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In this work, we implemented an off-axis digital holographic microscopy (DHM) setup to study the behavior of liquid drops on nanostructured porous silicon (PS) membranes. When a liquid comes into contact with the PS structure, capillary action and surface tension give rise to imbibition of the liquid into the intricate volume of the pores. At the same time, the vapor field developed around the drop enhances liquid condensation and evaporation into and from the pores. The complex interplay between these phenomena (capillary driven internal flows, condensation, and evaporation) is not yet fully understood but the methods we propose can provide new insights. We demonstrate how DHM allows determining the filling fraction of the porous membrane around drying drops of water and isobutyl alcohol. The phase information obtained from registered holograms provides quantitative information that permits to reconstruct the filling fraction along the porous membrane and its evolution during the drying process. Additionally, relevant parameters such as speed and contact angle during retraction of the drops can be measured. These methods can be further extended to other porous materials, such as porous alumina, micro- and macro-PS, to develop better fluid-dynamic models for describing fluid behavior in highly confined structures. [ABSTRACT FROM AUTHOR]

Mode coupling and conversion between longitudinal and transverse modes are ubiquitous and universal in elastic waves, presenting a challenge in realistic applications such as nondestructive evaluation and geological exploration, where independent and separate manipulation of each mode is demanded. In this article, we propose a design of elastic metalens that can realize a high-efficiency focusing for the longitudinal wave and a V-shaped converging pattern for the transverse wave at the same time. The metalens is constructed from a metagrating, where each meta-atom has a simple configuration and renders high diffraction efficiency even for large steering angles, enabled by concurrent utilization of grating diffraction theory and advanced optimization algorithms. Interestingly, an arbitrary energy splitting ratio between the reflected longitudinal and transverse waves can be obtained by precisely controlling the coupling strength and conversion efficiency between them, providing improved flexibility and adaptability to various application environments. Two illustrative examples with a sharp focusing effect and tailored conversion efficiency are explicitly demonstrated, with a 50/50 energy splitting ratio between the longitudinal and transverse waves in the first case, and a 70/30 ratio in the second one. [ABSTRACT FROM AUTHOR]

Liquid crystal polarization gratings liquid crystal Pancharatnam‐Berry phase optical element (LCPGs) are a superior alternative to traditional diffraction gratings due to their high diffraction efficiency, strong polarization sensitivity, and versatile tunability. This paper introduces an electrically switchable liquid crystal polarization grating based on cholesteric liquid crystals (CLCs). The LCPG is designed to operate in reflective (R‐mode) and transmissive (T‐mode) states. It utilizes the standing helical (SH) configuration of CLCs for reflective functionality and transitions to a lying helical (LH) configuration for transmissive operations. This dual‐mode capability is achieved through a unique application of electric fields, which reorient the liquid crystal helix axis according to the desired optical function. The performance of the LCPG in both R‐mode and T‐mode is evaluated by applying different frequencies and voltages to dynamically switch between the helical states. The manufacturing process is simple, and the device performs robustly. This suggests that the technology could be useful for developing optical systems that require dynamic control over light modulation. [ABSTRACT FROM AUTHOR]

Holographic optical elements (HOEs) based on polymer composites have become a research hot spot in recent years for augmented reality (AR) due to the significant improvement of optical performance, dynamic range, ease of processing and high yield rate. Nevertheless, it remains a formidable challenge to obtain a large field of view (FOV) and brightness due to the limited refractive index modulation. Herein, we report an effective method to tackle the challenge by doping an epoxy liquid crystal termed E6M, which enables a large refractive index modulation of 0.050 @ 633 nm and low haze of 5.0% at a doping concentration of 5 wt%. This achievement may be ascribed to the improved molecular ordering of liquid crystals within the holographic polymer composites. The high refractive index modulation can endow transmission-type holographic polymer composites with a high diffraction efficiency of 96.2% at a small thickness of 5 µm, which would promise the design of thin and lightweight AR devices. [ABSTRACT FROM AUTHOR]

