Object Plane Research Articles

Terahertz Nonlinear Ghost Imaging via Plane Decomposition: Toward Near-Field Micro-Volumetry.

Terahertz time-domain imaging targets the reconstruction of the full electromagnetic morphology of an object. In this spectral range, the near-field propagation strongly affects the information in the space-time domain in items with microscopic features. While this often represents a challenge, as the information needs to be disentangled to obtain high image fidelity, here, we show that such a phenomenon can enable three-dimensional microscopy. Specifically, we investigate the capability of the time-resolved nonlinear ghost imaging methodology to implement field-sensitive micro-volumetry by plane decomposition. We leverage the temporally resolved, field-sensitive detection to "refocus" an image plane at an arbitrary distance from the source, which defines the near-field condition, and within a microscopic sample. Since space-time coupling rapidly evolves and diffuses within subwavelength length scales, our technique can separate and discriminate the information originating from different planes at different depths. Our approach is particularly suitable for objects with sparse micrometric details. Building upon this principle, we demonstrate complex, time-domain volumetry resolving internal object planes with subwavelength resolution, discussing the range of applicability of our technique.

Centroid-based graph matching networks for planar object tracking

Centroid-based graph matching networks for planar object tracking

Image fusion of multi-vision system with one high resolution image for the measurement of long distance

The mutual restriction between angle detection accuracy and spatial resolution of image will restrict the detection of long distance by multi-vision system. One higher resolution image of a multi-vision system can be used to improve the resolution of the images of each camera. In order to enhance the fusion effect of planar objects, a novel method has been proposed for dealing with high-resolution images and tested for applications. As an example, an image fusion for the images captured by the combining optical system of camera arrays and the synthetic aperture is studied. Both of the simulation and experiment shows that the proposed method is simple and accuracy.

On the relationship between the properties of planar structures of non-ionic surfactants and their vesicular analogues – Niosomes

In recent years, the study of niosomes as nanocarriers alternative to liposomes has received increasing attention. In contrast to well-studied liposome membranes, many aspects of the behavior of analogous niosome bilayers have not been studied. This paper considers one of these aspects related to the communication between the physicochemical properties of planar and vesicular objects. We present the first results of comparative studies of Langmuir monolayers of binary and ternary (with cholesterol) mixtures of non-ionic surfactants based on sorbitan esters and niosomal structures assembled from the same materials. The Thin-Film Hydration (TFH) method in the gentle shaking version was used to produce the particles of large sizes, while small unilamellar high quality vesicles with a unimodal distribution of particles were prepared by TFH using ultrasonic treatment and extrusion. An analysis of the structural organization and phase state of monolayers based on compression isotherms and supplemented by thermodynamic calculations, as well as the results of determining the particle morphology, polarity and microviscosity of niosome shells, made it possible to obtain fundamental data on the intermolecular interactions of the components and their packing in shells and to relate these data to the properties of niosomes. This relationship can be used to optimize the composition of niosome membranes and predict the behavior of these vesicular systems. It was shown that cholesterol excess creates regions of bilayers with increased rigidity (like “lipid rafts”), which hinders the process of folding film fragments into small niosomes.

Sidelobe suppression in structured light sheet fluorescence microscopy by the superposition of two light sheets.

Light sheet microscopy has emerged as a powerful technique for three-dimensional and long-term vivo imaging within neuroscience and developmental biology. A light sheet illumination with structured light fields allows a better tradeoff between the field of view and axial resolution but suffers from strong side lobes. Here, we propose a method of producing structured light sheet illumination with suppressed side lobes by applying the superposition of two light sheets. The side lobe suppression results from the destructive interference between the side lobes and constructive interference between the main lobe of the two light sheets. In the proposed method, the incident light pattern in the rear pupil plane of the illumination objective is a combination of the incident light line beams required for the generation of the two interfering light sheets. We present a fast and simple calculation method to determine the incident light pattern in the rear pupil plane. Simulation results demonstrate the effectiveness of the proposed sidelobe suppression method for double-line light sheet, four-line light sheet, as well as line Bessel sheet. In particular, an 81% decrease in the relative side lobe energy can be achieved in case of double-line light sheet with an almost nonchanging propagation length. We show a way of using combined incident light patterns to generate structured light sheets with interference-resulted side lobe suppression, which is straightforward in design and with advantages of improved imaging performance.

