging findings. However, the measured phase and magnitude data of the fixed white matter tissue shows a significantly weaker orientation dependency and compartmentalization effect. Alternatives to formalin fixation are needed to better reproduce the in vivo microstructural effects in postmortem samples. [ABSTRACT FROM AUTHOR]

Phase loss is a typical problem in the optical domain, and optical detectors only measure the amplitude distribution of a signal without its phase. However, an optimal phase is desired in a variety of practical applications, such as optical metrology, nondestructive testing, and quantitative microscopy. Several methods have been proposed to quantitatively measure phase, among which interferometry is one of the most commonly used. An intensity interferometer has also been used to recover phase and enhance the phase difference measurement via the intensity correlation. In this paper, we present and examine another technique based on the Stokes correlation for enhancing phase measurement by a factor of two. The enhancement in phase measurement is accomplished through an evaluation of the correlation between two points of Stokes fluctuations of randomly scattered light and by recovering the enhanced phase of the object by using three-step phase shifting along with the Stokes correlations. This technique is expected to be useful for imaging and the experimental measurement of the phase of a weak signal.

A large number of carbon fiber reinforced polymers have been applied to aircraft and automobiles, and many nondestructive testing methods have been studied to detect their defects. Eddy current magneto-optical imaging nondestructive testing technology has been widely used in the detection of metal materials such as aircraft skin, but it usually requires a large excitation current and, at present, can only detect metal materials with high conductivity. In order to take full advantage of the innate benefits and efficiency of eddy current magneto-optic imaging and enable it to detect defects in carbon fiber reinforced polymers with weak conductivity, it is necessary to improve the magnetic field response of the eddy current magneto-optic imaging system and explore suitable excitation and detection methods. The scanning eddy current magneto-optical imaging nondestructive testing device built in this study has improved the magnetic field response of the system, and the eddy current magneto-optical phase imaging testing method has been proposed to detect the crack defects of carbon fiber reinforced polymers. The effectiveness of the method has been verified by simulation and experiment.

Fourier transform holography overcomes the phase recovery challenge through recording complex field information of the object in an interference pattern recorded at the far field, i.e., Fourier plane. Moreover, this geometry helps to reconstruct the complex field of the object from a single Fourier transform, which is an attractive feature for the numerical reconstruction of the digitally recorded hologram. In this paper, we present a nearly common path experimental design for recording a digital Fourier holographic hologram using a beam displacer, and recover the complex valued objects using the Fourier analysis. The performance of the system is experimentally examined for different objects.

We consider the application of a recently developed hyperspectral broadband phase retrieval (HSPhR) technique for spectrally varying object and modulation phase masks at 100 spectral components. The HSPhR method utilizes advanced techniques such as Spectral Proximity Operators and ADMM to retrieve complex-domain spectral components from multiple spectral observations. These techniques filter out noisy observations and strike a balance between noisy intensity observations and their predicted counterparts, resulting in accurate retrieval of the broadband hyperspectral phase even for low signal-to-noise ratio components. Both simulation and physical experiments have confirmed the effectiveness of this approach.

Tuning and probing electrical states of molybdenum disulfide (MoS2) with single-unit-cell thickness are attractive for next-generation nanoelectronics by virtue of unique electronic and optical attributes. In this work, we first demonstrated a plasmonic-based phase imaging of individual metal nanoparticles to directly visualize the characteristic switching of the electron-doping regime and near-complete suppression of the conductivity regime for an MoS2 monolayer by modulating potential. Intermediate states of electrical switching for the MoS2 monolayer are directly imaged by ultrasensitive phase variation of a single Au nanoparticle, which is attributable to the reversible switching between classical electromag-netic plasmonic coupling and quantum plasmonic coupling. This model can be operated as a logical inverter converting a logical signal 0-1 and as a universal logical NOR gate electronic directly imaged by plasmonic technique, potentially finding applications in novel nanoelectronics and optoelectronics. [ABSTRACT FROM AUTHOR]