This paper presents the design of a low-profile circularly polarized dual-beam holographic antenna. Firstly, by employing a novel outer square inner circular (OSIC) structure as the basic unit of the hologram pattern, better performance is achieved for lowprofile dielectric substrate holographic antennas. Secondly, a method of four-zone phase co-modulation is used to derive the impedance modulation formula of the hologram pattern. This formula was employed to model and generate a circularly polarized dual-beam holographic antenna, and the feasibility of theoretical analysis is verified through simulation and measurement. The antenna operates within the frequency range of 10.23 GHz to 16.59 GHz, with maximum gains of 16 dBi and 15.8 dBi for dual beams, respectively. The results indicate that this design method can realize circularly polarized dual-beam holographic antennas and provide some reference for satellite communication applications. [ABSTRACT FROM AUTHOR]

Microwave holographic measurement technology is a common method used in antenna measurement. This method has high measurement efficiency and high precision. To evaluate and enhance the antenna's performance, it is crucial to precisely determine the surface deformation. In this paper, the effects of feed offset error and scanning error on the antenna microwave holographic measurement results are investigated, and corresponding error compensation methods are proposed. The relationship between the influence of the error sources on the antenna gain loss and surface deformation accuracy is established. The reasons for holographic measurement errors, their characteristics, and their specific impact on system performance can be better understood. In order to improve the accuracy of the measurement, the compensation methods for the different measurement errors are given. They can provide the theoretical basis for maintaining and enhancing the performance of antenna system. [ABSTRACT FROM AUTHOR]

We clarified that a ferroelectric liquid crystal (FLC) has high resolution display capability as small as 1 × 1 μm pixel pitch using an FLC pixel array with a two‐layer electrode, which has a 1 × 1‐μm‐checkered apertured electrode and a plane electrode separated by an insulation layer. By applying +2 V to the apertured electrode and −10 V to the plane electrode in the two‐layer electrode and 0 V to the transparent common electrode, a checkered pattern was clearly observed, which indicates the successful individual pixel driving with a pixel pitch of 1 × 1 μm. When fabricating 1 × 2‐μm‐pitch rectangular FLC pixels, we elucidated that the liquid crystal alignment direction should be along the shorter side of the pixels to avoid asymmetric transmittance distribution in each pixel. Moreover, we successfully reconstructed a 3D holographic image using 10 × 10 k FLC pixel array with a pitch of 1 × 1 μm driven by the two‐layer electrode with hologram‐patterned apertures. We showed that FLC is a strong candidate material for realizing spatial light modulator with extremely small pixel pitches, which is essential for holographic displays with wide‐viewing‐zone angles. [ABSTRACT FROM AUTHOR]

Fast‐switching high‐efficiency liquid crystal grating is a key component in holographic true‐3D display systems. In this paper, we present our research and development of a 10.7" liquid crystal grating with 2‐3 millisecond switching time, close‐to‐ideal deflection efficiency, and >100 polarization contrast. The high performance is achieved by optimizing the design and process of the liquid crystal grating panel as well as the optical module stack. Several key design principles are analyzed and verified. Based on the developed liquid crystal grating, a 10.4" full‐color naked‐eye holographic 3D display prototype is successfully realized. [ABSTRACT FROM AUTHOR]

We have developed a reflective polarization volume grating using liquid crystal polymer for SWIR with high efficiency and a large diffraction angle. By using this grating and a lightguide system, we demonstrated a sensor system that can capture identical images simultaneously in both visible and SWIR light. [ABSTRACT FROM AUTHOR]