Reducing crosstalk of a multi-plane holographic display by the time-multiplexing stochastic gradient descent.

Multi-plane reconstruction is essential for realizing a holographic three-dimensional (3D) display. One fundamental issue in conventional multi-plane Gerchberg-Saxton (GS) algorithm is the inter-plane crosstalk, mainly caused by the neglect of other planes' interference in the process of amplitude replacement at each object plane. In this paper, we proposed the time-multiplexing stochastic gradient descent (TM-SGD) optimization algorithm to reduce the multi-plane reconstruction crosstalk. First, the global optimization feature of stochastic gradient descent (SGD) was utilized to reduce the inter-plane crosstalk. However, the crosstalk optimization effect would degrade as the number of object planes increases, due to the imbalance between input and output information. Thus, we further introduced the time-multiplexing strategy into both the iteration and reconstruction process of multi-plane SGD to increase input information. In TM-SGD, multiple sub-holograms are obtained through multi-loop iteration and then sequentially refreshed on spatial light modulator (SLM). The optimization condition between the holograms and the object planes converts from one-to-many to many-to-many, improving the optimization of inter-plane crosstalk. During the persistence of vision, multiple sub-hologram jointly reconstruct the crosstalk-free multi-plane images. Through simulation and experiment, we confirmed that TM-SGD could effectively reduce the inter-plane crosstalk and improve image quality.The proposed TM-SGD-based holographic display has wide applications in tomographic 3D visualization for biology, medical science, and engineering design, which need to reconstruct multiple independent tomographic images without inter-plane crosstalk.

Aberration-free warp projection on a horopter screen using freeform holographic optical elements.

A horopter screen has been popularly studied since its curvature reduces the parallax between two eyes and the immersive displays with a horopter-curved screen are regarded to provide vivid impression of depth and stereopsis. But, the projection on a horopter screen causes some practical problems that the image is hard to be focused on the entire screen and its magnification is partially different. An aberration-free warp projection has a great potential to solve these problems, which changes the optical path from an object plane to an image plane. Since the variation of the curvature is severe in the horopter screen, a freeform optical element is required for an aberration-free warp projection. In comparison with the traditional fabrication method, the hologram printer has the advantage of rapidly manufacturing free-form optical devices by recording the desired wavefront phase on the holographic medium. In this paper, for a given arbitrary horopter screen, the aberration-free warp projection is implemented with the freeform holographic optical elements (HOEs) fabricated by our tailor-made hologram printer. We experimentally demonstrate that the distortion and defocus aberration are effectively corrected.

The multiplanar imaging microscope with a laser induced thermal lens: A practical case study

The article presents the operation of the first in the world fully functional multi-planar, ready-to-use bright-field microscope equipped with a laser induced thermal lens. Also, for the first time the imaging capabilities of a thermal lens formed in a polymer sample are presented. The microscope objective and the thermal lens are used in a multifocal configuration which allows recording in the same plane the images of objects belonging to different object planes, separated by a distance that exceeds significantly the objective depth-of-field. The thermal lens kinetics response to laser on/off switching as well as the effect of the geometry of illumination light on the microscope multiplanar imaging capability are shown. Multiplanar exemplary images are presented as well.

High-energy X-ray micro-laminography to visualize microstructures in dense planar objects.

High-energy X-ray micro-laminography has been developed to observe inner- and near-surface structures in dense planar objects that are not suitable for observation by X-ray micro-tomography. A multilayer-monochromator-based high-intensity X-ray beam with energy of 110 keV was used for high-energy and high-resolution laminographic observations. As a demonstration of high-energy X-ray micro-laminography for observing dense planar objects, a compressed fossil cockroach on a planar matrix surface was analyzed with effective pixel sizes of 12.4 µm and 4.22 µm for wide field of view and high-resolution observations, respectively. In this analysis, the near-surface structure was clearly observed without undesired X-ray refraction-based artifacts from outside of the region of interest, a problem typical in tomographic observations. Another demonstration visualized fossil inclusions in a planar matrix. Micro-scale features of a gastropod shell and micro-fossil inclusions in the surrounding matrix were clearly visualized. When observing local structures in the dense planar object with X-ray micro-laminography, the penetrating path length in the surrounding matrix can be shortened. This is a significant advantage of X-ray micro-laminography where desired signals generated at the region of interest including optimal X-ray refraction effectively contribute to image formation without being disturbed by undesired interactions in the thick and dense surrounding matrix. Therefore, X-ray micro-laminography allows recognition of the local fine structures and slight difference in the image contrast of planar objects undetectable in a tomographic observation.

