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• An automatic focusing method based on connected domain analysis (CDA) was proposed to generate the focusing evaluation curve. • The CDA method can focus multi-focus holograms without region of interest segmentation. • The CDA method was successfully applied to multi-focus focusing in five types of plankton samples and actual seawater samples. • The CDA method was able to provide focusing guidance over a wide range of z-axis distances. Holography is widely used for imaging plankton because of its large depth of field. Autofocusing is a critical step in holographic imaging, where the optimal focal plane is determined by locating the extremum of the evaluation function curve. However, most of these methods perform auto-focusing on single focus holograms. To apply these methods to multi-focus holograms, the hologram must be subjected to object segmentation. It is difficult to achieve good results when focusing on holograms with small objects and large depth of field. Therefore, we propose a multi-focus autofocus method based on connected domain analysis (CDA), which allows focusing on multiple objects at different focal lengths simultaneously without image segmentation. Each object generates a focus evaluation curve, resulting in high focusing accuracy. We set up an in-line holographic optical system with a 30 mm depth of field and recorded holograms of Nauplius, Cladocera, Rotifera, Copepods, Noctiluca scintillans and real seawater samples. We demonstrated the robustness of the CDA algorithm for different target types and its effectiveness in focusing multi-focus images by applying it to holograms of six types of samples. [ABSTRACT FROM AUTHOR]

For non-contact deformation testing, digital holographic interferometry is a prominent optical technique where the first and second order interference phase derivatives directly embed information about the strain and curvature distributions of a deformed object. Hence, reliable extraction of multiple order phase derivatives is of great practical significance; however, this problem is marred by several challenges such as the need of multiple differentiation operations, complex shearing operations and performance degradation due to noise. In this paper, we introduce a deep learning approach for the direct and simultaneous estimation of first and second order phase derivatives in digital holographic interferometry. Our method's performance is demonstrated via rigorous numerical simulations exhibiting wide range of additive white Gaussian noise and speckle noise. Moreover, we substantiate the practical efficacy of our proposed method for processing deformation fringes acquired via digital holographic interferometry. • Deep learning approach for simultaneous estimation of multiple order phase derivatives in digital holographic interferometry. • Strong tolerance against severe noise. • Eliminates requirement of numerical differentiation, filtering, and shearing operations. • Practical validation of the method for non-destructive deformation metrology. [ABSTRACT FROM AUTHOR]

• In the measurement of millimeter-wave broadband systems, cumbersome data processing and complex system design have always been the pain points and difficulties of measurement. • Therefore, this paper proposes a single-frequency millimeter-wave autofocus imaging algorithm to realize autofocus measurement of millimeter-wave narrowband holographic imaging. • The experimental results prove that our method is effective. Compared to broadband systems, single-frequency millimeter-wave (SFQ-MMW) imaging systems can significantly simplify system complexity, but can only obtain two-dimensional information of the target. Moreover, the position of the reference plane must be adjusted in real time during the imaging process to obtain a high-quality focusing effects. Therefore, this paper proposes a SFQ-MMW three-dimensional imaging algorithm. In the plane wave spectrum domain, the propagation operator is used as a focusing term to accurately locate the target focus. Only single-frequency echo data is required to retrieve information and reconstruct high-quality images. This method can significantly improve the efficiency of near-field millimeter wave measurement and imaging. This work facilitates applications in rapid target identification and characterization. The performance of this method was tested through numerical simulation. Finally, validation was performed on real data in an independently developed system. The results show that the test results are in line with expectations, and the imaging efficiency has been significantly improved. [ABSTRACT FROM AUTHOR]

In this work, an adaptive holographic interferometer was implemented for the measurement of a micromechanical oscillator frequency. A silicon micro-cantilever mounted on a piezoquartz plate was used as the sensing element. Out-of-plane vibrations of the cantilever were excited using a sinusoidal electrical signal. The cantilever vibrations were measured with the adaptive interferometer using two waves coupling in a semi-insulating photorefractive CdTe:V crystal. In the experiment, the mass of absorbed molecules of bovine serum albumin (BSA) was measured at various concentrations of water solution. The biosensor demonstrated the ability to measure the concentration of BSA in water solutions with a concentration of 0.2 mg/mL. The result shows the possibility of using adaptive interferometry to detect the vibration of micromechanical sensors and the potential prospects for building biosensors based on them.