Metasurface-based holograms, or metaholograms, offer unique advantages including enhanced imaging quality, expanded field of view, compact system size, and broad operational bandwidth. Multi-channel metaholograms, capable of switching between multiple projected images based on the properties of illuminating light such as state of polarization and angle of incidence, have emerged as a promising solution for realizing switchable and dynamic holographic displays. Yet, existing designs typically grapple with challenges such as limited multiplexing channels and unwanted crosstalk, which severely constrain their practical use. Here, we present a new type of waveguide-based multi-channel metaholograms, which support six independent and fully crosstalk-free holographic display channels, simultaneously multiplexed by the spin and angle of guided incident light within the glass waveguide. We employ a k-space translation strategy that allows each of the six distinct target images to be selectively translated from evanescent-wave region to the center of propagation-wave region and projected into free space without crosstalk, when the metahologram is under illumination of a guided light with specific spin and azimuthal angle. In addition, by tailoring the encoded target images, we implement a three-channel polarization-independent metahologram and a two-channel full-color (RGB) metahologram. Moreover, the number of multiplexing channels can be further increased by expanding the k-space's central-period region or combing the k-space translation strategy with other multiplexing techniques such as orbital angular momentum multiplexing. Our work provides a novel approach towards realization of high-performance and compact holographic optical elements with substantial information capacity, opening avenues for applications in AR/VR displays, image encryption, and information storage. [ABSTRACT FROM AUTHOR]

Five different foam concretes were synthesized and examined. A new hybrid optical sensor, called combined digital holographic microscopy (CDHM), was proposed by combining microscopic fringe projection profilometry and lateral shearing digital holographic microscopy to detect the pore radii of produced foamed concretes. It was applied in addition to SEM and has not been applied to foam concretes before. Thanks to the proposed method, it was revealed that the measured CDHM radii contained a relative error of less than 6% compared to the SEM radii. The pore radii increased as the % of foaming agent used in the samples increased. Accordingly, the sample densities decreased and thermal insulation properties enhanced. Two-layer quantum chemical calculations performed at the ONIOM (M06-2X/6-31+G(d,p):UFF) theoretical level showed that thermodynamic stability of foam concretes increased as the % of foaming agent used, or more precisely, the pore radius, increased. The CDHM method provides results close to SEM and has superior features such as being more cost-effective, cleaner and faster. For this reason, it is thought that the proposed method will lead to future studies in terms of measuring pore radii as an alternative to SEM. The combined digital holographic microscopy (CDHM) method is proposed as an alternative to SEM with a relative error of less than 6% in determining the pore radius of foam concretes. [ABSTRACT FROM AUTHOR]

Liquid crystalline (LC) poly(methacrylates) with azobenzene moieties in their side chains have been synthesized and their chemical structure has been confirmed with nuclear magnetic resonance spectroscopy and gel permeation chromatography. Azobenzene moieties are linked to polymer backbone via an alkyl spacer with length from 2 to 10 methylene units. Photooptical processes in thin amorphized polymer films are examined through measurements of optical anisotropy and holographic grating recording. Birefringence values induced with a linearly polarized green (532 nm) laser beam has strongly depended from the spacer length. Irradiation with two circularly polarized green laser beams leads to the formation of polarization and surface relief gratings, which have been visualized with polarized optical and atomic force microscopy, respectively. Diffraction efficiency of the recorded gratings is in correlation with the spacer length, namely, the shorter the spacer, the higher diffraction efficiency can be achieved. For polymers with short spacers polarization gratings can be easily erased by circularly polarized light, but only partial erasing of surface relief gratings is observed. The results presented offer the possibility of tailoring the chemical structure of azobenzene‐containing polymers for designing high‐efficiency media for the holographic recording. [ABSTRACT FROM AUTHOR]

Hierarchical micro/nanostructures have garnered considerable attention for their capabilities in light modulation, but the flexible fabrication of designed optical functional structures at both micro and nano scales remains challenging. Here, a polarization‐modulated patterned laser ablation method complemented by flowing liquid is proposed to fabricate hierarchical microgrooves featuring tunable cross‐sections and engraved surface nanostructures with controllable periods and orientations. The liquid‐assisted ablation counters the shielding effect of ablation debris through laser‐induced microjets, ensuring accurate control of the microgroove's shape by modulating the laser pattern in the focal plane. Simultaneously, the absence of debris also permits the consistent formation of laser‐induced periodic surface structures (LIPSS) across the microgrooves. The LIPSS's period and orientation can be finely adjusted by manipulating the pulse energy and polarization within the patterned laser spot, facilitating the adaptable creation of hierarchical micro/nanostructures for optical application needs. As a demonstration, blazed gratings featuring orientation‐customized LIPSS are fabricated, which exhibit polarization‐dependent diffraction efficiency. The laser fabrication technique offers a highly versatile solution for sculpturing shape‐controllable hierarchical gratings on hard‐to‐machine materials, paving the way for the swift production of customized optical elements. [ABSTRACT FROM AUTHOR]