Image-Based Visual Impedance Force Control for Contact Aerial Manipulation

In this paper, an image-based impedance control strategy for force tracking of an unmanned aerial manipulator (UAM) is presented. Firstly, image features with nice decoupling characteristics are designed and the relationship between the camera motion and the image features is derived. Then, a two-stage strategy is proposed to achieve force tracking of the UAM on a planar object in an arbitrary pose. The first stage drives the end-effector perpendicular to the object’s planer surface by pure visual servoing. To achieve force tracking under the visual guidance, an adaptive visual impedance control method which adjusts the target stiffness according to the force tracking error and the visual feature error is proposed in the second stage. The closed-loop system is proved asymptotically stable by means of Lyapunov analysis. Further, the stability in free flight phase of the stage two is also analyzed and ensured. Finally, experiments were carried out including a whiteboard cleaning task in different poses. The experimental results illustrate the validity and effectiveness of the proposed approach. Note to Practitioners—This work is motivated by the contact force tracking problem of an unmanned aerial manipulator (UAM) without the position measurement. In recent years, impedance control is widely used in force tracking problems. However, position measurement is needed both for the robot and the object in most studies. To generate desired force under visual guidance, image-based visual servoing is combined with a novel impedance controller with variable stiffness. The idea is intuitive. For a human in contact with a wall, the contact force is controlled by adjusting his arm stiffness, which means the stiffness is adapted to the difference between the desired and actual contact force. Furthermore, the stiffness is also adapted to the visual tracking error, removing the assumption that no tracking error is in the inner loop of the impedance controller in the previous works. The proposed strategy is a promising solution for real applications and is validated by a board cleaning experiment in this paper.

In situ preparation of ultrastable and flexible BA2PbBr4 nanocrystal films for X-ray imaging

The ultrastable and flexible BA2PbBr4 NC@PMMA film, which was fabricated by using an in situ fabrication method, has achieved X-ray imaging for planar and nonplanar objects with a high spatial resolution of 5.5 lp mm−1.

Investigation of Modeling and Control for Transporting and Positioning Planar Object on Contactless Air Conveyor

Investigation of Modeling and Control for Transporting and Positioning Planar Object on Contactless Air Conveyor

Tomographic incoherent holography for microscale X-ray source

At present, in the experiment on inertial confinement fusion (ICF), no single imaging diagnosis of the black cavity plasma or the implosion target region can distinguish the emission intensity information in the depth direction, that is, the images acquired by the detector are intensity integral along the detection direction. In this paper, a tomographic imaging method using incoherent holography for microscale X-ray source is introduced. The incoherent holographic imaging technology has an imaging mechanism that encodes and compresses the three-dimensional space information of the light source into a two-dimensional hologram. In the theoretical part, we examine the imaging mechanism of incoherent holographic tomography. Then the compress sensing model which is appropriate for this incoherent tomography is investigated. Combined with the hologram reconstruction algorithm based on compress sensing, the two-dimensional distributions of light intensity at different object distances along the detection direction can be recovered from the two-dimensional hologram. In order to verify the feasibility of this imaging scheme, we simulate the incoherent holographic imaging process of a light source with an axial length of 16 mm, and obtain the tomography light intensity distribution result with a spacing of 4 mm by reconstructing the corresponding incoherent hologram through using the backpropagation algorithms, Wiener filtering algorithm, and compress sensing algorithm. All reconstruction methods mentioned above can recover the corresponding letter light source at a certain object distance, indicating the potential of incoherent holographic technology for three-dimensional imaging. For the backpropagation reconstruction image, there is a large amount of series noise at the edge of the light source signal, which affects signal recognition in practical applications. Although the Wiener filtering algorithm can recognize the image signal to some extent, the low contrast of the reconstructed image results in the distribution of target source strength mixed with background noise. Compared with the algorithm based on the Wiener filtering and backpropagation, compress sensing theory provides a more professional technique for the ill-condition problem. Results from compress sensing reconstruction show that the crosstalk noise is significantly reduced, and the intensity distribution on the objective plane of the light source is basically concentrated in the signal area. The peak-signal-to-noise ratio of reconstructed image is continuously optimized as the number of iterations increases. Besides, the axial and horizontal resolution caused by the innermost ring radius of Fresnel zone plate are also analyzed, indicating that a shorter innermost ring radius can improve the horizontal resolution, bur reduce the axial resolution.