• Most simple, stable, robust lateral shearing interferometer using a polarization grating compared to other interferometers. • Based on the balanced achromatic scheme between two shearing wavefronts, any kinds of optical source, even broadband light sources such as white light can be available. • Thoroughly new concept to estimate the surface roughness. • Snapshot roughness capability opposed to other optical techniques and valuable measurement results. A compact optical roughness measurement sensor based on lateral shearing interferometry is theoretically described and experimentally verified. By adopting the advanced surface roughness parameter extraction methods based on statistical machine learning technique and the partial integration approach, the sensor using a polarization grating and a polarization camera can instantaneously obtain a surface gradient map and provide reliable surface roughness parameters. To verify the operation and the performance of the sensor, a flat mirror and roughness standard specimens were measured, and the results were compared with those of a white light scanning interferometer as the reference values. As a result, the roughness parameters were very close to the reference values with <5 nm accuracy and <0.1 nm repeatability. [ABSTRACT FROM AUTHOR]

Quantifying the droplet field near the atomizer exit poses a challenge due to its three-dimensional (3D), multiscale and turbulent characteristics. An optical measurement method named dual-camera high-resolution holographic particle tracking velocimetry (DCHR-HPTV) is proposed. This method enables the extraction of near-field spatial Sauter mean diameter (SMD) distribution and three-dimensional two-component (3D-2C) velocity field, from off-axis hologram pairs with a frame interval of 6 μs, recorded using two synchronized industrial cameras and pulsed lasers. The system achieves a resolution of 9344 × 7000 pixels with an individual pixel size (d p i x) of 3.2 μm. The droplet size measurement range is from 10 μm to above 500 μm with an absolute error within 3 μm. The velocity measurement range is adjustable and is set to be 0 to 38.4 m/s in this study, with errors of 0.23 m/s and 0.15 m/s for horizontal and axial components, respectively. The method is applied to investigate a spray region of 29 mm × 20 mm with a depth of 35 mm (equivalent to 20.3 cm3) at the exit of an air-blast atomizer. The spatial distribution of circumferentially integrated SMD along radial and axial directions is obtained. Statistical analysis is performed on both spatial and quantity distributions of droplet 3D-2C velocities. Concurrently acquired droplet size and velocity in the central toroidal recirculation zone (CTRZ) indicate that both the increasing air pressure and enlarged size range lead to a weakened droplet backflow motion. This method, distinguished by its large field of view and high resolution for particle velocimetry, is suited for dynamic analysis of near-nozzle droplet fields and can be employed in various testing scenarios involving 3D motion of micron-sized particles within multiscale flow fields. • A 65-million-pixel dual-camera high-resolution holographic PTV method is proposed. • Transient 3D-2C droplet velocity field including CTRZ is quantitatively visualized. • Spatial and quantity distributions of droplet velocities is analyzed statistically. [ABSTRACT FROM AUTHOR]

• A novel manufacturing approach for positive planar refractive microlens was proposed. • High-index chalcogenide polymer was infilled into concave microlens-featured glass substrate to create effective positive microlens. • Phase modulation of such embedded element was mapped with digital holographic interferometry. • The fabricated sample demonstrated its suitability for Hartmann wavefront measurements. Planar microlens components are highly desired in micro-systems for their compactness and ability to integrate with other planar elements. In this paper, we propose an alternative facile approach to producing positive planar microlens components by infilling concave microlens featured glass encapsulation with high refractive index chalcogenide polymer. The presented refractive microlens components have several advantages: cost-efficient to process, high transmission in broadband spectrum, the ability to generate real focus and real image, and being well-protected by its planar glass encapsulation. Both single and arrayed samples were fabricated to demonstrate the effectiveness of the manufacturing process. The optical properties of the fabricated samples, including phase modulation, imaging performance, and spectrally operational region, were thoroughly characterized. Wavefront calibration with the prepared sample revealed its potential application in practical engineering fields. [ABSTRACT FROM AUTHOR]

Spiral interferometry is a technique that accurately measures changes in 3D structures or refractive indices by converting phase changes into spiral fringe patterns. The spiral fringe patterns consist of phase distributions, which are wrapped from 0 to 2 π , requiring phase unwrapping techniques. Phase unwrapping transforms a discontinuous phase image from 0 to 2 π into a continuous phase image, which can ultimately be reconstructed into 3D information. The 3D reconstructed information is affected by the unwrapped phase information with noise. Among the phase unwrapping methods, the number-theoretical phase unwrapping method used in 1D structured light is a unique approach that unwraps the phase into a step function. Due to its insensitivity to noise, this method is an effective solution for improving phase unwrapping in noisy environments. However, due to the same characteristics, the resolution inevitably decreases. In this paper, we propose a super-resolution based numerical unwrapping method applicable to two-dimensional spiral patterns. Based on multi-wavelength interpolation, this method not only retains the advantage of the number-theoretical phase unwrapping method, which is insensitive to noise, but also compensates for its disadvantage of resolution degradation. The proposed method uses the basic concept of generating sub-step information by multi-wavelength interpolation and performing super-resolution based on this concept. We perform simulations and experiments to verify the validity. As a result of the verification, it is confirmed that the super-resolution effect of the number-theoretical unwrapping in the 2D spiral fringe patterns can be achieved by the proposed method. [ABSTRACT FROM AUTHOR]

