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Beam scanning antenna brings new opportunities to reduce the data collision of multi-node communication in the Internet of Things (IoT). This paper proposes a new type antenna design scheme that can be used for IoT relay communication. A programmable beam scanning antenna without phase shifters operating in the X-band is designed to evaluate the feasibility of this scheme. The integrated design of excitation source and phasemodulated structure greatly reduces the profile of the antenna and improves the integrated degrees of freedom with other equipment. By switching the state of the PIN diode loaded on each element, different radiators can be selected and the direction of current polarization on elements can be adjusted to change the radiation phase. Furthermore, the diode states are encoded by the holographic antenna theory and controlled by the FPGA controller to realize programmable beam scanning. One element, two-element and 1-D array containing 32 elements are fabricated and measured. Experimental results are in good agreement with the simulation data. The operating bandwidth is 7.5% at 10GHz while the beam scanning range of the array is -60∘ 60∘, with a good scanning accuracy and stability. The proposed low-profile beam scanning antenna can provide stable communication services to multiple users and smart devices as a new type of beam scanning array antenna solution for the IoT application, which is beneficial to this field.

Holographic structured illumination combined with optogenetics enables patterned stimulation of neurons and glial cells in an intact living brain. Moreover, in vivo functional imaging of cellular activity with recent advanced microscope technologies allows for visualization of the cellular responses during learning, emotion and cognition. Integrating these techniques can be used to verify the link between cell function and behavior output. However, there are technical limitations to stimulate multiple cells with high spatial and temporal resolution with available techniques of optogenetic stimulation. Here, we summarized a two-photon microscope combined with holographic system to stimulate multiple cells with high spatial and temporal resolution for living mice and their biological application.

A liquid crystal-based beam-steering leaky-wave holographic antenna is designed with decoupling structure. Since the distance between elements in holographic antennas is inevitably small (< λ /5), the mutual coupling is strong and should be compensated for the accurate implementation of the excitation amplitude and phase of each element. The performance degradation of a holographic antenna due to mutual coupling is estimated and a decoupling structure is proposed, fabricated, and inserted into the designed antenna. The operating principle of the decoupling structure is explained with circuit model and the simulation confirms the enhanced gain and sidelobe performance when steered from -60° to 60° in 20° intervals. Compared to the antenna without the decoupling structure, the maximum improvement of the gain and the sidelobe level are 3.93 dB and 7.7 dB, respectively, in the simulation. The experimental results are consistent with the simulation results.

Holographic acoustic field has shown great potential for non-contact robotic manipulations of millimeter or sub-millimeter size objects to effectively deliver acoustic power. The latest technology for generating dynamic holographic acoustic field is through phased transducer array, where relative phases of emitted acoustic waves from transducers are independently controlled to modulate the acoustic interference field. While the forward kinematics of a phased array based robotic manipulation system is simple and straightforward, the inverse kinematics (i.e., the mapping from a given holographic acoustic field to array phases for control purpose), however, is mathematically non-linear and unsolvable, presenting challenges in developing wider applications of holographic acoustic field for robotic manipulation. Considering, thus far, there are still no effective solutions reported, the authors put intensive efforts to solve this problem using a machine learning approach, which we refer to as AcousNet. Experimental results demonstrate the effectiveness of the proposed method for dynamic holographic acoustic field generation from phased transducer array.

As a prominent candidate to cope with both device integration and miniaturization, multifunctional metadevices have attracted increasing interest recently. However, suffering from several demerits, conventional multifunctional devices that could not meet practical demands. In this paper, we elaborate on a single-layer transmissive all-dielectric meta-lens platform that can flexibly manipulate beams by pluggable phase elements over a broad millimeter-wave regime. The pluggable element of the meta-lens platform is able to provide a full 2π transmission phase coverage together with a high transmission coefficient. The elements are encoded into 36 phase modules as a phase library. The designed phase modules can be re-assembled that span 2π uniformly to reconstruct distinct functions, due to their dynamic pluggable feature. To verify its flexible assembly and efficient phase modulation, the meta-lens platform with different arrangements of phase modules is assembled and demonstrated in the experiment, which is in good agreement with theoretical and simulation analyses. Owing to the properties of flexible assembly, broad bandwidth, and high efficiency, the proposed meta-lens platform paves the way for potential applications in millimeter-wave regimes such as beamforming, computer-generated hologram, and other complex demands that involve phase manipulations.