A self-adjusting and modular supervisory control algorithm for planar dexterous manipulation

Many applications require precise handling and manipulation of delicate objects. In some cases, the object must be transported to a new location following a strict travel path including time-related constraints. This paper presents a self-adjusting modular control algorithm for dexterous manipulation of planar objects using multiple manipulators with precise path and timing deliveries. The popular caging approach is simple, and usually effective when manipulating objects with multiple devices but can fail following complex paths with orientation adjustments under time-critical tracking requirements. The proposed approach exploits the dynamics of the object in real-time using tracking control and allocates the force that needs to be applied by each manipulator based on their current position around the object to maximize their capability to push in the direction of the contact angle. The new algorithm is self-adjusting and modular; It can adjust its force allocation according to configuration changes during operation, and manipulators execute the same algorithm regardless of their number. The advantages of the new approach are successfully demonstrated both with simulations and testbed experiments, including orientation tracking, which is not typically featured with the caging approach. Conditions to check when the new algorithm is most effective are also analyzed. The closed-loop stability and performance of the new algorithm are also studied and necessary conditions are identified.

Multiple airy beams light-sheet fluorescence microscopy

Light-sheet fluorescence microscopy (LSFM) is a kind of volumetric imaging methodology suited for long term living specimens at high temporal-spatial resolution. A single Airy beam (SAB) light-sheet can extend the field of view of Light-sheet fluorescence microscopy benefiting from its non-diffracting nature, but at the cost of out-of-focus background and low imaging contrast caused by side lobes illumination. Here, we propose a method to generate a sort of multiple Airy beams (MAB), which are linearly superimposed of multiple single Airy beams with different scale factors. Compared to the SAB light-sheet, the energy of the multiple Airy beams light-sheet is more concentrated on the focal plane of the detection objective, which can improve the imaging contrast and decrease the photodamage effect. Furthermore, we combined the complementary beam subtraction (CBS) strategy to increase the axial resolution, termed as multiple Airy beams-complementary beam subtraction method, which enables the axial resolution of 1.2 μm while keeping the field of view of 450 μm × 450 μm. The effectiveness of the method is demonstrated by imaging of fluorescent beads and aspergillus conidiophores.

Signal strength and integrated intensity in confocal and image scanning microscopy.

The properties of signal strength and integrated intensity in a scanned imaging system are reviewed. These properties are especially applied to confocal imaging systems, including image scanning microscopy. The integrated intensity, equal to the image of a uniform planar (sheet) object, rather than the peak of the point spread function, is a measure of the flux in an image. Analytic expressions are presented for the intensity in the detector plane for a uniform volume object, and for the resulting background. The variation in the integrated intensity with defocus for an offset point detector is presented. This axial fingerprint is independent of any pixel reassignment. The intensity in the detector plane is shown to contain the defocus information, and simple processing of the recorded data can improve optical sectioning and background rejection.

Quantum ghost imaging of a transparent polarisation sensitive phase pattern

A transparent polarisation sensitive phase pattern exhibits a position and polarisation dependent phase shift of transmitted light and it represents a unitary transformation. A quantum ghost image of this pattern is produced with hyper-entangled photons consisting of Einstein-Podolsky-Rosen (EPR) and polarisation entanglement. In quantum ghost imaging, a single photon interacts with the pattern and is detected by a stationary detector and a non-interacting photon is imaged on a coincidence camera. EPR entanglement manifests spatial correlations between an object plane and a ghost image plane, whereas a polarisation dependent phase shift exhibited by the pattern is detected with polarisation entanglement. In this quantum ghost imaging, the which-position-polarisation information of a photon interacting with the pattern is not present in the experiment. A quantum ghost image is constructed by measuring correlations of the polarisation-momentum of an interacting photon with polarisation-position of a non-interacting photon. The experiment is performed with a coincidence single photon detection camera, where a non-interacting photon travels a long optical path length of 17.83 m from source to camera and a pattern is positioned at an optical distance of 19.16 m from the camera.