Holographic Optical Elements (HOEs) employ refractive index (RI) modulation to manipulate light, establishing their widespread application in augmented and virtual reality technologies. Despite significant strides in HOEs' fabrication, a comprehensive 3D examination and measurement of these elements remain largely unexplored. This study targets this void by conducting an in‐depth exploration of the 3D RI distributions of volume holographic gratings (VHGs), a quintessential representative of HOEs. Direct tomographic measurements of the 3D RI distributions within millimeter‐scale VHGs are performed at a spatial resolution of 156 nm × 156 nm × 1.2 µm and an RI precision of 2×10−4. This level of precision facilitates a systematic high‐resolution characterization of VHGs. The findings present a substantial evolution from traditional measurement techniques and promise to considerably advance the evaluation of intricate HOE structures and refine the corresponding fabrication processes. [ABSTRACT FROM AUTHOR]

As process nodes of advanced integrated circuits continue to decrease below 10 nm, the requirement for overlay accuracy is becoming stricter. The alignment sensor measures the position of the alignment mark relative to the wafer; thus, sub-nanometer alignment position accuracy is vital. The Phase Grating Alignment (PGA) method is widely used due to its high precision and stability. However, the alignment error caused by the mark asymmetry is the key obstacle preventing PGA technology from achieving sub-nanometer alignment accuracy. This error can be corrected using many methods, such as process verification and multi-channel weighted methods based on multi-diffraction, multi-wavelength and multi-polarization state alignment sensors. However, the mark asymmetry is unpredictable, complex and difficult to obtain in advance. In this case, the fixed-weight method cannot effectively reduce the alignment error. Therefore, an adaptive weighted method based on the error distribution characteristic of a multi-channel is proposed. Firstly, the simulation result proves that the error distribution characteristic of the multi-alignment result has a strong correlation with the mark asymmetry. Secondly, a concrete method of constructing weight values based on error distribution is described. We assume that the relationship between the weight value of each channel and the deviations of all channels' results is second-order linear. Finally, without other prior process correction in the simulation experiment, the residual error's Root Mean Square (RMS) of fixed weighted method is 14.0 nm, while the RMS of the adaptive weighted method is 0.01 nm, when dealing with five typical types of mark asymmetry. The adaptive weighted method exhibits a more stable error correction effect under unpredictable and complicated mark asymmetry. [ABSTRACT FROM AUTHOR]

Herein, it is demonstrated that ultrashort spatially structured beams can sculpt a sample of gas‐phase molecules like a 4D material to produce a spatial pattern of aligned molecules whose shape and temporal evolution allow to restore the spatial light information on a time‐delayed reading pulse. To do so, the spatial phase and amplitude information of ultrashort light beams are encoded into rotational coherences of molecules by exploiting the interplay between spin angular momentum and orbital angular momentum. The field‐free molecular alignment resulting from the interaction leads to an inhomogeneous spatial structuring of the sample allowing to transfer the encoded information into a time‐delayed probe beam. The demonstration is conducted in CO2$\left(\text{CO}\right)_{2}$ molecules. Besides applications in terms of THz bandwidth buffer memory, the strategy features interesting prospects for establishing versatile optical processing of orbital angular momentum (OAM) fields, for studying various molecular processes, or for designing new photonic devices enabling to impart superpositions of OAM modes to light beams. [ABSTRACT FROM AUTHOR]