Transcranial ultrasound therapy has become a non-invasive method for treating neurological and psychiatric disorders, and studies have further demonstrated that multi-target transcranial ultrasound therapy is a better solution. At present, multi-target transcranial ultrasound therapy in small animals can only be achieved by the multi-transducer or phased array. However, multiple transducers may cause spatial interference, and the phased array system is complicated, expensive, and especially unsuitable for small animals. This study is the first to design and fabricate a miniature acoustic holography lens for multi-target transcranial ultrasound therapy in rats. The acoustic holographic lens, working at a frequency of 1.0 MHz, with a size of 10.08 mm × 10.08 mm and a pixel resolution of 0.72 mm, was designed, optimized, and fabricated. The dual-focus transcranial ultrasound generated based on the lens was measured; the full width at half maximum (FWHM) of the focal spots in y-direction were 2.15 and 2.27 mm, respectively, and in z-direction were 2.3 and 2.36 mm, respectively. The focal length was 5.4 mm, and the distance between the two focuses was 5.6 mm, close to the desired values of 5.4 mm and 6.0 mm, respectively. Finally, the multiple-target blood-brain barrier opening in rats' bilateral secondary visual cortex (mediolateral area, V2ML) was demonstrated using the transcranial ultrasound therapy system based on the lens. These results demonstrate the good performance of the multi-target transcranial ultrasound therapy system for small animals, including high spatial resolution, small size, and low cost.

In this letter, the cylindrical modal filtering is presented for digital holographic reconstruction (DHR) phase-less near-field (NF) measurement. The DHR phase-less NF facility can reconstruct the complex field of the antenna under test (AUT) by measuring only the intensity of the interference field on the AUT and reference antenna in one NF scanning plane. In addition to the retrieved AUT field, some unwanted items also exist in the reconstructed field. Hence, advanced filtering method is essential to extract the retrieved AUT field from the reconstructed field. In previous work, it is achieved by the back-projected (BP) filtering. In this work, the BP modal filtering is utilized to further improve the accuracy of the DHR phase-less NF measurement. To enhance the adequate modal separation between the desired and unwanted terms, the reconstructed field is firstly BP to the aperture plane, then represented with orthogonal cylindrical modes. Finally, the AUT field is extracted by twice modal filtering to remove the disturbances on two orthogonal directions. The simulation and experiment results indicate that compared with the results by the BP filtering, the accuracy of the DHR phase-less NF measurement has been improved 50% in valid angle by adopting the BP modal filtering.

This paper describes the secure storage and matching of latent fingerprints using phase shifting digital holography. A phase shifting digital holographic system is proposed for imaging of latent fingerprints, which can be applied in the criminal investigation field. Digital holography is one of the accurate and fast technique for measuring 3D information, by acquiring both amplitude and phase information from the object. Digital holography uses a Charge-Coupled Device (CCD) to record the interference pattern. In digital holography, the reconstructed image unavoidably contains the conjugate image and the zeroth order beam, resulting in low resolution. This problem can be overcomed by using phase shifting digital holography. Phase shifting digital holography is a technique by which multiple holograms are taken corresponding to the various phase differences between the object beam and the reference beam. One of the most secure storage methods is digital holographic data storage which provides a credible way in the fingerprint acquisition in the criminal investigation field. The phase shifting digital holograms of the latent fingerprint are acquired and then numerically reconstructed. The reconstructed fingerprint is then compared with the database after further processing to find whether it is a match or no match. The investigations have been conducted through experiments and computer simulations. The parameters used for analyzing the performance of the system are False Matching Rate (FMR), False Non-Matching Rate (FNMR) etc. This system shows a remarkable performance improvement over digital holographic techniques. The method can be explicitly used in forensic applications.

The surface quality verification of mechanical components is an essential activity in many applications where surface performance plays an important role in the functional behaviour of the part. Although many of the verification techniques commonly employed are based on the use of contact roughness profilometers, there are some limitations related to the morphological filtering effect associated to the stylus tip radius, as well as the difficulty in using these type of styli to carry out on-machine surface verification. The use of non-contact digitizing techniques helps to overcome some of these drawbacks, although the verification of surface quality using these non-contact systems still requires the development of scanning and data processing procedures similar to those described in the international standards for contact probing techniques. This work analyses the use of a non-contact sensor, based on Conoscopic Holography and integrated in a 3-axis machining centre, applied to the verification of the surface roughness of parts machined by face and cylindrical milling processes. After the calibration of the integrated system, a high-frequency noise filtering procedure specifically designed for roughness verification is proposed. The results demonstrate the feasibility of the system for verifying surface roughness grades from N5 to N12 in the two milling processes. Finally, specific filtering recommendations for each roughness grade of both milling processes as well as a surface verification procedure are provided.