Object-Based Learning Rocks! Integrating Digital Solutions into Geology Practicum

Over several years, the authors have pursued technology solutions to the difficult arena of moving geology practicum work into the online space (e.g., Tetley and Daczko, 2014). Through a partnership of teaching academics with professional staff trained in digitisation and software development, the authors have now solved the problem of verisimilitude and utility and opened a raft of future opportunities including a smooth and seamless transition to online teaching when presented with recent pandemic lockdowns. “Teaching geology with digital tools advances students’ learning experience by providing access to high-quality outcrops, enhancing visualization of 3D geological structures and improving data integration.” (Senger et al., 2021) Our solution required innovation on several fronts. Firstly, 3D digitisation and gigapixel imaging processes and methods were tried, evaluated, abandoned and refined until an ideal solution was developed that could actually replace the physical rock hand samples. Secondly, software platform development and integration was required. We utilised a custom developed 3D platform (Pedestal 3D) and also developed a bespoke platform for virtual petrographic microscopy (ImageMatrix). Finally, as “the organisation, logistics and relevance of an OBL session is critical to its efficacy” (Chatterjee and Hannan, 2016), all of this needed significant pedagogical underpinning and integration to ensure learning and outcomes were not impacted by the technology shift. We found that generally, digital resources allow for and encourage much more practice of the professional skills required for identification of minerals. “Most professional geoscientists spend much of their day in front of work-stations, interpreting or modelling digital data, in two or three dimensions.” (Bond and Wightman, 2012) so this mode of delivery is a naturally suited authentic task. On top of that, digital pre-lab work prepares students for being confronted with actual samples. Being able to digitally annotate the samples allowed for a virtual “guide on the side” pedagogy to allow for clarity of tasks and identification of specific object traits that are difficult in the traditional practical setting. The three main areas of impact were in Workshops, Field Trips and general Practicum. The specific mineral identification workshops were extended in a blended sense pre-COVID-19 and then seamlessly moved to online when required during the pandemic without any further development. Geological fieldwork traditionally has several core functions. “These include the determination of the geographical location of observation points, the description of outcrops, the macroscopic description of rocks, the detection of lithological boundaries, the spatial fixation of planar and linear objects (folds, joints, faults, linear position of minerals, etc.).” (Bubaniak et al., 2020) To respond to this digitally, a landmark yearly field trip in the program was developed into a fully online virtual field trip. The general practicum across the course was enabled to be taught in an online only mode which had never been possible before. We found that grade distribution did not suffer during the COVID-19 period which demonstrates that this mode of Digital Object-Based Learning is as good as traditional approaches to teaching. Although not originally intended, coursework could now also be offered fully online which opens a range of possibilities moving forward.

An Analytical Solution to Steady-State Temperature Field in the FSPR Method Considering Different Soil Freezing Points

Taking the freeze-sealing pipe roof method (FSPR) adopted in the Gongbei Tunnel project as the background, this study develops a simplified calculation model by considering different soil freezing points, tube layout, and site conditions. The analytical solution of the linear single row tubes is then used to formulate the analytical solution of the freezing temperature field of two kinds of linear single row tubes, with equal spacing in the image plane. This is achieved through conformal mapping and the variable separation method. Finally, the analytical solution to the steady-state temperature field of FSPR in the object plane is obtained. The numerical solutions of common freezing parameters in freezing engineering are analyzed to evaluate the accuracy of the analytical solution, and the influence of parameter differences on the freezing temperature field are also discussed, to provide a theoretical reference for popularization and application of similar construction methods.

An interference iterative reconstruction algorithm based on a single off-axis digital hologram

Compared with in-line digital holography, off-axis digital holography can be used to image more kinds of objects without the limitation of weak phase and sparsity, but the resolution is lower. In this paper, we put forward a high-resolution iterative reconstruction algorithm for off-axis holography which requires only the recording of a single off-axis hologram. Interference and inverse interference processes are used to extract the object wave from the off-axis hologram. A frequency domain filter with increasing radius is used to improve the competitive advantage of low frequency information in the early iterations, while retaining the high frequency information. The constraints of total variation and positive absorption are implemented at the object plane to enhance the robustness of the algorithm. Numerical simulations and experiments show that the resolution of our method is higher than traditional off-axis digital holography. In addition, it is suitable for phase image when the object has a strong phase fluctuation, as well as for imaging dynamical objects.