Object Beam Research Articles

Photobiomodulation improves functional recovery after mild traumatic brain injury

AbstractMild traumatic brain injury (mTBI) is a common consequence of head injury but there are no recognized interventions to promote recovery of the brain. We previously showed that photobiomodulation (PBM) significantly reduced the number of apoptotic cells in adult rat hippocampal organotypic slice cultures. In this study, we first optimized PBM delivery parameters for use in mTBI, conducting cadaveric studies to calibrate 660 and 810 nm lasers for transcutaneous delivery of PBM to the cortical surface. We then used an in vivo weight drop mTBI model in adult rats and delivered daily optimized doses of 660, 810 nm, or combined 660/810 nm PBM. Functional recovery was assessed using novel object recognition (NOR) and beam balance tests, whilst histology and immunohistochemistry were used to assess the mTBI neuropathology. We found that PBM at 810, 660 nm, or 810/660 nm all significantly improved both NOR and beam balance performance, with 810 nm PBM having the greatest effects. Histology demonstrated no overt structural damage in the brain after mTBI, however, immunohistochemistry using brain sections showed significantly reduced activation of both CD11b+ microglia and glial fibrillary acidic protein (GFAP)+ astrocytes at 3 days post‐injury. Significantly reduced cortical localization of the apoptosis marker, cleaved caspase‐3, and modest reductions in extracellular matrix deposition after PBM treatment, limited to choroid plexus and periventricular areas were also observed. Our results demonstrate that 810 nm PBM optimally improved functional outcomes after mTBI, reduced markers associated with apoptosis and astrocyte/microglial activation, and thus may be useful as a potential regenerative therapy.

X-ray ghost imaging with a specially developed beam splitter.

X-ray ghost imaging with a crystal beam splitter has advantages in highly efficient imaging due to the simultaneous acquisition of signals from both the object beam and reference beam. However, beam splitting with a large field of view, uniform distribution and high correlation has been a great challenge up to now. Therefore, a dedicated beam splitter has been developed by optimizing the optical layout of a synchrotron radiation beamline and the fabrication process of a Laue crystal. A large field of view, consistent size, uniform intensity distribution and high correlation were obtained simultaneously for the two split beams. Modulated by a piece of copper foam upstream of the splitter, a correlation of 92% between the speckle fields of the object and reference beam and a Glauber function of 1.25 were achieved. Taking advantage of synthetic aperture X-ray ghost imaging (SAXGI), a circuit board of size 880 × 330 pixels was successfully imaged with high fidelity. In addition, even though 16 measurements corresponding to a sampling rate of 1% in SAXGI were used for image reconstruction, the skeleton structure of the circuit board can still be determined. In conclusion, the specially developed beam splitter is applicable for the efficient implementation of X-ray ghost imaging.

Computational vibration mitigation using phase interpolation in digital holographic microscopy for overlay metrology

Digital holographic microscopy retrieves amplitude and phase information of an image which allows us to computationally correct for imperfections in the imaging optics. However, digital holographic microscopy is an interferometric technique that is inherently sensitive to undesired phase variations between object and reference beam. These phase variations lower the fringe contrast if they are integrated over a finite exposure time which leads to a reduced amplitude of the retrieved image. This results in significant errors in applications that rely on a stable and accurate amplitude measurement, such as optical overlay metrology in the semiconductor industry. We present experimental results on a computational vibration mitigation method for the application of overlay metrology using phase interpolation between a sequence of measured holograms and demonstrate its capability to improve metrology precision in an overlay metrology application that uses digital holographic microscopy.

Compact common-path polarization holography for measurement of the Jones matrix of polarization-sensitive materials

A compact common-path off-axis digital holographic imaging method is proposed utilizing polarization-angular-multiplexing for Jones matrix measurement. Our method employs a common-path off-axis configuration to capture multiplexed off-axis interferograms generated by orthogonally polarized object beams and a reference beam on a monochrome CCD camera. The modulation of the fringe direction is achieved by two homemade retro-reflector mirrors, allowing for the retrieval of the Jones matrix distribution of transparent specimens through a matrix-division algorithm. The stable common-path design and the expansive camera field of view facilitate the extraction of spatially resolved Jones matrix parameters. The feasibility of this method was validated through experiments involving standard objects and polarization-sensitive materials, conducted at both general and microscopic scales. Our system completed polarization imaging of cancerous tissues, unequivocally demonstrating its extraordinary potential in medical pathology diagnostics.