Integrating compressed sensing (CS) with millimeter-wave (mmW) holography has shown great potential to achieve lightweight onboard hardware, low sampling ratio, and high-speed sensing. However, conventional CS-driven algorithms are always limited by nontrivial adjusting of parameters and excessive computational cost caused by plenty of iterations. To address this problem, we propose a lightweight model-based deep learning framework (LFIST-Net) for mmW 3-D holography, by combining the interpretability of fast iterative shrinkage-thresholding algorithm (FISTA) and tuning-free merit of data-driven deep neural network. First, the single-frequency (SF) holographic imaging technique is integrated into FISTA, which serves as the sensing kernels, to avoid large-scale matrix multiplications. Subsequently, the kernel-based FISTA (KFISTA) is mapped into layer-fixed and parameter-learnable LFIST-Net, whose weights are relaxed to be layer-varied. The updating of key parameters in LFIST-Net, including step sizes, thresholds, and momentum coefficients, are regularized by soft-plus function to ensure the non-negativity and monotonicity. As for 3-D holography implementation, the ``1-D + 2-D'' scheme is adopted, where the matched filtering (MF) and well-trained LFIST-Net are used for range focusing and reconstructions of azimuth slices. Without losing efficiency, the range-focused subechoes are processed parallelly in 3-D cube form. Experiments, including both simulated and measured tests based on a commercial mmW radar, prove that LFIST-Net is capable of reconstructing the imaging scene precisely. In particular, in near-field mmW 3-D holography tests, both numerical and visual results demonstrate LFIST-Net yields compelling reconstruction performance while maintaining high computational speed compared with MF-based, conventional CS-driven, and network-based methods.

Recently, more interest in the different plenoptic formats, including digital holograms, has emerged. Aside from other challenges that several steps of the holographic pipeline, from digital acquisition to display, have to face, visual quality assessment of compressed holograms is particularly demanding due to the distinct nature of this 3D image modality when compared to regular 2D imaging. There are few studies on holographic data quality assessment, particularly with respect to the perceptual effects of lossy compression. This work aims to study the quality evaluation of digital hologram reconstructions presented on regular 2D displays in the presence of compression distortions. As there is no established or generally agreed on compression methodology for digital hologram compression on the hologram plane with available implementations, a set of state-of-the-art compression codecs, namely, HEVC, AV1, and JPEG2000, were used for compression of the digital holograms on the object plane. Both computer-generated and optically generated holograms were considered. Two subjective tests were conducted to evaluate distortions caused by compression. The first subjective test was conducted on the reconstructed amplitude images of central views, while the second test was conducted on pseudovideos generated from the reconstructed amplitudes of different views. The subjective quality assessment was based on mean opinion scores. A selection of objective quality metrics was evaluated, and their correlations with mean opinion scores were computed. The VIFp metrics appeared to have the highest correlation.

Publisher Copyright: Author We present design, simulation, and experimental characterization of dual-band frequency-diverse holograms for distributed beamforming. The holograms operate in the 50-75 GHz (WR-15) and 220-330 GHz (WR-3.4) bands for millimeter-and submillimeter-wave imaging. The holograms are designed to create a dispersive field in the region of interest (RoI) located 600 mm from the aperture. The holograms lie in the front end of an imaging setup and modulate the phase of the incident collimated beam from a parabolic mirror. The distributed beamforming enables interrogation of the RoI so that the measured reflection through the dispersive propagation path conveys the spatial information of the target. Different phase modulation schemes are evaluated, and two prototype holograms are manufactured. The dispersive operation and efficiency of the hologram are characterized with both simulations and measurements. The frequency diversity of the holograms is quantified using singular-value decomposition and spatial-spectral correlation coefficient methods. The results identified a design frequency of 120 GHz, a phase quantization step of π/2 radians, and an added phase of 1.9π radians as a good dispersion-efficiency compromise. A fully connected neural network is trained to localize a corner-cube reflector in the RoI illuminated by the hologram. The localization accuracy follows the diffraction-limited resolution and confirms the best performance for the hologram considered optimal in the design metrics.

This work investigates the astigmatic dual-beam interferometric particle imaging (ADIPI) to enable the measurement of the three-dimensional (3D) spatial position and particle size of spherical opaque particles. A general theoretical model based on the generalized Huygens-Fresnel integral and the ray transfer matrix model is established to characterize ADIPI signal, revealing the orientation and spacing of typical ADIPI fringes relating to the depth position and size. The model is applied to study the effects of several parameters, such as the focal length of cylindrical lens, the focal length of spherical lens and the distances between the elements in the optical system, on the relationship between the inclination angle of fringes and depth position by theoretical simulation. Experiments of ADIPI, incorporating dual-view digital inline holography (DIH), is performed to demonstrate the utility of ADIPI in the measurement of opaque spherical particles. Through the analysis of the general ADIPI signal based on two-dimensional Fourier transforms, 3D position and the particle size are obtained. The results of ADIPI, in both of the depth position and size measuring, exhibit a high degree of consistency with DIH's, given the average relative deviations of 5% in size measuring and 1% in depth position, respectively. As a new measurement approach, the ADIPI signal exists at arbitrary angle except the two laser beam axes, determining the flexibility of ADIPI configurations which facilitates its great prospect in opaque particles measurement, e.g., metal combustion, chip manufacturing, 3D metal printing.

