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In this thesis, we explore the implications of a recent algorithm by Scott Aaronson and Jason Pollack showing that it is possible to reconstruct a bulk AdS geometry given contiguous entropies from a CFT on the boundary. We consider this in light of the area law/volume law phase transition in monitored circuit models, and show that volume law entanglement corresponds to the formation of large-scale structure in the bulk, while area law entanglement fails to do so. We also investigate behavior near the quantum critical point, finding preliminary evidence that a dual phase transition in the bulk may coincide with the formation of a nontrivial bulk geometry.

Video services are evolving from traditional two-dimensional video to virtual reality and holograms, which offer six degrees of freedom to users, enabling them to freely move around in a scene and change focus as desired. However, this increase in freedom translates into stringent requirements in terms of ultra-high bandwidth (in the order of Gigabits per second) and minimal latency (in the order of milliseconds). To realize such immersive services, the network transport, as well as the video representation and encoding, have to be fundamentally enhanced. The purpose of this tutorial article is to provide an elaborate introduction to the creation, streaming, and evaluation of immersive video. Moreover, it aims to provide lessons learned and to point at promising research paths to enable truly interactive immersive video applications toward holography.

The study, preservation and restoration of the cultural heritage objects of mankind are not only of great cultural importance but also have a significant economic component because cultural values of past centuries attract tourists from all over the world. The use of modern technical and scientific achievements in the field of non-destructive testing makes it possible to obtain new knowledge about cultural objects regarding their origin and dating, as well as to contribute to their better restoration and preservation. An important component of their use is additional opportunities to identify high quality fakes of original cultural objects that have historical significance. The capabilities of various non-destructive testing (NDT) methods used to examine cultural objects are characterized by their penetration depth, resolution, and sensitivity to material properties. Thus, in many cases, it is necessary to perform multi-sensor non-destructive testing and creating large data sets that require an efficient evaluation. This article considers an example of using microwave (MW) holographic sensors for the examining of an old Orthodox Russian Icon dated of the late 19th century. The paper describes the technology of microwave holography, which has recently been applied to the examination of art works. Unlike the well-studied X-ray method, MW holography makes it possible to examine objects with one-sided access. Its other advantages are the relative cheapness of the equipment and the safety of use due to the low level of radiation. The article describes a MW holograms reconstruction algorithm, as well as a method for improving the quality of obtained MW images. The data collected at MW research of the Icon are compared with the results of X-ray examination and confirmed by subsequent opening and visual examination performed by professional restorers.

In this defense I will describes three approaches to learn more about the relationship between the dynamics of black-holes and the distinctive signatures of a black hole systems: infinitesimal changes in the black hole background producing field excitations relating new fundamental black hole thermodynamic relations, mechanisms powering relativistic black hole jets and spontaneous symmetry breaking in five space-time dimensions, and physical signatures of black hole event horizons as conformal field theory duals (in both d=4,5 dimensional axisymmetric spacetimes).