In the context of bacteriophage (phage) therapy, there is an urgent need for a method permitting multiplexed, parallel phage susceptibility testing (PST) prior to the formulation of personalized phage cocktails for administration to patients suffering from antimicrobial-resistant bacterial infections. Methods based on surface plasmon resonance imaging (SPRi) and phase imaging were demonstrated as candidates for very rapid (<2 h) PST in the broth phase. Biosensing layers composed of arrays of phages 44AHJD, P68, and gh-1 were covalently immobilized on the surface of an SPRi prism and exposed to liquid culture of either Pseudomonas putida or methicillin-resistant Staphylococcus aureus (i.e., either the phages' host or non-host bacteria). Monitoring of reflectivity reveals susceptibility of the challenge bacteria to the immobilized phage strains. Investigation of phase imaging of lytic replication of gh-1 demonstrates PST at the single-cell scale, without requiring phage immobilization. SPRi sensorgrams show that on-target regions increase in reflectivity more slowly, stabilizing later and to a lower level compared to off-target regions. Phage susceptibility can be revealed in as little as 30 min in both the SPRi and phase imaging methods. [ABSTRACT FROM AUTHOR]

In this paper, we detail a phase-shift implementation in a rotated plane-parallel plate (PPP). Considering the phase-shifting digital holography application, we provide a more precise phase-shift estimation based on PPP thickness, rotation, and mutual inclination of reference and object wavefronts. We show that phase retardation uncertainty implemented by the rotated PPP in a simple configuration is less than the uncertainty of a traditionally used piezoelectric translator. Physical experiments on a phase test target verify the high quality of phase reconstruction. [ABSTRACT FROM AUTHOR]

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The Hartman wavefront sensor can be used for X-ray phase imaging with high angular resolution. The Hartmann sensor is able to retrieve both the phase and absorption from a single acquisition. The system calculates the shift in a series of apertures imaged with a detector with respect to their reference positions. In this article, the impact of the reference image on the final image quality is investigated using a laboratory setup. Deflection and absorption images of the same sample are compared using reference images acquired in air and in water. It can be easily coupled with tomographic setups to obtain 3D images of both phase and absorption. Tomographic images of a test sample are shown, where deflection images revealed details that were invisible in absorption. The findings reported in this paper can be used for the improvement of image reconstruction and for expanding the applications of X-ray phase imaging towards materials characterization and medical imaging. [ABSTRACT FROM AUTHOR]

Three-dimensional gradient echo (GRE) is the main workhorse sequence used for susceptibility weighted imaging (SWI), quantitative susceptibility mapping (QSM), and susceptibility tensor imaging (STI). Achieving optimal phase signal-to-noise ratio requires late echo times, thus necessitating a long repetition time (TR). Combined with the large encoding burden of whole-brain coverage with high resolution, this leads to increased scan time. Further, the dipole kernel relating the tissue phase to the underlying susceptibility distribution undersamples the frequency content of the susceptibility map. Scans at multiple head orientations along with calculation of susceptibility through multi-orientation sampling (COSMOS) are one way to effectively mitigate this issue. Additionally, STI requires a minimum of 6 head orientations to solve for the independent tensor elements in each voxel. The requirements of high-resolution imaging with long TR at multiple orientations substantially lengthen the acquisition of COSMOS and STI. The goal of this work is to dramatically speed up susceptibility mapping at multiple head orientations. We demonstrate highly efficient acquisition using 3D-GRE with Wave-CAIPI and dramatically reduce the acquisition time of these protocols. Using R=15-fold acceleration with Wave-CAIPI permits acquisition per head orientation in 90s at 1.1mm isotropic resolution, and 5:35min at 0.5mm isotropic resolution. Since Wave-CAIPI fully harnesses the 3D spatial encoding capability of receive arrays, the maximum g-factor noise amplification remains below 1.30 at 3T and 1.12 at 7T. This allows a 30-min exam for STI with 12 orientations, thus paving the way to its clinical application.