Cryptography plays an important role in information security, which is widely applied in the various fields of society. Quantum cryptography has shown its great advantages in information security compared with the classical one. Two major directions of quantum cryptography are quantum key distribution (QKD) and quantum encryption, with the former focusing on secure key distribution and the latter focusing on encryption using quantum algorithms. In contrast to the well accepted success of the QKD, the development of quantum encryption is rather limited because of the difficulties of building up algorithms and the constructing the practical quantum computers. Here we propose a new scheme of quantum encryption based on high-dimensional entanglement holography. Firstly, we experimentally realize the quantum holography based on the high-dimensional orbital angular momentum (OAM) entanglement. Then, OAM-selective holographic scheme for quantum encryption is proposed and demonstrated. Our results show that introducing quantum entangled state into OAM holography makes the OAM holography possess infinite information channels and the transmission of information be absolute security in principle. Furthermore, decryption in the presence of strong noise is achieved. Our work opens up a new way to realize quantum information security.

Recently in nanophotonics, a rigorous evolution from passive to active metasurfaces has been witnessed. This advancement not only brings forward interesting physical phenomena but also elicits opportunities for practical applications. However, active metasurfaces operating at visible frequencies often exhibit low performance due to design and fabrication restrictions at the nanoscale. In this work, we demonstrate electrochemically controlled metasurfaces with high intensity contrast, fast switching rate, and excellent reversibility at visible frequencies. We use a conducting polymer, polyaniline (PANI), that can be locally conjugated on preselected gold nanorods to actively control the phase profiles of the metasurfaces. The optical responses of the metasurfaces can be in situ monitored and optimized by controlling the PANI growth of subwavelength dimension during the electrochemical process. We showcase electrochemically controlled anomalous transmission and holography with good switching performance. Such electrochemically powered optical metasurfaces lay a solid basis to develop metasurface devices for real-world optical applications.

This paper presents a simple, yet effective method for dynamic beamforming that can be readily realized by integrating a tunable binary Huygens' metasurface with a leaky-waveguide antenna. Heretofore, dynamic beamforming has been difficult to achieve owing to the challenges in attaining full 360 of dynamic phase tunability, while also independently controlling the local aperture amplitudes from zero to unity. In contrast, the hereby proposed method only requires 90 of dynamic phase tunability (with arbitrary transmission amplitudes), thereby significantly alleviating the stringent tuning requirements. In particular, the proposed method is obtained by leveraging the antenna-array and holography theories, and utilizing the idea of ‘virtual’ electric line sources. Based on full-wave simulations, we demonstrate the versatility of the proposed method through the designs of a Huygens'-metasurface-assisted leaky-waveguide antenna that generates various complex far-field patterns such as sector beams and Dolph-Chebyshev patterns.

Morphology measurement is essential for a better understanding of irregular particle dynamics. Digital holography of side scattering is applied to measure the morphology and 3D position of pulverized coal particles. The digital holographic recording of particle side scattering is modelled and the formula is verified by experiments. A side scattering holography system is established to record the hologram of pulverized coal particles. The hologram of particles with several scatterers has uneven chirp fringes which is mainly influenced by scatterer shape, while the hologram of particles with multiple scatterers is a superposition of single scatterer fringes with a speckle background which is influenced by both scatterer shape and location. The Moire pattern which appears easily in digital holography of side scattering is also analyzed. The proposed technique is validated by in-line holography and is proven to have an advantage in the identification of irregular particle morphological and surface features simultaneously.

In this paper, we obtain an anisotropic Bianchi type-II space–time with dark matter and modified holographic Ricci dark energy in the scale-covariant theory of gravitation. Exact solutions of the field equations are obtained by assuming (i) a negative constant value of the deceleration parameter, (ii) the component [Formula: see text] of the shear tensor [Formula: see text] is proportional to the mean Hubble parameter, and (iii) the gauge function [Formula: see text] is proportional to a power function of the average scale factor. We have also discussed some important physical aspects of the model, which is in agreement with the modern cosmological observations.

Cell studies play an important role in the basis of studies on cancer diagnosis and treatment. Reliable viability assays on cancer cell studies are essential for the development of effective drugs. Lens-free digital in-line holographic microscopy has become a powerful tool in the characterization and viability analysis of microparticles such as cancer cells due to its advantages such as high efficiency, low cost, and flexibility to integrate with other components. This study is designed to perform viability tests using fractal dimensions of alive and dead cancer cells based on digital holographic microscopy and machine learning. In the in-line holography configuration, a microscopy assembly consisting of inexpensive components was built using an LED source, and the images were reconstructed using computational methods. The standard US Air Force Resolution Target was used to evaluate the capability of our imaging setup then holograms of stained cancer cells were recorded. To characterize individual cells, 19 different rotational invariant fractal dimension values were extracted from the images as features. An artificial neural network technique was employed for the classification of fractal features extracted from cells. The artificial neural network was compared with four other machine learning techniques through five different classification performance measures. The empirical results indicated that artificial neural networks performed better than compared classification techniques with accuracies of 99.65%. The method proposed in this paper provides a new method for the study of cell viability which has the advantages of high accuracy and potential for laboratory application.