Calorimetric dosimetry through digital holographic interferometry (DHI) is a homogeneous dosimetry method for measuring the absolute absorbed dose in non-opaque phantoms. Different methods have already been proposed for measuring the distribution of dose using this homogeneous calorimetric dosimetry technique. In this research work, a new, simple, and easy-to-use method for determining the total absorbed dose via DHI is proposed. The method is based on fringe detection, counting, and using our derived calibration equations to obtain the total absorbed dose values. To prove the capability of the method in accurate estimating of the absolute total absorbed dose, the dosimetry process in this technique is computationally modeled. It is shown that the mean relative error for the obtained total absorbed dose from high-energy electrons in PMMA phantom amounts to 4.8% by the proposed method. [ABSTRACT FROM AUTHOR]

The proposed multitask bidirectional digital coding metasurface has powerful ability in manipulation of both reflection and transmission EM waves, which is incapable for previously reported metasurfaces and may provide a simple way to extend the functionality and information capacity of high-efficiency metadevices. Keywords: bidirectional; digital coding metasurface; full space; multi-band; multi-task EN bidirectional digital coding metasurface full space multi-band multi-task 2977 2987 11 05/26/22 20220615 NES 220615 1 Introduction Metasurface, as a two-dimensional (2D) planar version of metamaterial, provides an easy way to control the electromagnetic (EM) waves by properly engineering and arranging periodic or aperiodic subwavelength artificial meta-atoms [[1]], [[2]], [[3]], which can not only inherit the superior capabilities of metamaterials in manipulating the EM properties, such as phase [[4]], [[5]], [[6]], [[7]], magnitude [[7]], [[8]], [[9]], polarization [[10]], but also overcome the challenges encountered in metamaterials, such as high losses, bulk, difficult manufacturing, and so on. Here, we propose a multitask bidirectional digital coding metasurface that can achieve independent controls of both reflection and transmission waves in different frequency bands, and perform different functions when the EM waves are incident from the front and the back of the metasurface, respectively. [Extracted from the article]

Ultra‐low wavenumber or ultra‐low frequency (ULF) Raman spectroscopy using holographic optics is an emerging technique to obtain spectral signatures of chemicals in low energy corresponding to their phases, crystallinity, isomerism, and environmental conditions such as temperature. Commercial turn‐key systems employ mechanical turrets and other such optomechanical moving elements to accommodate multiple laser excitations, which are incident normally on the sample, and the Raman signal is collected in a 180° backscattering configuration. Here, we have developed a system consisting of two single‐longitudinal mode (SLM) lasers and a single‐stage spectrometer. Selected notch filters were based on the volume holographic grating technology providing output beam at a certain angle, which facilitates the possibility of different angles of incidence of the excitation laser on the sample. This adaptive ULF Raman system, therefore, is not only able to acquire high‐quality low‐wavenumber spectral fingerprints of various chemicals but can also be easily reconfigured for differential spectral studies. [ABSTRACT FROM AUTHOR]

Digital holography is well adapted to measure any modifications related to any objects. The method refers to digital holographic interferometry where the phase change between two states of the object is of interest. However, the phase images are corrupted by the speckle decorrelation noise. In this paper, we address the question of de-noising in holographic interferometry when phase data are polluted with speckle noise. We present a new database of phase fringe images for the evaluation of de-noising algorithms in digital holography. In this database, the simulated phase maps present characteristics such as the size of the speckle grains and the noise level of the fringes, which can be controlled by the generation process. Deep neural network architectures are trained with sets of phase maps having differentiated parameters according to the features. The performances of the new models are evaluated with a set of test fringe patterns whose characteristics are representative of severe conditions in terms of input SNR and speckle grain size. For this, four metrics are considered, which are the PSNR, the phase error, the perceived quality index and the peak-to-valley ratio. Results demonstrate that the models trained with phase maps with a diversity of noise characteristics lead to improving their efficiency, their robustness and their generality on phase maps with severe noise. [ABSTRACT FROM AUTHOR]

We present an array-based volume holographic optical element (vHOE) recorded as an optical combiner for novel display applications such as smart glasses. The vHOE performs multiple, complex optical functions in the form of large off-axis to on-axis wave front transformations and an extended eye box implemented in the form of two distinct vertex points with red and green chromatic functions. The holographic combiner is fabricated by our extended immersion-based wave front printing setup, which provides extensive prototyping capabilities due to independent wave front modulation and large possible off-axis recording angles, enabling vHOEs in reflection with a wide range of different recording configurations. The presented vHOE is build up as an array of sub-holograms, where each element is recorded with individual optical functions. We introduce a design and fabrication method to combine two angular and two spectral functions in the volume grating of individual sub-holograms, demonstrating complex holographic elements with four multiplexed optical functions comprised in a single layer of photopolymer film. The introduced design and fabrication process allows the precise tuning of the vHOE's diffractive properties to achieve well-balanced diffraction efficiencies and angular distributions between individual multiplexed functions. [ABSTRACT FROM AUTHOR]