Holographic displays have always shown great promise, a legitimate solution to current two dimensional stereoscopic displays. Holography is capable of demonstrating fully three-dimensional images without a loss in resolution, however, its current drawbacks such as comparatively limited field of view, limitations in hardware, with spatial light modulators mostly capable of modulating either the amplitude or phase of light, or its subpar image quality, have delayed its introduction and success in the mass market. This work focuses on the latter problem, finding novel algorithmic mechanisms for improving the image quality in replay fields. Given the nature of this issue within this field, there are numerous approaches for resolving this issue, more recently through machine learning, adopting supervised training models. This work follows a different approach. It investigates other industries, such as microscopy, astronomy, and computed tomography to draw parallels with the advances made there and adapted these implementations to computer generated holography. As a result, the Kaczmarz and later the Cimmino iterative algorithms were adapted to this problem and analysed extensively against Gerchberg-Saxton, a common algorithmic benchmark used in holographic projections. The results, in terms of image quality, are positive since in all cases these algorithms converge to a suitably low minima and display the intended replay field, whilst simultaneously outperforming Gerchberg-Saxton in several instances. Much like any other research proposal, there are always drawbacks, and trade-offs. Whilst these algorithms were shown to outperform the reference Gerchberg-Saxton in many scenarios, they are also comparatively computationally intensive and run significantly slower than the benchmark. Much of the work that followed under Cimmino was finding ways of combining these two attributes, i.e., improve the image quality as well as its speed. The Cimmino FFT algorithm was derived and equates to the more formally known Fienup algorithm. This work found a link between the Cimmino algorithm developed in the 1930s solving linear systems, to the Fienup algorithm developed in the 1970s, a well-known phase retrieval algorithm. Nevertheless, it was apparent when analysing the computational intensity of these algorithms the iterative use of discrete Fourier transforms (DFTs) and fast Fourier transforms (FFTs) requires significant processing power and is the bulk of the overall algorithmic run time. The final analysis of this thesis considers reducing this run time further by interpolating the replay field using a Hilbert curve. There is, however, another trade-off between the final image quality and the use of more DFT and FFTs against the use of interpolation, as expected. In conclusion, it can be verified that the larger the resolution of the image, the more benefit will be seen in terms of computational processing and algorithm run time, when adopting Hilbert interpolation.

Amblyopia is a significant issue for children worldwide, and current treatment methods have drawbacks that can hinder treatment effectiveness and/or patient experience. This study proposes a new treatment method using holographic diffusers while also comparing their optical characteristics to a current treatment method (Bangerter foils). Holographic diffusers were developed by optically patterning thin polymer layers on a micron scale. Two compositions of photopolymer (acrylamide and diacetone acrylamide based) are analysed herein. Characterisation shows that holographic diffusers of either composition can achieve a wide range of on-axis intensity reductions, allowing for precise and customisable treatment levels by altering recording exposure time in a low-cost and durable manner.

Metal oxide nanoparticles exhibit outstanding catalytic properties, believed to be related to the presence of oxygen vacancies at the particle’s surface. However, little quantitative information is known about concentrations of point defects inside and at surfaces of these nanoparticles, due to the challenges in achieving an atomically resolved experimental access. By employing off-axis electron holography, we demonstrate, using MgO nanoparticles as an example, a methodology that discriminates between mobile charge induced by electron beam irradiation and immobile charge associated with deep traps induced by point defects as well as distinguishes between bulk and surface point defects. Counting the immobile charge provides a quantification of the concentration of F2+ centers induced by oxygen vacancies at the MgO nanocube surfaces.

Numerous anthropogenic and natural particle contaminants exist in diverse aquatic systems, with widely unknown environmental fates. We coupled a flow tube with a digital in-line holographic microscopy (nano-DIHM) technique for aquatic matrices, for

Tomographic diffraction microscopy (TDM) is a tool of choice for high-resolution, marker-less 3D imaging of biological samples. Based on a generalization of digital holographic microscopy with full control of the sample's illumination, TDM measures, from many illumination directions, the diffracted fields in both phase and amplitude. Photon budget associated to TDM imaging is low. Therefore, TDM is not limited by phototoxicity issues. The recorded information makes it possible to reconstruct 3D refractive index distribution (with both refraction and absorption contributions) of the object under scrutiny, without any staining. In this contribution, we show an alternate use of this information. A tutorial for multimodal image reconstruction is proposed. Both intensity contrasts and phase contrasts are proposed, from the image formation model to the final reconstruction with both 2D and 3D rendering, turning TDM into a kind of 'universal' digital microscope.

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.