In this study, we consider an holographic dark energy and dark matter interacting model in the Bianchi Type-V universe with a stretched exponential scale factor. We obtain the Hubble, shear, deceleration, and equation of state parameters based on the presented model and give the numerical solutions. We show that the anisotropy in the early universe plays an important role in the time evolution of the universe. Furthermore, we show that an interacting anisotropic model with stretched exponential scale factors can explain all epochs of the universe.

PURPOSE The purpose of this study was to develop and preliminarily test a radiotherapy system for patient posture correction and alignment using mixed reality (MixR) visualization. The write-up of this work also provides an opportunity to introduce the concepts and technology of MixR for a medical physics audience who may be unfamiliar with the topic. METHODS A MixR application was developed for on optical-see-through head-mounted display (HoloLens 2) allowing a user to simultaneously and directly view a patient and a reference hologram derived from their simulation CT scan. The hologram provides a visual reference for the exact posture needed during treatment and is initialized in relation to the origin of a radiotherapy device using marker-based tracking. The system further provides marker-less tracking that allows the user tofreely navigate the room as they view and align the patient from various angles. The system was preliminarily tested using both a rigid (pelvis) and nonrigid (female mannequin) anthropomorphic phantom. Each phantom was aligned via hologram and accuracy quantified using CBCT and CT. RESULTS A fully realized system was developed. Rigid registration accuracy was on the order of 3.0 ± 1.5 mm based on the performance of three users repeating alignment five times each. The lateral direction showed the most variability among users and was associated with the largest off-sets (approximately 2.0 mm). For nonrigid alignment, the MixR setup outperformed a setup based on three-point alignment and setup photos, the latter of which showed a difference in arm position of 2 cm and a torso roll of 6-7°. CONCLUSIONS MixR visualization is a rapidly emerging domain that has the potential to significantly impact the field of medicine. The current application is an illustration of this and highlights the advantages of MixR for patient setup in radiation oncology. The key feature of the system is the way in which it transforms nonrigid registration into rigid registration by providing an efficient, portable, and cost-effective mechanism for reproducing patient posture without the use of ionizing radiation. Preliminary estimates of registration accuracy indicate clinical viability and form the foundation for further development and clinical testing.

The development of technology has now begun to shift to society 5.0, this technology has helped many human activities. The development of technology is also followed by the development of games, games in holographic form have been made by several developers, however, there are not many games in the holographic form that are marketed and played by many players. Hologram technology is a technology that is starting to develop at this time. There have been several games made from holograms, in fact, there are already tools to view or display holographic shapes. This paper explains that the creation and development of games using holographic technology has been around for decades. The development of the times has slowly begun to expand and develop knowledge about hologram technology by making hologram games and adding or developing ways of interacting with these hologram games. Keywords—Hologram Game Technology, 3D Hologram, Hologram for Game, Modern Technology

Holography has been extensively studied as a vital method to tailor wavefronts of electromagnetic waves. Compared to conventional holography, metasurface-based holography generally presents the adv...

A volumetric display generates a graphics that can be viewed from 360$$^{\circ }$$ ∘ by representing the 3D information of an object as voxels in physical space. However, the natural properties of physical objects, such as 3D information and colors, and the seamless relationships between graphics and humans make it difficult to implement such displays. Here, we introduce a novel system that combines the spatial generation of femtosecond-laser-excited emission points using computer-generated holograms and beam scanning with the drawing space separation method. We demonstrate the drawing of volumetric graphics that can be color-expressed in voxel units in the air. This system enables the drawing of volumetric graphics in the air, accurate color representations, and robust graphics that are not destroyed by contact with users or objects. It also lays the foundation for the implementation of future volumetric displays.

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.

5G and beyond mobile systems target a plethora of emerging industrial and entertainment verticals that incur extra overhead to the network. These verticals are characterized by vigorous, continuous, and conflicting requirements that make the desired system's mission strenuous and more challenging. These verticals, such as autonomous driving, will accommodate immersive services, including virtual reality/augmented reality (VR/AR) and Holography services. Immersive services, in particular, have strict requirements for latency, throughput, and positioning. This article discusses VR-based remote services' potential, which occupies an important place among immersive services such as remote surgery, remote space control, and remote driving of Unmanned Aerial Vehicles (UAVs) or cars. Such services require an ultra-low Glass-to-Glass latency to avoid any failure and accidents when remotely controlling devices. We evaluate an immersive remote control service from the end-to-end communication perspectives using different camera devices that stream real-time 360° videos to a VR Head Mounted Device (HMD). The obtained results demonstrate the challenges of such service and the need for more advanced and optimized techniques, devices, and protocols to achieve less than 20 ms of Glass-to-Glass latency.