Photoinduced gyrotropy (nonlinear optical activity) of polarization-sensitive luminescent recording materials based on various drinking and mineral waters are herein studied by polarization-luminescent holography methods. Photoluminescence spectra and spectra of the degree of circularity of (circular) polarization luminescence of a reconstructed phantom object are obtained. A significant modification of the dynamic multiplex luminescent Denisyuk holograms is observed in the medium during the transition from the racemic to chirally pure phases. In particular, a polarization-holographic memory of the gyrotropic properties is expressed in the considered aqueous media. Polarization-holographic analysis of the optical polarization spectra of the aqueous media makes it possible to obtain additional information about anisotropic-gyrotropic holographic materials, namely, the intrinsic chirality of the components of each compound present in the medium. [ABSTRACT FROM AUTHOR]

In the present work, we consider the recently proposed non-interacting Barrow holographic dark energy (Int. J. Geom. Methods Mod. Phys.18(01) (2021) 2150014, doi:10.1142/S0219887821500146) with Hubble horizon as IR cutoff in a flat FLRW universe. We examine the evolutionary behavior of deceleration parameter and equation of state parameter for the different Barrow exponent Δ , and observe suitable behavior in the model. We choose Δ > 2 in the non-interacting Barrow holographic dark energy which is explained by a phantom scalar field, then we exhibit the phantomic narration of the Barrow holographic dark energy with Δ > 2 and reconstruct the potential of the phantom scalar field. [ABSTRACT FROM AUTHOR]

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Holographic display is considered as the most promising three-dimensional (3D) display due to its unique feature of reconstructing arbitrary wavefronts. However, the limited étendue, which hinders the immersive experience of observers, remains a major unresolved issue in holographic display technique. In this paper, we propose a novel approach to tweak the constraints of étendue by expanding the energy envelope in holographic display via mutually coherent multi-illumination. The proposed concept contains both a light source design for generating a mutually coherent multi-directional wave and a computer-generated hologram optimization framework for providing high-resolution 3D holograms. To verify the proposed approach, a benchtop prototype of a holographic near-eye display providing an intrinsic large exit-pupil is implemented. The experimental results clearly show that the exit-pupil is effectively expanded by four times and an appropriate viewpoint image is reconstructed according to the view position. [ABSTRACT FROM AUTHOR]

In the present work, we propose a compact digital holographic camera (DHC) with extended stochastic illumination for full-field non-destructive inspection of silicon optics fabricated in a computerized numerical control machine. The developed technique overcomes the limitation of digital holography imparted by the finite size of the active area of the recording sensor that can image a specular surface. The original aspect of this research work is to develop a system that enables reconstruction and testing of a specular surface. For this a dual diffuser configuration is incorporated in a compact DHC developed for non-destructive testing (NDT) applications. The generation of a stochastic illumination beam using the diffusers is explained by simulating the propagation of a light beam through a random phase function of the scattering medium. The stochastic optical field produced by the combination of diffusers in the DHC makes the camera suitable for NDT of the specular surface of silicon optics. The effects of the number of diffusers and their relative positions on the imaging area of the specular object are studied for development of an optimized configuration of DHC. Applicability of the proposed scheme is demonstrated through detection of defects in silicon optics using digital holographic interferometry. [ABSTRACT FROM AUTHOR]

I review holographic models for (dense and cold) nuclear matter, neutron stars, and their mergers. I start by a brief general discussion on current knowledge of cold QCD matter and neutron stars, and go on discussing various approaches to model cold nuclear and quark matter by using gauge/gravity duality, pointing out their strengths and weaknesses. Then I focus on recent results for a complex bottom-up holographic framework (V-QCD), which also takes input from lattice QCD results, effective field theory, and perturbative QCD. Dense nuclear matter is modeled in V-QCD through a homogeneous non-Abelian bulk gauge field. Feasible "hybrid" equations of state for cold nuclear (and quark) matter can be constructed by using traditional methods (e.g., effective field theory) at low densities and the holographic V-QCD model at higher densities. I discuss the constraints from this approach to the properties of the nuclear to quark matter transition as well as to properties of neutron stars. Using such hybrid equations of state as an input for numerical simulations of neutron star mergers, I also derive predictions for the spectrum of produced gravitational waves. [ABSTRACT FROM AUTHOR]

Hydrogen is a promising alternative to carbon based energy carriers and may be stored in large quantities in subsurface storage deposits. This work assesses the impact of static (density and phase equilibria) and dynamic (viscosity and diffusion coefficients) properties on the pressure field during the injection and extraction of hydrogen in the porous subsurface. In a first step, we derive transport properties for water, hydrogen and their mixture using the Perturbed‐Chain Statistical Associating Fluid Theory equation of state in combination with an entropy scaling approach and compare model predictions to alternative models from the literature. Our model compares excellently to experimental transport coefficients and models from literature with a higher number of adjustable parameters, such as GERG2008, and shows a clear improvement over empirical correlations for transport coefficients of hydrogen. In a second step, we determine the effect of further model reduction by comparing our against a much simpler model applying empirical transport coefficients from the literature. For this purpose, hydrogen is periodically injected into and extracted out of a dome‐shaped porous aquifer under a caprock. Our results show that density and viscosity of hydrogen have the highest impact on the pressure field, and that a thermodynamic model like the new model presented here is essential for modeling the storage aquifer, while keeping the number of coefficients at a minimum. In diffusion‐dominated settings such as the diffusion of hydrogen through the caprock, our developed diffusion coefficients show a much improved dependence on temperature and pressure, leading to a more accurate approximation of the diffusive fluxes. Key Points: We model the phase behavior of pure hydrogen and the binary hydrogen‐water mixture using the Perturbed‐Chain Statistical Associating Fluid Theory equation of stateNew entropy scaling relations for the transport properties of hydrogen and water and diffusion coefficients of their mixture are derivedThe impact of the newly derived fluid properties is analyzed for a scenario of hydrogen storage in a porous aquifer [ABSTRACT FROM AUTHOR]