Nowadays, the study and optimization of volume holographic lenses (HLs) stored in low-toxicity photopolymers have a great interest. HLs are now a component of optical imaging systems that are mostly used in head-mounted displays for virtual and augmented reality or as non-image systems in light deflectors and concentrators. One of the most important parameters used when working with imaging systems is the resolution of the optical system. In this work, the similarity between the object and image of negative asymmetrical HLs stored in a low-toxicity photopolymer named Biophotopol has been evaluated theoretically and experimentally. For this purpose, the resolution of the HLs was calculated using the Convolution Theorem. A USAF 1951 test was used as an object and the impulse responses of the HLs were obtained with two different sensors: CCD and Hartmann-Shack (HS) wavefront sensor. In addition, the resolution of the HLs has been obtained by two different methods: one using the Convolution Theorem, using both the CCD and the HS wavefront sensor, and the other by forming the USAF test image on the CCD sensor. Finally, a theoretical study of object-image similarity was carried out using the MSE (mean squared error) metric to evaluate the quantitative experimental results. This research was funded by Universidad de Alicante (UAFPU20-23); Generalitat Valenciana (CIDEXG/2022/60, IDIFEDER/2021/014, PROMETEO/2021/006); Ministerio de Ciencia e Innovación (PID2019-106601RB-I00, PID2021-123124OB-I00).

In the last few years, the interest in storing volume holograms in photopolymers has increased enormously due to their applications in industry, the medical field, security, or renewal energy among others. The production of environmentally compatible photopolymers is one of the main focuses of Holography research. In this work, we have studied how to increase the diffraction efficiency of reflection holograms stored in a low-toxicity PVA-based photopolymer called Biophotopol. The holographic material has been doped with different types of nanoparticles (NPs) to achieve an increase in the refractive index modulation during the recording stage. Metallic NPs, obtained by physical and electrochemical methods have been used. The results obtained with all of them have been compared as a function of the concentration used, the size of the NPs, and the stabilization method used for their synthesis. A considerable increase in diffraction efficiency has been achieved by using NPs in the low-toxicity material. By using high refractive index NPs, the average refractive index of the holographic material increases and consequently the diffraction efficiency. This research was funded by Generalitat Valenciana, Spain, under projects PROMETEO/2021/006, IDIFEDER/2021/014 (co-funded by European Union through the FEDER Program) and CIDEXG/2022/60; Universidad de Alicante, Spain, under project UAFPU20-23 and Ministerio de Ciencia e Innovación, Spain, under projects PID2019-106601RB-I00 and PID2021-123124OB-I00.

Photopolymers are designed and engineered with versatile applications including optics and photonics. Holography is one of the classical porpoises that use photopolymers as holographic recording materials. The success of these materials can be seen in the market with the photopolymer fabricated by Covestro. Some of these holographic applications require a long-time life of the holograms recorded in photopolymers. Nevertheless, initial tests of Covestro holograms show significant degradation after less than one year of exposure even after sealing and degradation occurs under solar light exposition. In this sense, it is important to perform deeper studies of the different possibilities for hologram conservation. Usually, the first step after recording is the material cure, with UV or visible light, to eliminate the residual dye and monomer. With this process high efficiency holograms can also be obtained. Afterwards, an index matching technique can be used to cover the material with a glass or it is possible the application of aerosol sealant. In this paper we analyze the introduction of holograms between two glasses linked by pressure, using Bayfol HX 200 from Covestro as the recording material. In order to characterize the process, four different spatial frequencies were tested, which were stored either by transmission or reflection schemes. The data of the reconstruction step has been measured before and after the encapsulation. In addition, multiple holograms have been superposed in the same glass, where we have found that shrinkage is more significant. The work was supported by the “Generalitat Valenciana” (Spain) project PROMETEO/2021/006 and by the ‘‘Universidad de Alicante’’ (UATALENTO18-10; ACIE-20-10). Generalitat Valenciana (Spain) (IDIFEDER/2021/014, cofunded by European Union through the FEDER Programme and “Ministerio de Ciencia e Innovación” of Spain (project PID2021-123124OB-I00).