The two-photon fluorescence imaging depth has been significantly improved in recent years by compensating for tissue scattering with wavefront correction. However, in most approaches the wavefront corrections are valid only over a small sample region on the order of 1 to 10 µm. In samples where most scattering structures are confined to a single plane, sample conjugate correction geometries can increase the observable field to a few tens of µm. Here, we apply a recently introduced fast converging scheme for sensor-less scattering correction termed “Dynamic Adaptive Scattering compensation Holography” (DASH) in a sample conjugate configuration with a high pixel count nematic liquid crystal spatial light modulator (LC-SLM). Using a large SLM allows us to simultaneously correct for scattering at multiple field points, which can be distributed over the entire field of view provided by the objective lens. Despite the comparably slow refresh time of LC-SLMs, we achieve correction times on the order of 10 s per field point, which we show is sufficiently fast to counteract scattering at multiple sites in living mouse hippocampal tissue slices.

The boundary element method- (BEM-) based free field recovery technique (FFRT) has been proposed to recover the free field radiated by an arbitrarily shaped source from the mixed field that would be measured in a noisy environment. However, that technique requires that the boundary integral equation should be established on an enclosed hologram surface surrounding the source, which means that the hologram surface should be discretized into elements and the measurement points should be located on the nodes of the elements. For large-scale or mid-high frequency problems, it makes the total number of measurement points huge since it should obey the criterion of more than six elements per wavelength, which put forward very high requirements for holographic data measurement. To overcome this problem, a more flexible BEM-based FFRT without the restriction on the locations of measurement points is proposed in this study. In virtue of this, a three-dimensional scanning measurement method can be applied to acquire holographic data with high efficiency. The effectiveness of the proposed method is validated by two numerical simulations and an experiment.

Infrared metasurface, especially that having a working range covering wavelengths from 0.75 to 25 μm, has been exploited as a revolutionary tool to manipulate the properties of electromagnetic waves owing to its potential applications in military and civilian fields. It owns the capacity to steer electromagnetic waves within subwavelength scale, with full degrees of freedom such as phase, amplitude and polarization, allowing the development of a number of planar meta-devices including the metalens, hologram, wave-plate and polarimeter. In particular, polarization, which determines the interaction of electromagnetic waves with matter, is important in almost every area of science. However, conventional materials for infrared polarization control inevitably introduce extra optical components and bulky configurations, hindering future miniaturization and integration. Moreover, compared with their short wavelength counterparts, polarization nanodevices in the infrared band and especially those in the long-wavelength infrared region have been far less explored due to the loss of material and immature fabrication techniques. Here, we review recent progress in the development of infrared metasurfaces in terms of generating, manipulating and detecting the polarization on standard and higher-order Poincare spheres. The principles, typical strategies and emerging applications of these processes are introduced. We also discuss the challenges and outlook of future developments in this emerging field.

Reconstruction of in-line holograms of unknown objects in general suffers from twin-image artifacts due to the appearance of an out-of-focus image overlapping with the desired image to be reconstructed. Computer-based iterative phase retrieval algorithms and learning-based methods have been used for the suppression of such image artifacts in digital holography. Here we report an all-optical hologram reconstruction method that can instantly retrieve the image of an unknown object from its in-line hologram and eliminate twin-image artifacts without using a digital processor or a computer. Multiple transmissive diffractive layers are trained using deep learning so that the diffracted light from an arbitrary input hologram is processed all-optically, through light-matter interaction, to reconstruct the image of an unknown object at the speed of light propagation and without the need for any external power. This passive all-optical processor composed of spatially-engineered transmissive layers forms a diffractive network, which successfully generalizes to reconstruct in-line holograms of unknown, new objects and exhibits improved diffraction efficiency as well as extended depth-of-field at the hologram recording distance. This all-optical hologram processor and the underlying design framework can find numerous applications in coherent imaging and holographic display-related applications owing to its major advantages in terms of image reconstruction speed and computer-free operation., Comment: 19 Pages, 5 Figures