As a general rule, the development of specific processing algorithms requires to accurately simulate data of interest by generating it as close as possible to the reality. In digital holographic interferometry and related approaches, the experimental phase data that are used for metrology purposes are corrupted by the speckle decorrelation noise. Thus, they require to be processed with advanced algorithms. To check the performances of de-noising algorithms before applying to real experimental data, simulations have to be carried out to provide quantitative errors and other related metrics of those performances. In litterature, many published papers dealing with the problem of phase de-noising in digital holographic interferometry consider Gaussian statistics and the hypothesis of noise stationarity, for simulating test data. However, considering the point spread function of digital holographic imaging systems, the noise in the phase data does not follow the Gaussian statistics. This means that considering Gaussian noise in data simulations is to make a big mistake on the nature of the noise in the holographic system. Therefore, in this paper, one aims at demonstrating that the Gaussian statistics are not well appropriated for simulating noise in holography, because such an approach systematically overestimates the performances of the algorithms. Then, using appropriate metrics such as mean standard deviation error, quality index, and peak-signal-to-noise-ratio, the paper demonstrates that the realistic speckle noise must be taken into account and correctly simulated for benchmarking overall algorithm performances. [ABSTRACT FROM AUTHOR]

Single-beam multiple-intensity iterative phase retrieval is a high-precision and lens-free computational imaging method, which reconstructs the complex-valued distribution of the object from a volume of axially captured diffraction intensities using the post-processing algorithm. However, for the object with slowly-varying waves, the method may encounter the problem of convergence stagnation since the lack of diversity between the captured intensity patterns. In this paper, a novel technique to enhance phase retrieval using holographic illumination is proposed. One special computer-generated hologram is designed, which can generate multiple significantly different images at the required distances. The incident plane wave is firstly modulated by the hologram, and then the exit wave is used to illuminate the object. Benefitting from this holographic illumination, remarkable intensity changes in the given detector planes can be produced, which is conducive to fast and high-accuracy reconstruction. Simulation and optical experiments are performed to verify the feasibility of the proposed method. [ABSTRACT FROM AUTHOR]

In the paper is described possibility of holographic interferometry in research of heat transfer above samples. Experiments with utilization of this method enable to explain many of actions going in environment and in phase interface between material and this environment in transport of heat. The presented experiments are aimed at verifying the possibilities of safe thermal loading of wood using with metal protective plate. [ABSTRACT FROM AUTHOR]

Given that spin and orbital angular momenta of photons have been widely investigated in optical communication and information processing systems, efficient decoding of optical vortex states using a single element is highly anticipated. In this work, a wavelength-independent holographic scheme has been proposed for total angular momentum sorting of both scalar and vector vortex states with a stationary broadband geometric-phase waveplate by means of reference-free shearing interferometry. The entangled spin and orbital angular momentum modes can be distinguished simultaneously based on the spin–orbit optical Hall effect in order to realize single-shot vortex detection. The viability of our scheme has also been demonstrated experimentally. [ABSTRACT FROM AUTHOR]

Holograms can shape wavefronts to produce arbitrary acoustic images. In this work, we experimentally demonstrate how acoustic holograms can produce controlled thermal patterns in absorbing media at ultrasonic frequencies. Magnetic resonance imaging (MRI)-compatible holographic ultrasound lenses were designed by time-reversal methods and manufactured using 3D-printing. Several thermal holographic patterns were measured using MRI thermometry and a thermographic camera in gelatin-milk phantoms and in an ex vivo liver tissue. The results show that acoustic holograms enable spatially controlled heating in arbitrary regions. Increasing the temperature using low-cost and MRI-compatible holographic transducers might be of great interest for many biomedical applications, such as ultrasound hyperthermia, where the control of specific thermal patterns is needed. [ABSTRACT FROM AUTHOR]

Typically, an interactive system evolves towards thermal equilibrium, with hydrodynamics representing a universal framework for its late-time dynamics. Classification of the dynamical fixed points (DFPs) of a driven Quantum Field Theory (with time dependent coupling constants, masses, external background fields, etc.) is unknown. We use holographic framework to analyze such fixed points in one example of strongly coupled gauge theory, driven by homogeneous and isotropic expansion of the background metric — equivalently, a late-time dynamics of the corresponding QFT in Friedmann-Lemaitre-Robertson-Walker Universe. We identify DFPs that are perturbatively stable, and those that are perturbatively unstable, computing the spectrum of the quasinormal modes in the corresponding holographic dual. We further demonstrate that a stable DFP can be unstable non-perturbatively, and explain the role of the entanglement entropy density as a litmus test for a non-perturbative stability. Finally, we demonstrated that a driven evolution might not have a fixed point at all: the entanglement entropy density of a system can grow without bounds. [ABSTRACT FROM AUTHOR]