To identify sound source locations by using Fourier-based Near-field Acoustical Holography (NAH), a large number of microphone measurements is generally required to span the source region and ensure a sufficiently high spatial sampling rate. As a result, such measurements are costly, a fact which has discouraged the industrial application of NAH to identify sound source locations. However, recently, compressive sensing approaches have made it feasible to identify concentrated sound sources with a limited number of microphone measurements. In the present work, sound radiation from the front face of a diesel engine was measured by using one set of measurements from a 35-channel combo-array. The locations of significant noise sources were then identified by using three compressive sensing algorithms: Wideband Acoustical Holography (WBH), l1-norm minimization, and a hybrid approach which combined WBH and l1-norm minimization. The latter approach takes advantage of the l1’ norm’s ability to locate spatially distinct sources, and WBH’s ability to suppress “ghost” sources. It was found that the hybrid algorithm can localize and visualize the major noise sources over a broad range of frequencies, even though using a relatively small number of microphones. Finally, comments are made regarding sound field reconstruction differences between the algorithms.

Holography is an advanced three-dimensional (3D) imaging and visualisation technology capable of reconstructing realistic 3D scenes. Despite decades of concentrated effort, holographic 3D displays are still struggling to meet the demands required for a consumer-ready solution. This thesis addresses technical challenges in the practical implementation and focuses specifically on potential image quality improvements based on algorithmic development. The thesis builds a holographic display system prototype and reconstructs established 3D scenes and real-world scenes using commercially available RGB-D cameras. By closely examining the reconstructed images, experimental reconstruction issues are evaluated. Given that image quality degradation is one of the significant issues in holographic displays, the gradient descent method is introduced to phase-only CGH optimisation. Contemporary image quality metrics (IQMs) considering human visual systems are employed as loss functions to improve the reconstructed image quality. Extensive objective and subjective assessment of experimentally reconstructed images reveal that the perceived quality improves considerably should the appropriate IQM loss be selected. Finally, the gradient descent method is extended to 3D hologram generation. While previous work optimises 3D CGH generation primarily on the in-focus region, this research further combines the method with an incoherent imaging module and a reformulated loss function to improve the defocus effect without sacrificing in-focus image quality. The experimentally acquired result demonstrates its effectiveness in reconstructing realistic 3D images beyond the capabilities of existing 3D hologram generation algorithms.

Holography uses the interference of light waves to store information about an object, which can then be seen from different angles to create a partial 3D view. A simple experiment can be done using a laser diode, photographic plate, and a set of dice to create a holographic image. The holographic film is thin and can only hold a single image. Reflection holography can create a 3D diffraction pattern and allows more information to be packed into a single medium. Computer generated holograms can be designed to create holograms without a real object to be used in augmented reality. High resolution holograms can be created by nanofabrication. Metasurfaces are sub-wavelength patterns generated by computers on a surface to create vortex beams for optical communication and other applications.

International audience; Perpendicular shape anisotropy (PSA) offers a practical solution to downscale spin-transfer torque magnetoresistive random-access memory (STT-MRAM) beyond the sub-20 nm technology node while retaining thermal stability. However, our understanding of the thermomagnetic behavior of PSA-STT-MRAM is often indirect, relying on magnetoresistance measurements and micromagnetic modeling. Here, the magnetism of a NiFe PSA-STT-MRAM nanopillar is investigated using off-axis electron holography, providing spatially resolved magnetic information as a function of temperature. Magnetic induction maps reveal the micromagnetic configuration of the NiFe storage layer (∼60 nm high, ≤20 nm diameter), confirming the PSA induced by its 3:1 aspect ratio. In situ heating demonstrates that the PSA of the storage layer is maintained up to at least 250 °C, and direct quantitative measurements reveal a moderate decrease of magnetic induction. Hence, this study shows explicitly that PSA provides significant stability in STT-MRAM applications that require reliable performance over a range of operating temperatures.

Light detection and ranging (LIDAR) systems are finding their way into an increasing number of applications including autonomous vehicles. Image sensors based on single-photon avalanche diode (SPAD) arrays have demonstrated great promise for LIDAR, typically using flood illumination or raster-scanning of a small spot. Holographic illumination, based on phase-only liquid crystal on silicon (LCoS) spatial light modulators, has been successfully applied to display systems such as automotive head up displays (HUDs). It holds great promise as the method of illumination for a LIDAR system. We present a novel solid-state LIDAR architecture using holographic projection and single-photon detection. We report a simple experiment that demonstrates proof of concept. The results of the experiment show that the novel architecture can improve the depth accuracy of 3D imaging compared to conventional LIDAR systems. We also indicate several key performance advantages of the novel architecture that will increase as the system scales to higher performance.