Single shot point-diffraction interferometer by a plate beamsplitter

A single shot point-diffraction interferometer (PDI) is proposed in this paper, in which the object beam is split into two copies by means of a beamsplitting module consisting of one plate beamsplitter and one mirror. One of the reflected beams is spatially filtered as a reference beam by one pinhole array in the spectral plane. The split two beams share almost the same path, and by adjusting the inclined angle of the plate beamsplitter, the carrier frequency and legibility of the interferogram can be modulated easily. Moreover, the contrast of the interferogram can be adjusted by changing different plate beamsplitters. Compared to conventional common path off-axis interferometers, this PDI has a simple optical setup, easy optical implementation and outstanding measurement ability with high precision, measurement efficiency and stability. Several experimental results will be provided to demonstrate the effectiveness of the proposed system.

Coupling Michelson-like lateral shear interferometric microscopy with self-referencing numerical phase calibration for quantitative measurement of 3D surface morphology of biological cells

A Michelson interferometer is commonly used for evaluating the morphology of a cell. However, the interference imaging with reference and object beams is easily affected by external vibrations and environmental disturbances, leading to unstable interference patterns. In this paper, the three-dimensional surface morphology of the biological cell is evaluated by a new quantitative phase imaging method, which couples Michelson-like lateral shear interferometric microscopy with self-referencing numerical phase calibration. The Michelson-like lateral shear interferometric microscopy is constructed by replacing the two plane mirrors of the traditional Michelson interferometer with two common right-angle prisms and generates interference fringe patterns. The lateral shear is created and freely adjustable by simply translating/or rotating one right-angle prism. To calculate the phase information of the biological cells quantitatively, the classical Fourier transform method is used to process the recorded interferogram, and then the self-referencing numerical phase calibration method is utilized for acquiring accurate phase information. Successfully achieving quantitative phase imaging of a cell verifies the feasibility and practicability of the proposed method.

Dual-shot approach for polarization retrieval through a scattering medium

A dual-shot technique based on the field basis addition of two statistically independent speckle patterns is developed to recover an input polarization through a scattering layer. It is proposed theoretically, and demonstrated both numerically and experimentally that by tuning the linear polarization orientation of the reference speckle pattern to 0° and 45° w.r.t. the x-axis, polarization retrieval of an object beam through a scattering layer can be achieved by measuring the degree of polarization of the superposed speckle pattern. The proposed technique can have a wide range of applications in polarization sensing and biomedical imaging.

Structure probing by holographic imaging at nanometer scale with X-ray lasers (SPHINX)

The SPHINX project aims generating femtosecond-exposure X-ray holograms of microscopic samples and of their internal parts with nanometer resolution. The application is based on a new implementation of the phase-contrast holography that overcomes the main limitations encountered in the current systems (most based on absorption-contrast), namely the low energy range, the limited detector granularity and the weak illumination. The combination of polycapillary lenses, large X-Ray CCD arrays with small pixel size and XFEL sources allows splitting the beam, focusing, magnification and phase-contrast imaging in the keV energy range. Due to the wavelength-dependent optical behavior of the samples, the refractive diffraction reduces the diffraction limit together with a fast drop of the characteristic angles, both essential for the resolving power (given the limited X-ray detector pitch), while also eliminating the shadow effect and giving access to full structure probing. The key parameters are defined by the focusing optics, which could be, according to the beam and sample sizes, a polycapillary micro semi-lens or a combination of the former with a parabolic monocapillary. The advantage of “non-perfect” optics (not providing a point-like focus) is their divergence, driven mostly by the single waveguide. This allows sending on the same detector area the diverging object and reference beams (Fresnel configuration), both provided by a single optical element, condition unreachable with a Fresnel lens or a crystal mirror. Moreover, the femtosecond exposure time on X-FELs permits holographic reconstruction of in-vivo cell elements, viruses and nanorobotic devices during ultrafast molecular processes, yet unexplored by imaging techniques.