In Lamb wave-based structural health monitoring, amplitude damage imaging is commonly used because the defects feature can be easily amplified by summing all the response signals together. However, the grating and side lobes affect the imaging quality and blind areas further restrict the inspection area. Considering that the existing phase-based imaging algorithms are either unfit for dispersive Lamb wave or strict to many requirements to guarantee better performance, inspired by the absence of phase information in focusing phased array, a novel focusing phase imaging (FPI) method for Lamb wave phased array is developed. The main contribution of the paper is introducing the phase information to focusing phased array. By applying the inverse-dispersion effect to the excitation signals and the superposition operation, the energy can be focused at every inspection point. The phase damage index is constructed by directly measuring the degree of consistency and alignment of the instantaneous phases. The experiments for the circular and linear array under various excitation signals with multiple defects verify that the FPI is effective for both surface damage and through-hole damage. The proposed algorithm is superior for its ability in energy focusing for defects, the capability in suppression of grating and side lobes, strong anti-disturbance ability from boundary reflection, the nonexistence of imaging blind area, and its adaptability for various excitation parameters and array layout. [ABSTRACT FROM AUTHOR]

This article presents a 420-GHz phase imaging system designed in a 40-nm CMOS technology. It consists of a transmitter (TX), based on a multiplier chain, and a receiver (RX), based on a two-step IQ down-conversion. Those chips share an external, 17.5 GHz, reference to secure frequency synchronization between them. To increase the overall system signal-to-noise ratio (SNR), the TX is modulated with a low-frequency sine-wave signal, while a two-way LO power combining is implemented for the RX first mixer. Those techniques result in a measured TX effective isotropic radiated power (EIRP) of 10 dBm and RX noise figure (NF) of 27 dB, leading to the overall SNR of 52 dB (at a distance of 25 cm and a resolution bandwidth (RBW) of 100 kHz). Furthermore, the measured phase-detection root-mean-square (rms) $1\sigma $ precision is equal to 1.7° (on a 400 $\circ $ range, at a distance of 25 cm and processing time of 500 ns), which leads to 3.4- $\mu \text{m}$ range resolution. In addition, the system operation is illustrated in two imaging demonstrations, recognition of the printed text on paper and 3-D imaging. Those demonstrations illustrate the potential of the presented system and terahertz (THz) phase imaging in general. [ABSTRACT FROM AUTHOR]

Significance: Full-field optical coherence microscopy (FF-OCM) is a prevalent technique for backscattering and phase imaging with epi-detection. Traditional methods have two limitations: suboptimal utilization of functional information about the sample and complicated optical design with several moving parts for phase contrast., Aim: We report an OCM setup capable of generating dynamic intensity, phase, and pseudo-spectroscopic contrast with single-shot full-field video-rate imaging called bichromatic tetraphasic (BiTe) full-field OCM with no moving parts., Approach: BiTe OCM resourcefully uses the phase-shifting properties of anti-reflection (AR) coatings outside the rated bandwidths to create four unique phase shifts, which are detected with two emission filters for spectroscopic contrast., Results: BiTe OCM overcomes the disadvantages of previous FF-OCM setup techniques by capturing both the intensity and phase profiles without any artifacts or speckle noise for imaging scattering samples in three-dimensional (3D). BiTe OCM also utilizes the raw data effectively to generate three complementary contrasts: intensity, phase, and color. We demonstrate BiTe OCM to observe cellular dynamics, image live, and moving micro-animals in 3D, capture the spectroscopic hemodynamics of scattering tissues along with dynamic intensity and phase profiles, and image the microstructure of fall foliage with two different colors., Conclusions: BiTe OCM can maximize the information efficiency of FF-OCM while maintaining overall simplicity in design for quantitative, dynamic, and spectroscopic characterization of biological samples., (© 2024 The Authors.)

Purpose: Myelin has long been the target of neuroimaging research. However, most available techniques can only provide a voxel‐averaged estimate of myelin content. In the human brain, white matter fiber pathways connecting different brain areas and carrying different functions often cross each other in the same voxel. A measure that can differentiate the degree of myelination of crossing fibers would provide a more specific marker of myelination. Theory and Methods: One MRI signal property that is sensitive to myelin is the phase accumulation. This sensitivity is used by measuring the phase accumulation of the signal remaining after diffusion‐weighting, which is called diffusion‐prepared phase imaging (DIPPI). Including diffusion‐weighting before estimating the phase accumulation has two distinct advantages for estimating the degree of myelination: (1) It increases the relative contribution of intra‐axonal water, whose phase is related linearly to the thickness of the surrounding myelin (in particular the log g‐ratio); and (2) it gives directional information, which can be used to distinguish between crossing fibers. Here the DIPPI sequence is described, an approach is proposed to estimate the log g‐ratio, and simulations are used and DIPPI data acquired in an isotropic phantom to quantify other sources of phase accumulation. Results: The expected bias is estimated in the log g‐ratio for reasonable in vivo acquisition parameters caused by eddy currents (~4%‐10%), remaining extra‐axonal signal (~15%), and gradients in the bulk off‐resonance field (<10% for most of the brain). Conclusion: This new sequence may provide a g‐ratio estimate per fiber population crossing within a voxel. [ABSTRACT FROM AUTHOR]