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.

Y and Zr Kα X-ray fluorescence holography measurements were carried out on a single crystal of yttria-stabilized zirconia with 13 mol% of yttria at room temperature to investigate the local structures around the impurity Y and host Zr atoms. Around the central Y atom, the images of the surrounding Zr/Y atoms are seen as a face-centered-cubic (fcc) sub-lattice. Thus, the impurity Y atoms are sure to be replaced with the Zr atoms as expected earlier. In addition, strong images are also observed, by which some of the Y atoms are located at the interstitial positions at the center of the fcc lattice. The atomic images around the central Zr atom are very weak, indicating large lattice distortions around the Zr atom. Some images outside of the ideal fcc lattice indicate that the local structures around the Zr atoms are similar to the original pure monoclinic ZrO2, and some of them would be rotated due probably to the interstitial doping of the impurity Y atoms.

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.

The orbital angular momentum (OAM) holography has been developed and experimentally demonstrated the capability of holographic multiplexation and high-security encryption. However, the helical phase of an OAM mode can only be encoded into one hologram associated with a target image, and this severely limits the information capacity in practical applications. The modulated orbital angular momentum (MOAM) holography is proposed by imposing multiple modulation phase modes onto one OAM mode. Three essential properties, including the MOAM-preservation, MOAM-selectivity and MOAM-multiplexation are investigated. This method can significantly enhance the holographic information capacity and it has broad prospects for optical encryption and beam manipulations.

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.

In this thesis, we study one-dimensional, matrix-valued quantum mechanical models. These models, exhibit numerous characteristics and can be used to study various problems. One among these problems is their gravitational nature, giving some hints about a quantum theory of gravity. The latter emanates from string theory since string theory already contains the matrix models. Therefore, by studying these models, we can understand aspects of a quantum gravitational theory, unraveling this way, some mechanisms present only in quantum gravity. To attack this problem and due to the difficulty of getting analytic solutions because of the matrix character of the model, we deploy some numerical approaches based on Monte Carlo simulation. In this way, we can understand gravitational features non-perturbatively, equipping us with a powerful tool to explore quantum gravity in regimes not studied in the past., In dieser Arbeit untersuchen wir eindimensionale, matrixwertige quantenmechanische Modelle. Diese Modelle zeigen zahlreiche Eigenschaften und können zur Untersuchung verschiedener Probleme verwendet werden. Eines dieser Probleme ist ihre gravitative Natur, die einige Hinweise auf eine Quantentheorie der Gravitation gibt. Letztere leitet sich von der Stringtheorie ab, da die Matrixmodelle bereits in der Stringtheorie enthalten sind. Daher können wir durch die Untersuchung dieser Modelle Aspekte einer quantenmechanischen Gravitationstheorie verstehen und auf diese Weise einige Mechanismen aufdecken, die nur in der Quantengravitation vorhanden sind. Um dieses Problem anzugehen und aufgrund der Schwierigkeit, analytische Lösungen aufgrund des Matrixcharakters des Modells zu erhalten, setzen wir einige numerische Ansätze auf Basis von Monte-Carlo-Simulationen ein. Auf diese Weise können wir gravitative Merkmale nicht-perturbativ verstehen und uns mit einem leistungsstarken Werkzeug ausstatten, um die Quantengravitation in Regimen zu erkunden, die in der Vergangenheit nicht untersucht wurden.