We study the anisotropic properties of dynamical quantities: direct current (DC) conductivity, butterfly velocity, and charge diffusion. The anisotropy plays a crucial role in determining the phase structure of the two-lattice system. Even a small deviation from isotropy can lead to distinct phase structures, as well as the IR fixed points of our holographic systems. In particular, for anisotropic cases, the most important property is that the IR fixed point can be non-AdS2 × ℝ2 even for metallic phases. As that of a one-lattice system, the butterfly velocity and the charge diffusion can also diagnose the quantum phase transition (QPT) in this two-dimensional anisotropic latticed system. [ABSTRACT FROM AUTHOR]

Holevo information is an upper bound for the accessible classical information of an ensemble of quantum states. In this work, we use Holevo information to investigate the ensemble theory interpretation of quantum gravity. We study the Holevo information in random tensor network states, where the random parameters are the random tensors at each vertex. Based on the results in random tensor network models, we propose a conjecture on the holographic bulk formula of the Holevo information in the gravity case. As concrete examples of holographic systems, we compute the Holevo information in the ensemble of thermal states and thermo-field double states in the Sachdev-Ye-Kitaev model. The results are consistent with our conjecture. [ABSTRACT FROM AUTHOR]

In this paper, we discuss the quality of holograms based on the calculation of the modulation depth. It's shown that the terahertz (THz) pulsed vortex beams play a vital role in holography filed, where two lasers with frequency difference have used. The THz vortex beams give new regions of larger frequency detuning and an important value of the modulation depth and fringe contrast (MDFC ratio) for obtaining the best holograms contrary to the Gaussian beams for which the best holograms are realized for small frequency detuning. The particular cases such as, Gaussian beam and single cycle pulses are deduced from our result. Numerical simulations are also presented to study the dependence of the MDFC ratio on the frequency detuning for THz vortex beams and Gaussian beams. This research could be beneficial in holographic interferometry, and it will firmly establish as a tool for scientific and engineering studies. [ABSTRACT FROM AUTHOR]

Tidal deformation of neutron star with multiquark core is calculated using nuclear and multiquark equations of state. The equation of state of the multiquark phase from the holographic Sakai-Sugimoto (SS) model is relatively stiff in the low density region and becomes softer at high densities. The values of Love number and dimensionless deformation parameter, k 2 and Λ , are found to be within the physically viable range under the present constraints. Radial pulsation frequencies of the multiquark core for n = 0 - 5 modes are calculated for the entire mass range. For M core ≃ 2 M ⊙ , the fundamental-mode frequency is approximately 2.5 kHz for the energy density scale ϵ s = 23.2037 GeV/fm 3 of the holographic SS model, this frequency is proportional to ϵ s . [ABSTRACT FROM AUTHOR]

In this paper we compare two implementations of the holographic technique for recording long, nonlinear, elastic waves of low amplitude in solid polymer waveguides: classical holographic interferometry and digital holography. Both implementations are realized in transmission configuration, with recording in the off-axis schematic. The advantages and disadvantages of these implementations are discussed as applied to the investigation of the evolution of shock waves and strain solitons in transparent solid waveguides. [ABSTRACT FROM AUTHOR]

Hydrogel-based holographic sensors consist of a holographic pattern in a responsive hydrogel that diffracts light at different wavelengths depending on the dimensions and refractive index changes in the material. The material composition of hydrogels can be designed to be specifically responsive to different stimuli, and thus the diffraction pattern can correlate with the amount of analyte. According to this general principle, different approaches have been implemented to achieve label-free optical sensors and biosensors, with advantages such as easy fabrication or naked-eye detection. A review on the different approaches, sensing materials, measurement principles, and detection setups, and future perspectives is offered. [ABSTRACT FROM AUTHOR]

We employ an analytic solution of a magnetized Einstein–Maxwell-dilaton gravity model whose parameters have been determined so that its holographic dual has the most similarity to the confining QCD-like theories. Analyzing the total potential of a quark–antiquark pair, we are able to investigate the effect of an electric field on different phases of the background which are the thermal AdS and black hole phases. This is helpful for better understanding of the confining character and the phases of the system. We find out that the field theory dual to the black hole solution is always deconfined, as expected. However, although the thermal AdS phase generally describes the confining phase, for quark pairs parallel to B (longitudinal case) with B > B critical the response of the system mimics the deconfinement, since there is no IR wall in the bulk and the critical field E s = 0 , as is the case for the deconfined phase. We moreover observe that in the black hole phase with sufficiently small values of μ and in the thermal AdS phase, for both longitudinal and transverse cases, the magnetic field enhances the Schwinger effect, which can be termed as the inverse magnetic catalysis (IMC). This is deduced both from the decrease of critical electric fields and decreasing the height and width of the total potential barrier the quarks are facing with. However, by increasing μ to higher values, IMC turns into magnetic catalysis, as also observed from the diagram of the Hawking–Page phase transition temperature versus B for the background geometry. [ABSTRACT FROM AUTHOR]