PurposeTo introduce the wave-CAIPI (controlled aliasing in parallel imaging) acquisition and reconstruction technique for highly accelerated 3D imaging with negligible g-factor and artifact penalties.MethodsThe wave-CAIPI 3D acquisition involves playing sinusoidal gy and gz gradients during the readout of each kx encoding line while modifying the 3D phase encoding strategy to incur interslice shifts as in 2D-CAIPI acquisitions. The resulting acquisition spreads the aliasing evenly in all spatial directions, thereby taking full advantage of 3D coil sensitivity distribution. By expressing the voxel spreading effect as a convolution in image space, an efficient reconstruction scheme that does not require data gridding is proposed. Rapid acquisition and high-quality image reconstruction with wave-CAIPI is demonstrated for high-resolution magnitude and phase imaging and quantitative susceptibility mapping.ResultsWave-CAIPI enables full-brain gradient echo acquisition at 1 mm isotropic voxel size and R = 3 × 3 acceleration with maximum g-factors of 1.08 at 3T and 1.05 at 7T. Relative to the other advanced Cartesian encoding strategies (2D-CAIPI and bunched phase encoding) wave-CAIPI yields up to two-fold reduction in maximum g-factor for nine-fold acceleration at both field strengths.ConclusionWave-CAIPI allows highly accelerated 3D acquisitions with low artifact and negligible g-factor penalties, and may facilitate clinical application of high-resolution volumetric imaging.

Phase imaging of biochemical samples has been demonstrated for the first time at the Infrared Microspectroscopy (IRM) beamline of the Australian Synchrotron using the usually discarded near-IR (NIR) region of the synchrotron-IR beam. The synchrotron-IR beam at the Australian Synchrotron IRM beamline has a unique fork shaped intensity distribution as a result of the gold coated extraction mirror shape, which includes a central slit for rejection of the intense X-ray beam. The resulting beam configuration makes any imaging task challenging. For intensity imaging, the fork shaped beam is usually tightly focused to a point on the sample plane followed by a pixel-by-pixel scanning approach to record the image. In this study, a pinhole was aligned with one of the lobes of the fork shaped beam and the Airy diffraction pattern was used to illuminate biochemical samples. The diffracted light from the samples was captured using a NIR sensitive lensless camera. A rapid phase-retrieval algorithm was applied to the recorded intensity distributions to reconstruct the phase information. The preliminary results are promising to develop multimodal imaging capabilities at the IRM beamline of the Australian Synchrotron.

Phase contrast imaging is advantageous for mitigating radiation damage to samples, such as biological specimens. For imaging at nanometer or atomic resolution, the required flux on samples increases dramatically and can easily exceed the sample damage threshold. Coherent modulation imaging (CMI) can provide quantitative absorption and phase images of samples at diffraction-limited resolution with fast convergence. When used for radiation-sensitive samples, CMI experiments need to be conducted under low illumination flux for high resolution. Here, an algorithmic framework is proposed for CMI involving generalized alternating projection and total variation constraint. A five-to-ten-fold lower photon requirement can be achieved for near-field or far-field experiment dataset. The work would make CMI more applicable to the dynamics study of radiation-sensitive samples.