We discuss interrelations between several ideas in quantum gravity. One is the Swampland program, which states that a low-energy effective field theory should satisfy non-trivial constraints to have an ultraviolet (UV) completion in quantum gravity. Another is the concept of ensemble averaging in holography, where a coarse-grained description is obtained by an integral over a moduli space. To examine the relation between the two, we study ensemble averages of generalized Narain-type theories associated with a general even quadratic form and their holographic duals. We establish the emergence of global symmetries and discuss their consistency with the Swampland conjecture forbidding exact global symmetries. Out of all the zero-form symmetries, the quantum symmetries in the bulk are truly emergent, while classical symmetries are identified as vestiges of T-duality of the Narain-type theories. The latter mechanism can be formulated very generally as a ``folding'' of T-duality orbits via the Siegel-Weil Theorem. We also discuss the interrelations between the Swampland distance conjecture, on one hand, and ensemble averaging and spectral decompositions, on the other. The spectral decomposition also illustrates how ensemble averaging sits within the low-energy limit of certain string compactifications. Our analysis suggests fascinating links between the Swampland, the Landscape, and ensemble averaging., Comment: 6 pages

Light-sheet microscopy is a powerful method for imaging small translucent samples in vivo, owing to its unique combination of fast imaging speeds, large field of view, and low phototoxicity. This chapter briefly reviews state-of-the-art technology for variations of light-sheet microscopy. We review recent examples of optogenetics in combination with light-sheet microscopy and discuss some current bottlenecks and horizons of light sheet in all-optical physiology. We describe how 3-dimensional optogenetics can be added to an home-built light-sheet microscope, including technical notes about choices in microscope configuration to consider depending on the time and length scales of interest.

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.

In four-dimensional $\mathcal{N}=4$ super Yang-Mills theory with gauge group $SU(N)$, we present a closed-form solution for a family of integrated four-point functions involving stress tensor multiplet composites of arbitrary R-charge. These integrated correlators are shown to be equivalent to a one-dimensional semi-infinite lattice of harmonic oscillators with nearest-neighbor interactions, evolving over the fundamental domain of $SL(2,\mathbb{Z})$. The solution, exceptionally simple in an $SL(2,\mathbb{Z})$-invariant eigenbasis, is exact in the R-charge $p$, rank $N$, and complexified gauge coupling $\tau$. This permits a systematic and non-perturbative large charge expansion for any $N$ and $\tau$. Especially novel is a double-scaled "gravity regime" in which $p \sim N^2 \gg 1$, holographically dual to a large charge regime of semiclassical type IIB string theory in AdS$_5\, \times$ S$^5$. Our results in this limit provide a holographic computation of integrated semiclassical string amplitudes at arbitrary string coupling, including an emergent string scale with a large charge dressing factor. We compare to extremal correlators in superconformal QCD, for which we predict new genus expansions at large charge scaling with $N$., Comment: 31 pages + appendices

Robust open-source digital lensless holographic microscope, functionalized for the label-free analysis of blood smear samples.

We improve the holographic description of isospin-asymmetric baryonic matter within the Witten-Sakai-Sugimoto model by accounting for a realistic pion mass, computing the pion condensate dynamically, and including rho meson condensation by allowing the gauge field in the bulk to be anisotropic. This description takes into account the coexistence of baryonic matter with pion and rho meson condensates. Our main result is the zero-temperature phase diagram in the plane of baryon and isospin chemical potentials. We find that the effective pion mass in the baryonic medium increases with baryon density and that, as a consequence, there is no pion condensation in neutron-star matter. Our improved description also predicts that baryons are disfavored at low baryon chemical potentials even for arbitrarily large isospin chemical potential. Instead, rho meson condensation sets in on top of the pion condensate at an isospin chemical potential of about $9.4\, m_\pi$. We further observe a highly non-monotonic phase boundary regarding the disappearance of pion condensation., Comment: 31 pages, 7 figures, v2: new ansatz for the bulk gauge field, eliminating an unjustified assumption in v1; as a consequence, numerous modifications in text, equations, and plots, with main conclusions unchanged

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.