In recent years, there has been an increasing need for larger screens and higher definition displays, while projectors are becoming smaller and cheaper. Furthermore, an ultra-short-throw projector that can display on a large screen while significantly reducing the distance between the projector and screen is being developed. However, ultra-short-throw projectors are required to be precisely aligned with the screen, and if the screen is not flat, the projected image becomes distorted. Therefore, geometric correction projection technology is attracting attention for projection on curtains and the walls of living rooms instead of screens for realizing the correction of distortion during projection with ultra-short-throw projectors, projection mapping, signage, etc. We focused on developing a hologram with perfect command of the ray. Conventional geometry-correction systems are expensive systems that require a personal computer and a camera. In this study, we developed a geometric correction method applying holographic ray direction control technology to control a holographic ray at a low cost and in real time. In this paper, we studied the exposure technology and proposed a ray-direction control technology that combines a scanning laser projector that uses a hologram and a micro electro mechanical systems mirror. We also proposed and demonstrated the basic principle of a holographic surface projector (HSP), which uses hologram geometry correction technology. Finally, we constructed a geometrically corrected hologram exposure system using a depth camera and conducted geometrically corrected projection experiments.

The paper presents a study of the formation of holographic diffraction gratings in thin films of chalcogenide glassy semiconductors. The recording process of holographic gratings at the argon-laser radiation wave length 488 nm and the process of chemical etching that enables the formation of а relief holographic grating are analysed. The optimum conditions for the formation of diffraction gratings in films of arsenic sulfide As2S3 are defined. It is shown that at the 488 nm wave length of an argon laser the optimum exposure comes to ∼5–8 J/cm2. At the recording stage a quasi-phase (relief-phase) grating is formed, with the diffraction efficiency on the order of a few per cent. Etching of the exposed sample with a solution of NaOH alkali in deionised water and isopropanol makes it possible to increase considerably the relief depth and to improve the diffraction efficiency of a thin diffraction grating approximately up to 20 % for the red spectral region, and to approach the maximal value ∼34 % for the near infra-red region. The results of the study considered look promising for the creation of relief holographic gratings which are essential in present-day optical instrument building (production of spectral devices, holographic sights, and the like).

We study the homogenous quenching processes in a holographic s+p model with reentrant phase transitions. We first realize the reentrant phase transition in the holographic model in probe limit and draw the phase diagram. Next, we compare the time evolution of the two condensates in two groups of numerical quenching experiments across the reentrant region, with different quenching speed as well as different width of the reentrant region, respectively. We also study the dynamical competition between the two orders in quenching processes from the normal phase to the superconductor phase., Comment: 19 pages, 9 figures

Sprays generated by atomization processes have been used in a wide range of fields. The size and spatial distribution of volumetric droplets in a spray are critical parameters in industrial applications. Astigmatic interferometric particle imaging (AIPI), an extension of the traditional interferometric particle imaging (IPI), is developed to simultaneously measure the size and 3D position of volumetric droplets in a sparse spray. Based on the generalized Huygens–Fresnel integral and the transfer matrix, the size and depth position of droplet can be respectively extracted from the fringe spacing and orientation of interferogram in AIPI. An AIPI setup is established to characterize droplets in a sparse spray generated by a nozzle with the AIPI calibration procedure adopted. The measured parameters by AIPI are compared with those obtained synchronously by digital inline holography, which is regarded as a standard measurement technique. Results show that the average deviation values of droplet size and depth position are respectively 3.8% and 6.8%. AIPI has been demonstrated with high accuracy in simultaneous 3D positions and size measurements.

This research explores the Tsallis holographic quintessence, k-essence, and tachyon models of dark energy in the modified f(R, T) gravity framework with Granda–Oliveros cutoff. We have analyzed the energy density through [Formula: see text]. We study the correspondence between the quintessence, k-essence, and tachyon energy density with the Tsallis holographic dark energy density in a flat FRW Universe. The reconstruction is performed for different values of Tsallis parameter δ in the region of ωΛ > –1 for the EoS parameter. This correspondence allows reconstruction of the potentials and the dynamics for the scalar field models, if we set some constraints for the model parameters, which describe the accelerated expansion of the Universe.

Holographic reconstructions of the sound field in the vicinity of a tied-down F-35 aircraft were achieved by applying multisource statistically optimized near-field acoustical holography to measure...

A highly dispersive, diffractive optical element is designed and realized for an extremely high spectral resolution spectroscopy for exoplanet telescope application. Our design uses an annular Fresnel hologram to transform incident starlight directly into a spectrogram. The recording of the hologram is accomplished using two spherical waves of different radius of curvature. The resultant hologram consists of an annular grating structure with a gradually shrinking period as a function of increasing radius. The variable period not only could bring the incoming star-light into focus, but also exhibits a large on-axis chromatic behavior. We demonstrate a dispersion of wavelength 430–700 nm over 190 mm on-axis distance, leading to a super fine spectral resolution 0.0266 nm at wavelength 515 nm for a detector size of 20 µm.