Defect Isolation from Whole to Local Field Separation in Complex Interferometry Fringe Patterns through Development of Weighted Least-Squares Algorithm

In this paper, based on Gaussian 1σ-criterion and histogram segmentation, a weighted least-squares algorithm is applied and validated on digital holographic speckle pattern interferometric data to perform phase separation on the complex interference fields. The direct structural diagnosis tool is used to investigate defects and their impact on a complex antique wall painting of Giotto. The interferometry data is acquired with a portable off-axis interferometer set-up with a phase-shifted reference beam coupled with the object beam in front of the digital photosensitive medium. A digital holographic speckle pattern interferometry (DHSPI) system is used to register digital recordings of interferogram sequences over time. The surface is monitored for as long as it deforms prior to returning to its initial reference equilibrium state prior to excitation. The attempt to separate the whole vs. local defect complex amplitudes from the interferometric data is presented. The main aim is to achieve isolation and visualization of each defect’s impact amplitude in order to obtain detailed documentation of each defect and its structural impact on the surface for structural diagnosis purposes.

Dynamic quantitative phase imaging using calcite crystal-based temporally stable interferometer

This paper describes the development of a common path off-axis quantitative phase microscope (QPM), enabling high-speed quantitative measurements of sub-cellular dynamics in a live cell. The proposed 4f optical system consists of a polarizer, lenses, calcite crystal, pinhole and analyser, attached to the output port of an optical microscope converting it into a temporally stable QPM. The temporal phase stability of this optical configuration is measured to be equal to ∼20 mrad without a vibration isolation table. The utility of the microscope is demonstrated by conducting experiments on a polystyrene sphere (dia. 12 μm) and human red blood cells (RBCs). Furthermore, the developed system is implemented to study temporal membrane fluctuation in human RBCs over ∼30s and mouse embryonic fibroblast cell dynamics over 2 hours. Therefore, the system offers an energy-efficient and simple solution for generating object and reference beams for common-path QPM, making it an attractive alternative to existing approaches.

Improving resolution in two orthogonal orientations from a single-shot digital holographic microscopy

We demonstrate a single-shot digital holographic microscopy technique to improve the diffraction-limited resolution in two orthogonal orientations simultaneously by dual-channel orthogonal polarization multiplexing approach. Orthogonally polarized two oblique beams are employed to illuminate the sample and two reference beams with mutually orthogonal polarization are interfered with the object beams in a custom-designed Mach–Zehnder configuration. This technique is potentially beneficial to encode high frequency sample information from two orthogonal directions simultaneously in a single recorded hologram where the high frequency spectra is synthesized by the selective spectral stitching. Thus, the resolution is enhanced along two orientations from a single-shot hologram in this work. Both the simulation and experimental results are shown for the proposed technique with around 2-fold resolution enhancement over the diffraction limit.

Double field-of-view single-shot common-path off-axis reflective digital holographic microscope

Digital holography is a versatile three-dimensional imaging technique that has the ability to record the complex wave-front of an imaged object in two-dimensions and retrieve it in three-dimensions. Several technical challenges of digital holographic systems have been overcome by proposing single-shot acquisition and common-path configurations. However, the limited fiel-of-view (FOV) of digital holography is the most fundamental and technically challenging aspect of this technology. With this in mind, we have developed a digital holographic microscope (DHM) with a doubled FOV together with it leverages single-shot acquisition, common-path, and off-axis configuration and operates in the reflection mode. The double FOV is achieved by spatial frequency multiplexing of two different areas of the object beam by the use of a cube beam splitter. The common-path and off-axis configuration are obtained by employing a plate beam splitter just before the microscope objective. Several experiments are carried out, and the results are presented to demonstrate the validity and effectiveness of the proposed DHM for quantitative phase imaging of (semi) transparent and reflective objects. Based on the experimental results, the proposed microscope shows advanced performance in biomedical imaging as well as inspection of engineered surfaces with its simplicity, higher stability (temporal and mechanical), compactness, low cost, and most importantly double FOV capabilities.

Multiple image encryption based on multiplexing holography with Kramers–Kronig relations

Multiplexing techniques can store multiple wavefront information of object beams in one hologram, which is a way to realize multi-image encryption. In this paper, an optical multi-image encryption method based on Kramers-Kronig multiplexing digital holography is proposed. In the encryption process, multiple images are subjected to Fresnel diffraction at a certain distance and modulated by a random phase mask. The modulated images then interfere with the reference beam and form a noise-like compound ciphertext. In the decryption process, the information of the original images can be extracted directly from the positive frequency part of the spectrum. Compared to the traditional image encryption based on off-axis digital holography, this method enables the decryption of images in the case of spectrum overlap. The feasibility of our proposed method is demonstrated through numerical simulations, which provide a novel approach for the field of multi-image encryption based on digital holography.