The paper shows that orthogonal Legendre polynomials in the interval [– 1, 1] can be effectively used to filter noisy signals, including filtering interferograms and phase maps in digital holographic interferometry. They can also be used to effectively approximate harmonic signals, and the approximation accuracy increases with the number of polynomials used. Filtering is based on the use of the optimal number of Legendre polynomials when approximating the signal. It is impractical to filter directly digital holograms and phase maps, since in this case it is necessary to use several hundred polynomials, which significantly increases the time of numerical calculations. Therefore, in digital holographic interferometry, it is necessary to filter directly the field amplitudes calculated from the digital hologram. Interferograms and phase maps can be calculated using filtered field amplitudes for different states of the object under study. If for the real or imaginary part of the signal the minimum distance between adjacent local minima (maxima) is equal to ∆l, then for a satisfactory approximation of such a signal by Legendre polynomials, 6/∆l polynomials are required. The efficiency of filtering by Legendre polynomials is higher if the noise signal contains harmonic components with a frequency greater than the frequency of the useful signal. [ABSTRACT FROM AUTHOR]

This research paper is focused on the development of a digital holography system for simultaneous dual-resolution measurements. Digital holography has been widely used for deformation measurements and non-destructive testing (NDT) due to its advantages of high sensitivity, high accuracy, and whole-field, non-touch measurements. A traditional test only has one spatial resolution, which can cause a big deformation to be indistinguishable or minor defects to be ignored. Both large and small fields of view should be observed to reach a multi-spatial resolution measurement. Usually, multiple separate tests are used to observe the different sized fields of view, resulting in higher costs and longer required testing times. Furthermore, these tests may not be repeatable in some cases. This paper presents research on a novel digital holography system that achieves dual spatial resolution measurements simultaneously by testing different-sized fields of view with a single camera. The novel system has two optical channels with two optical layouts of holography to measure deformation. By changing the combined focus length, the two holographic setups have different fields of view, i.e., one has a large and the other has a small field of view. To realize a simultaneous test, the polarization technique is used to avoid cross-interference between the two optical layouts. Finally, spatial carrier fringes with different orientations are introduced into the two holographic setups by appropriately adjusting the reference beam of each setup. The different oriented spatial carrier fringes enable the spectrums of the two interferograms to be separated after a FT (Fourier transform) and the phase distributions of the two interferograms can be extracted and separated by windowing the spectrum to perform an IFT (inverse Fourier transform). The phase distributions can then be used to analyze and calculate the deformations. The experiment using this system is described in this paper and the practicability of this method is verified by the obtained experimental results.

We received contributions from leading researchers across the globe on all the important facets of holography technologies with a total of 85 authors. Holography technologies have been rapidly evolving in the recent years due to surprising crossover of concepts and methods across different fields. One of the significant aspects of this special issue is the roadmap type articles on two main branches of holography and imaging, namely incoherent digital holography (IDH) [[1]] and chaos-inspired imaging technologies (CI SP 2 sp -Tech) [[2]]. [Extracted from the article]

A method of digital holographic interferometry and an automated laboratory unit developed to determine the parameters of a nonthermal plasma jet in a pulsed mode are proposed. The peculiarities of synchronizing the recording devices with the plasma pulses are discussed. The results of the plasma pulse detection and the phase maps corresponding to the refractive index variation are presented. [ABSTRACT FROM AUTHOR]

Isothermal mutual diffusion coefficients (interdiffusion coefficients) were measured for K2SO4(aq) at 298.15 ± 0.005 K, at numerous concentrations ranging from dilute solutions to near saturation (0.59648 mol·dm–3; 0.61349 mol·kg–1) under free diffusion boundary conditions, using high precision Rayleigh interferometry. Under the experimental conditions these diffusion coefficients are on the volume-fixed reference frame Dv. Two series of experiments were performed, the first using the traditional experimental approach with a mercury lamp source and with the interference patterns being recorded on glass photographic plates, and the second with a He–Ne laser light source and computerized data acquisition using a photodiode array. The results from both series of experiments are in excellent agreement, and generally yield diffusion coefficients precise to at least 0.002 × 10–9 m2·s–1 (0.15% to 0.19%) and in most cases to 0.001 × 10–9 m2·s–1 (0.07% to 0.1%). These experiments also yield accurate values of the refractive index differences for the solution pairs used in the diffusion experiments. The new diffusion coefficients are compared to two sets of published values of diffusion coefficients for K2SO4(aq) which are somewhat discrepant from each other. This study extends and complements our earlier work on the diffusion coefficients of the most common brine salts: NaCl(aq), KCl(aq), MgCl2(aq), CaCl2(aq), Na2SO4(aq),]MgSO4(aq), NaHCO3(aq), and KHCO3(aq) at 298.15 K. [ABSTRACT FROM AUTHOR]