Integrated multimodal cross-sectional or volumetric imaging techniques give us fruitful information to understand the behavior or status of target objects such as biological samples. Most of the reported systems for this purpose are either time consuming due to scanning or use additional reference beams such as in interferometry. Therefore, fast, simple, highly efficient, and powerful multimodal imaging systems that can perform cross-sectional imaging with simple algorithms are worth to be investigated. In this paper, a multimodal technique for cross-sectional quantitative phase and fluorescence imaging with computational microscopy is presented. We combine cross-sectional fluorescence and quantitative phase imaging by using the transport of intensity equation (TIE) and numerical wave propagation. The amplitude and phase of the fluorescence light wave with partially spatial coherence are obtained from three defocused intensity patterns. The proposed hybrid imaging system is simple, compact, and non-iterative. We present experimental results of microbeads and fluorescent protein-labeled living cells of the moss Physcomitrella patens to demonstrate the performance of the proposed imaging system. [ABSTRACT FROM AUTHOR]

The performance of single-shot off-axis digital holographic microscopy (DHM) is determined by the optimum utilization of the space-bandwidth product and by the contrast of the recorded digital hologram. While the former can be easily achieved through an afocal-telecentric DHM, the finding in nature of samples with non-homogeneous transmittance leads to the recording of digital holograms with contrast ranging from zero to unity. In this work, the effect of the sample transmittance and the bit depth of the digital camera on the performance of quantitative phase imaging in DHM is studied. A theoretical model that links the contrast of the recorded interference fringes, in a transmission-mode DHM, to the bit depth of the digital camera is derived. The model is implemented in an open-source visual script for easy consultation and predicts that, when recorded with a 16-bit-depth camera, digital holograms of samples that have regions with transmittance below 1% can be successfully processed to render reliable phase information. The theoretical and computer-modeled results are validated with experimental results from a complex sample of the mouth of a honeybee and from endothelial cells slide. [ABSTRACT FROM AUTHOR]

Refractive index is a fundamental optical property of powder that is used as an important input in light scattering measurements of the size distribution and diffuse reflectance spectroscopy measurements of the absorption and scattering coefficients. In this work, we demonstrate a method that combines index matching with phase imaging to determine the refractive index of complex powder particles at high accuracy without relying on any assumptions. Index matching is robust, but the accuracy is not high by relying on ocular observation of the interface. Phase imaging using interferometry improves the accuracy of determining the match by an order of magnitude. Using the proposed method, we determine the refractive index of four types of pharmaceutical powder in the short-wave infrared range of 1100–1650 nm. [Display omitted] • Refractive index measurement for complex, arbitrary microparticles. • Index matching with an order-of-magnitude higher accuracy. • Refractive index of pharmaceutical powders in the short-wave infrared range. [ABSTRACT FROM AUTHOR]

As a non-interferometric method, the transport of intensity equation (TIE) method suits for quantitative phase imaging with the commercial microscope platform, especially those higher order TIE approaches which can realize precise phase retrieval by eliminating undesired higher order derivatives are widely used. However, these approaches are mostly adopted separately without considering their phase retrieval precision in various noise levels. In this paper, we first compared these classical higher order TIE approaches through theoretical analysis, numerical simulations, and experiments. Then, based on the quantitative comparisons mainly focusing on their phase retrieval accuracy and noise suppression capability, we determine the application scope corresponding to different noise levels of each higher order TIE approach. Finally, in order to deal with different noisy cases, we design the hybrid higher order TIE application, in which the specific higher order TIE approach is selected for phase retrieval according to the precise noise estimation, and the performance of the hybrid higher order TIE application is tested by both the numerical simulations and the experiments, proving it can perform high-quality phase imaging by balancing the tradeoff between the phase retrieval accuracy and the noise influence. The paper not only provides a systematic reference for analysis and comparisons on different higher order TIE approaches, but also proposes the hybrid application for noise adaptive phase imaging, which can be a potential tool in biological observations and medical diagnostics.

Neutron imaging based on a compact Talbot–Lau interferometer was demonstrated using the RIKEN accelerator-driven compact neutron source (RANS). A compact Talbot–Lau interferometer consisting of gadolinium absorption gratings and a silicon phase grating was constructed and connected to the RANS. Because of pulsed thermal neutrons from the RANS and a position-sensitive detector equipped with time-of-flight (TOF) analysis, moiré interference patterns generated using the interferometer were extracted at a TOF range around the design wavelength (2.37 Å) optimal for the interferometer. Differential phase and scattering images of the metal rod samples were obtained through phase-stepping measurements with the interferometer. This demonstrates the feasibility of neutron phase imaging using a compact neutron facility and the potential for flexible and unique applications for nondestructive evaluation.