A differential phase spectropolarimeter for measuring optical rotatory dispersion

This paper considers the features of polarimetric methods used for the analysis of optically active substances. It presents a design of a differential spectropolarimeter operating by analyzing the phase difference between two harmonical signals received when splitting a laser beam from a common source into separate reference and object beams. The expediency of using the Fourier transform to calculate the phase difference of differential spectropolarimeter signals is noted. The results of calculating the parameters of the measuring method and the results of an experimental study of reference polarimetric plates at various wavelengths are presented. The error in measuring the optical rotation angle in the wavelength range 405–780 nm did not exceed ±0.005°.

Slightly Off-Axis Digital Holography Using a Transmission Grating and GPU-Accelerated Parallel Phase Reconstruction

Slightly off-axis digital holography is proposed using transmission grating to obtain quantitative phase distribution. The experimental device is based on an improved 4f optical system in which a two-window input plane is used to form the object beam and reference beam. Then, the two beams are diffracted into multiple orders by the transmission grating placed at the Fourier plane. By applying a modified Michelson configuration, the interference patterns can be generated by the object and reference beams from different diffraction orders. After translating the grating, a random phase shift can be introduced to the hologram. To demonstrate the feasibility of our method, both thick and thin phase specimens are retrieved using two carrier phase-shifting holograms. Furthermore, we use the phase reconstruction algorithm based on the NVIDIA CUDA programming model to reduce the retrieval time. Meanwhile, we optimize the discrete cosine transform (DCT)-based least-squares unwrapping algorithm to unwrap the phase. By porting the entire phase reconstruction process to the graphics processing unit (GPU), the phase retrieval acceleration and execution efficiency significantly improve. To demonstrate the feasibility of our method, it is found that our method can measure the surface profiles of standard elements, such as a plano-convex cylinder lens and a microlens array, with a relative error of about 0.5%. For holograms with a different phase shift, the root-mean-square (RMS) value of the phase difference for the main imaging region is about 0.2 rad. By accelerating the phase reconstruction with GPU implementation, a speedup ratio of about 20× for the thick phase specimen and a speedup ratio of about 15× for the thin-phase specimen can be obtained for holograms with a pixel size of 1024 × 1024.

Predictors of Outcomes in 900 Alveolar Bone Grafts.

Significant discrepancies exist in the reported variables influencing alveolar bone graft outcomes. The purpose of this study was to evaluate graft success and identify outcome predictors in a large patient cohort using an objective cone beam computed tomography assessment tool. Consecutive patients with cleft lip/palate who underwent alveolar bone grafting by 1 surgeon were included. Predictor variables were age at graft, oronasal fistula, canine position, concurrent premaxillary osteotomy, size of cleft, presence of bony palatal bridge, history of failed graft, location of primary repair, and surgeon experience. The outcome variable was graft success, determined using a cone beam computed tomography assessment tool and defined as a score of 3 or 4 (out of 4) in the following domains: vertical bone level, labiopalatal thickness, and nasal piriform symmetry. The sample included 900 alveolar cleft sites (median graft age, 9.9 years). The success rate was 94.6%. Presence of an erupted canine, large cleft defect, or premaxillary osteotomy were independent predictors of graft failure; presence of a bony palatal bridge was associated with graft success ( P < 0.05). Presence of an erupted canine, large bony defect, or premaxillary osteotomy increase the risk of failure, and a bony palatal bridge portends success. Age 12 years or older, visible oronasal fistula, history of failed graft, primary cleft repaired at outside institution, and surgeon experience were associated with higher graft failure, but were not independent predictors when controlling for covariates. Surgeons should be aware that these factors in combination increase the odds of graft failure. Risk, III.