Metal–insulator–metal (MIM) nanocavity, as a lossy Fabry–Pérot (FP) scheme, has been widely studied for color filter and perfect absorber functionality, which can be integrated into functional photonic devices. However, such triple‐layered MIM still lacks the ability to induce multiple intensity levels for meticulous grayscale imaging because of strong spectral sensitivity to cavity thickness variation. Moreover, the MIM stack remains unexplored to multiplex a near‐field nanoprinting and holographic imaging because it is challenging to break the mutual dependence relation between the intensity and phase shift. Herein, a new film stack of dual‐Fabry–Pérot (DFP) nanocavity is proposed to create triple‐fold freedom in light modulations: intensity, phase shift and operation wavelength, which can be respectively modulated by the top/bottom/total cavity length. By spatially arranging the stepwise nanocavities, the designed DFP pattern can show multiplexing dual‐channel imaging, which encrypts/conceals a grayscale nanoprinting image and simultaneously projects a far‐field holographic image. Such DFP strategy allows for new possibility of independent light modulation and creates new dimensional degree of freedom for thin‐film nanocavity. The proposed functional DFP strategy enriches the subwavelength building block design for metasurfaces and thin‐film stacks, which would promisingly empower advanced applications in information multiplexing, imaging encryption/concealing, and many other related fields. [ABSTRACT FROM AUTHOR]

The diffraction of light by reflective holographic gratings in a layer placed between the coating and the substrate having refractive indices different from the average refractive index of the inserted layer is investigated. Significant differences between the reflection and transmission coefficients of the light diffracted on such a holographic grating with a change in the modulation amplitude of the refractive index of the layer, and the reflection and transmission coefficients of reflection gratings in matched structures are established. It is shown that at a large width of the layer in which the reflective holographic grating is located, there is a significant rotation of the plane of polarization of reflected and transmitted diffracted waves with a change in the modulation amplitude of the layer, caused by Fresnel reflection of light at the layer boundaries. [ABSTRACT FROM AUTHOR]

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As metals form the backbone of many engineering structures including bridges and buildings, the detection of their mechanical deformation is of technological importance. Several optical techniques such as holographic interferometry, speckle interferometry, and digital image correlation have been developed to map the surface strains and displacements of various materials. However, these techniques have stringent requirements for stability and repeatability, which limit their application outside the laboratory. Herein, a colorimetric method for detecting mechanical deformation in metals based on the color change in an attached mechanochromic sensor is proposed. This study shows that a mechanically adaptable thin‐film sensor bonded to a block of metal can not only visualize the surface strain of the metal but also quantitatively measure it. The spatial distribution of the strain field can be mapped with high resolution by capturing the sensor image using a smartphone and analyzing its red, green, and blue components. This colorimetric method is applicable in both indoor and outdoor environments and can also be effective for detecting cracking or cleavage in rigid bodies. [ABSTRACT FROM AUTHOR]

The results of a study of a plasma jet of atmospheric-pressure helium driven by a capacitive discharge using sine and pulsed modes of excitation are presented. The homogeneous discharge of a multi-channel plasma jet at gas temperature of 34 °C and helium flow rate of 0.5 L/min was achieved with short pulse excitation. A digital holography method is proposed to estimate a basic plasma parameter, i.e., its electron concentration. An automated digital holographic interferometry set-up for the observation and study of a nonthermal plasma jet in a pulse mode is developed and described. The synchronization features of recording devices with the generation of plasma pulses are considered. The electron concentration of the plasma jet is also estimated. The disadvantages of the proposed technique and its further application are discussed. [ABSTRACT FROM AUTHOR]

This paper presents the results of holographic studies for angular contact rolling ball bearings of gas turbine engines. From these studies, the technical condition of angular contact ball rolling bearings was diagnosed and the cause of the defect—rupture of the cage's side connecting strip, was determined. [ABSTRACT FROM AUTHOR]

In this work, we describe the capabilities of Magnonic Holographic Memory (MHM) for parallel database search and prime factorization. MHM is a type of holographic device, which utilizes spin waves for data transfer and processing. Its operation is based on the correlation between the phases and the amplitudes of the input spin waves and the output inductive voltage. The input of MHM is provided by the phased array of spin wave generating elements allowing the producing of phase patterns of an arbitrary form. The latter makes it possible to code logic states into the phases of propagating waves and exploit wave superposition for parallel data processing. We present the results of numerical modeling illustrating parallel database search and prime factorization. The results of numerical simulations on the database search are in agreement with the available experimental data. The use of classical wave interference may results in a significant speedup over the conventional digital logic circuits in special task data processing (e.g., √n in database search). Potentially, magnonic holographic devices can be implemented as complementary logic units to digital processors. Physical limitations and technological constrains of the spin wave approach are also discussed. [ABSTRACT FROM AUTHOR]