Radio technologies are appealing for unobtrusive and remote monitoring of human activities. Radar-based human activity recognition proves to be a success, for example, Project Soli developed by Google. However, it is expensive to scale up for multiuser environments. In this article, we propose a solution—the HoloTag system—which circumvents the multichannel-radar scaling problem through the use of a quasivirtual ultralow-cost UHF RFID array over which a holographic projection of its environment is measured and used to both localize and monitor the health of several targets. The method is first described in detail, before the image reconstruction process, employing known beamforming algorithms—Delay & Sum, and Capon—is shown and its scaling properties simulated. Then, the idiosyncrasies of the implementation of HoloTag using low-cost off-the-shelf hardware are explained, before its ability to simultaneously measure the breathing rates and positions of multiple real and synthetic targets with accuracies of better than 0.8 bpm and 20 cm is demonstrated.

The problem of fabrication of compact units for digital holography that are compatible with optical microscopes and the features and advantages of a two-component lens-in-lens interferometer in such units are considered. Optical design and aberration correction of such an interferometer that represents a compact module, have been carried out. A similar module can be used in systems for the analysis of micro-objects with a smooth distribution of the phase delay in biomedicine and industry.

If an optical hologram is broken into pieces, a virtual object can still be reconstructed from each of the fragments. This reconstruction is possible because each diffraction point emits waves that reach every point of the hologram. Thus, the entire object is encoded into each subset of the hologram. Analogous to the broken hologram, the use of undersampled seismic data violating the Nyquist-Shannon sampling theorem may still give a well-resolved image of the subsurface. A theoretical framework of this idea has already been introduced in the literature and denoted as holistic migration. However, the general lack of seismic field data demonstrations has inspired the study presented here. Since the optical hologram is diffraction-driven, we propose to employ diffraction-separated data and not conventional reflection data as input for holistic migration. We follow the original idea and regularly undersample the data spatially. Such a sampling strategy will result in coherent noise in the image domain. We therefore introduce a novel signal processing technique to remove such noise. The feasibility of the proposed approach is demonstrated employing the Sigsbee2a controlled data set and field data from the Barents Sea.

Measuring the distribution, characteristics and dynamics of marine microscale plankton and other particulate matter is essential to understand the vertical flux of elements in the marine environment. Digital holographic microscopy is a powerful approach for measuring these and studying their 3-D trajectories in a relatively large observation volume. This article demonstrates a compact, in-line digital holographic microscope that allows large-volume and high-resolution recording of marine particles through combining a continuous wave laser and a short exposure CMOS camera with efficient global shutters. A resolution of better than 10 μm is demonstrated in air and the minimum distinguishable size of targets recorded in water is approximately 20 μm. The maximum volumetric throughput of the setup is 1904 mL/s. The microscope can take motion blur free holograms of particles moving at up to 490 mm/s in theory, and has been tested in the ∼200-mm/s flowing water. The orientation of the measured volume improves the ability of digital holography in profiling sinking rates and active vertical migration. The system was tested onboard a research vessel to record a range of live plankton and other particles. The motion of some samples, including the sinking motion and swimming motion, was analyzed using custom developed image processing software. The experimental results show that the combination of high resolution and a large volume over which motion of sparse-distribution particles can be tracked, can improve the ability to differentiate between different types of marine particle and identify behaviors of live plankton.

In this letter, we present a holographic metasurface (HMS) based on an orthogonally discrete unit-cell. The proposed unit-cell possesses discrete surface impedance tuning abilities in two orthogonal directions, providing flexible beam formation as a scalar unit-cell and polarization control as a tensor unit-cell. Operation principle and design formulas for generating independently linearly polarized beams and circularly polarized beams using the orthogonal components are concluded. Two example antennas utilizing this HMS are measured to demonstrate the beam formation and polarization control abilities at 11.0 GHz. The first example antenna generates dual beams with independently linear polarizations whereas the second example antenna generates dual beams with independently circular polarizations. Our letter indicates that there exists a middle type of HMS between scalar and tensor HMSs.

In a classical metasurface-based holographic display system, a clear holographic reconstruction image can be obtained only in the back-focal-plane of the lens. However, when the receiving plane deviates from the focal plane, the reconstructed holographic image suffers from degradations that limit the quality of the images. Hence, we propose a novel metasurface-based holographic display to realize clearly continuous imaging within the specified position range by superimposing the meta-axilens phase. It can effectively relieve the alignment requirements of the imaging system. Firstly, the parameters and properties of all-dielectric meta-atom is analyzed. Then we compare and demonstrate two sets of metasurface-based optical elements (meta-axicon, meta-lens, and meta-axilens), made by silicon meta-atoms working at 610 nm. Furthermore, we show that the metasurface hologram with the axilens phase can form a series of the relatively clear holographic images away from the focal plane. Our proposal suggests a method to reconstruct holographic wavefront in different planes simultaneously, and one can find their application domain, such as 3D biological imaging, spectroscopy, optical information storage, and encryption.