A compact digital holographic system based on a multifunctional holographic optical element with improved resolution and field of view

The spatial resolution and field of view (FOV) of the digital holographic system are limited by the finite pixel size of the image sensor. In order to record high-resolution digital holograms of larger objects at a shorter object-to-sensor distance, which is desirable for applications such as display, non-destructive testing, etc., the holographic system must have a larger FOV. We propose a compact off-axis digital holographic setup in which a multifunctional holographic optical element (MHOE) is employed in the path of the object and reference beams to improve the system's resolution simultaneously enhancing the FOV by utilizing the same specifications of the digital sensor. In this configuration, a diffractive optics property of the MHOE enhances the spatial resolution of the optical system. At the same time, the lens function recorded in the same MHOE enables a large imaging area. The experimental results obtained with the proposed configuration are compared to conventional digital holography, where the proposed configuration shows a 423% increase in the FOV. The quality of the reconstructed image with the proposed configuration is measured by calculating the structural similarity index measure (SSIM) value. Experimental results and simulations have verified the feasibility of the proposed system. Furthermore, the proposed system is incredibly compact due to the use of the MHOE.

Digital holographic nanoscopy for erythrocyte, nanoparticle and quantum dot characterization

Optical detection of biological cells and nanoparticles is a challenging task in optical physics due to the individual nanoparticles' low inherent scattering, size, and shape. High magnification is required for the study of such particles. In the present work, we have introduced a modified Digital Holographic Microscopy (DHM) for qualitative and quantitative optical characterization of biological cells, nanoparticles and quantum dots through phase measurement. The proposed system can measure a quantum dot of a minimum size of 6.8 nanometers with 1,53,284X magnification by placing two Microscope Objective (MO) lenses in the path of the object beam of the DHM. We have recorded digital holograms of the specimen for different combinations of MOs by varying distances between them. The system can characterize the specimen of micro to nanometer scales by varying its magnification as per requirements. The results are shown for human erythrocytes of diameter of 7.31 ± 0.08 µm & thickness of 2.3 ± 0.058 µm and gold nanoparticles (AuNPs) of different sizes (6.8 nm - 50 nm). The size of erythrocytes and AuNPs are determined experimentally using the DHM by mapping with USAF-1951 high-resolution microscope targets. The obtained results are verified by Field Emission Scanning Electron Microscopy (FESEM) and High-Resolution Transmission Electron Microscopy (HRTEM) measurements.

Three‐dimensional phase measurement of transparent gas by high‐speed digital holographic tomography system

A high-speed digital holographic tomography system based on off-axis multiplexed recording is proposed for fast three-dimensional (3-D) phase measurements of transparent gasses. Object beams pass through the object at 0, 45, 90, and 135° and interfere with the reference beam to form a hologram that is recorded by a single camera. The phase information of each optical path is reconstructed by the Fresnel diffraction integral calculation, and then the 3-D phase information of the object can be obtained by the simple back-projection algorithm. The recording speed of the system depends entirely on the frame rate of the camera. In the experiments, we successfully measured the 3-D phase information of an asymmetric gas flow with the proposed system at 65 frames per second.

Pareto frontier for steel-reinforced concrete beam developed based on ANN-based Hong-Lagrange algorithm

ABSTRACT Multi-objective optimization (MOO) is always a challenging issue for engineers in the field of structural engineering, where several objective functions must be satisfied under equality and inequality constraints to meet requirements imposed by engineers and decision-makers. This study proposes a novel approach to solve MOO problems for steel-reinforced concrete (SRC) beams using an artificial neural network (ANN)-based Hong-Lagrange algorithm. Proposed method in this paper optimizes three specific objective functions, including cost (CIb), CO2 emissions, and beam weight (W), simultaneously. Neural networks are trained by 200,000 samples, which are randomly generated by structural mechanics-based calculations, to derive three specific objective functions. Unified objective function is, then, proposed based on weight fractions of each objective function. An ANN-based Hong-Lagrange technique identifies optimal design parameters within the bounds constrained by 16 inequalities against external loads. The proposed method yields a set of optimal results, creating a Pareto frontier that optimizes multiple objectives. Pareto frontier using an ANN-based Hong-Lagrange algorithm is well compared with the lower boundary of large datasets of random designs which include 133,711 samples obtained by structural mechanics. A cost of an SRC beam is obtained as 219,279.1 KRW/m by an ANN-based Hong-Lagrange algorithm with an error of −0.14% verified by structural mechanics.