We explore the holographic duality between string theory in backgrounds that interpolate between asymptotically linear dilaton spacetime in the UV and $AdS_3$ in the IR, and single-trace $T\bar T$ deformed CFT. In particular, we explain how the deformation of states in the boundary theory is reflected in the bulk geometry, and show that the coupling above which the deformed energy of the $SL(2,\mathbb{R})$ invariant ground state of the IR CFT becomes complex is a maximal coupling., Comment: 17 pages

Driven quantum systems exhibit a large variety of interesting and sometimes exotic phenomena. Of particular interest are driven conformal field theories (CFTs) which describe quantum many-body systems at criticality. In this paper, we develop both a spacetime and a quantum information geometry perspective on driven 2d CFTs. We show that for a large class of driving protocols the theories admit an alternative but equivalent formulation in terms of a CFT defined on a spacetime with a time-dependent metric. We prove this equivalence both in the operator formulation as well as in the path integral description of the theory. A complementary quantum information geometric perspective for driven 2d CFTs employs the so-called Bogoliubov-Kubo-Mori (BKM) metric, which is the counterpart of the Fisher metric of classical information theory, and which is obtained from a perturbative expansion of relative entropy. We compute the BKM metric for the universal sector of Virasoro excitations of a thermal state, which captures a large class of driving protocols, and find it to be a useful tool to classify and characterize different types of driving. For M\"obius driving by the SL(2,R) subgroup, the BKM metric becomes the hyperbolic metric on the unit disk. We show how the non-trivial dynamics of Floquet driven CFTs is encoded in the BKM geometry via M\"obius transformations. This allows us to identify ergodic and non-ergodic regimes in the driving. We also explain how holographic driven CFTs are dual to driven BTZ black holes with evolving horizons. The deformation of the black hole horizon towards and away from the asymptotic boundary provides a holographic understanding of heating and cooling in Floquet CFTs., Comment: 82 pages including references, 14 figures

An analog holographic wavefront sensor (AHWFS), for measurement of low and high order (defocus and spherical aberration) aberration modes has been developed as volume phase holograms in a photopolymer recording medium. This is the first time that high order aberrations such as spherical aberration can be sensed using a volume hologram in a photosensitive medium. Both defocus and spherical aberration were recorded in a multi-mode version of this AHWFS. Refractive elements were used to generate a maximum and minimum phase delay of each aberration which were multiplexed as a set of volume phase holograms in an acrylamide based-photopolymer layer. The single-mode sensors showed a high degree of accuracy in determining various magnitudes of defocus and spherical aberration generated refractively. The multi-mode sensor also exhibited promising measurement characteristics and similar trends to the single-mode sensors were observed. The method of quantifying defocus was improved upon and a brief study into material shrinkage and sensor linearity is presented.

ZusammenfassungVirtuelles Netzwerken ist seit Beginn der Corona-Pandemie ein zentrales Mittel geworden, um sich zu vernetzen. Mit dem einschneidenden Ereignis von COVID-19 sind zahlreiche Alternativen zu traditionellen Netzwerkveranstaltungen wie Messen, Abendessen etc. entstanden. Hierbei traten jedoch auch viele Hürden auf, etwa die fehlende Menschlichkeit oder das zweidimensionale Erscheinungsbild im digitalen Raum. Ein Ansatz diese Herausforderungen zu überwinden, liegt in der Kombination von erweiterter Realität (engl. augmented reality (AR)) und Holografie. Um die technische Machbarkeit dieses Ansatzes zu überprüfen, haben wir mit AR-Experten und Kunden gesprochen und die Faktoren für und gegen die Nutzung von AR und Holografie zum Netzwerken diskutiert. Unsere Ergebnisse zeigen, dass die Experten und Kunden hohes Potenzial in der Kombination sehen. Doch mangelt es momentan noch an technologischen Lösungen, um dies breitenwirksam einsetzen zu können. Die Experten und Kunden sind sich resümierend einig, dass es, basierend auf den aktuellen technischen Entwicklungen im Bereich AR und Holografie, in naher Zukunft dafür Lösungen geben wird und die Kombination von AR und Holografie dann eine gute Alternative zum Netzwerken darstellen kann. Daraus folgern wir, dass ortsunabhängiges Netzwerken mit AR und Holografie eine Welt zum Wohlfühlen für die Nutzenden schafft und einen klaren Mehrwert darstellt.

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.