Recently, the community has seen a rise in interest and development regarding holographic antennas. The planar hologram is made of subwavelength metal patches printed on a grounded dielectric board, constituting flat metasurfaces. When a known reference wave is launched, the hologram produces a pencil beam towards a prescribed direction. Most earlier works on such antennas have considered only a single beam. For the few later ones that studied multiple beams, they were achieved either by having each beam taken care of by a distinct frequency or by partitioning the hologram, thereby depriving each beam of the directivity it could have had it not shared the holographic aperture with other beams. There have been recent studies related to the use of tensor surface impedance concepts for the synthesis of holograms which have attained control over the polarizations and intensities of the beams. However, this approach is complicated, tedious, and time-consuming. In this paper, we present a method for designing a planar holographic leaky-wave multi-beam metasurface antenna, of which each simultaneous beam radiating at the same frequency towards any designated direction has a tailorable amplitude, phase, and polarization, all without hologram partitioning. Most importantly, this antenna is exempted from the need for the cumbersome technique of tensor impedance. Such features of beam configurability are useful in selective multiple-target applications that require differential gain and polarization control among the various beams. Only a single source is needed, which is another benefit. In addition, effective methods to mitigate sidelobes are also proposed here. Designs by simulations according to the method are herein validated with measurements performed on fabricated prototypes. [ABSTRACT FROM AUTHOR]

Underwater spectral detection plays an important role in the study of the underwater environment, ecology, oceanography, and environmental monitoring. A kind of underwater spectral radiometer that can observe the distribution of underwater spectral radiation bidirectionally has been developed. The flat-field concave holographic grating is used as the only optical component, the optical design parameters are optimized, and the system is miniaturized. The mechanism of stray light generation in the spectrometer is studied, and a method of suppressing stray light is proposed and simulated. The level of stray light in the system is suppressed to the order of 10−4, the signal-to-noise ratio of the system is improved, and the ability to detect weak light is enhanced. The wavelength calibration experiment was completed, and the experimental results show that the wavelength resolution of the underwater spectral radiometer is better than 3 nm. Finally, the quantitative relationship between spectral irradiance and digital output is obtained through radiation in the calibration of the system. [ABSTRACT FROM AUTHOR]

Recently, there has been great interest in the phenomenon of severe violation of the Wiedemann–Franz law in graphene Dirac fluids around 75 K, due to the strong coupling relativistic plasma near the neutral point, where traditional perturbation theory fails. To explain this phenomenon, this article proposes a holographic dual two-current axion coupling model, describing the interaction between electrons and holes in graphene near the charge neutrality point (CNP) and revealing the related physical mechanism. The study shows that the holographic two-current model aligns with experimental results at 100 μ m - 2 , and correctly predicts conductivity as temperature increases. Additionally, the article explores the behavior of β + γ and its impact on conductivity and thermal conductivity. The results suggest a frictional effect between electrons and holes. Consequently, this study provides us with a clearer understanding of the properties of graphene Dirac fluids and further confirms the reliability of the holographic duality method. [ABSTRACT FROM AUTHOR]

We propose a simulation method for two‐dimensional (2D) crossed‐type exit pupil expansion based on polarization volume grating (PVG) applied in diffractive waveguide holographic display. The functions of turning and decoupling of the PVG are realized through two continuous Bragg regions, and the spatial director distribution of liquid crystal is combined with RCWA to model its diffractive characteristics and ray tracing simulation. [ABSTRACT FROM AUTHOR]

The ability of liquid crystal to self‐organize into complicated structures can be harnessed in applications such as thin film optical devices, diffraction gratings or smart windows. In this work we focus on liquid crystal layers in contact with one or two substrates that have been patterned by photoalignment. This leads to geometric phase gratings, in which the phase of transmitted or reflected light depends on the location on the substrate. It has been shown that geometric phase gratings with uniform rotation can achieve very high diffraction efficiencies (>90%) for incident light that is circularly polarized. [ABSTRACT FROM AUTHOR]

Augmented reality (AR) displays are gaining attention as next‐ generation intelligent display technologies. To further address the demand for a wide field of view (FOV) in AR displays, gradient period polarization volume holographic gratings (PVGs) are proposed as coupling devices for diffractive waveguides. Here, a novel modeling method for gradient period PVGs are proposed by incorporating grating stacking and scattering analysis utilizing rigorous coupled‐wave analysis (RCWA) theory. The diffraction efficiency and polarization response were extensively explored using this simulation model. [ABSTRACT FROM AUTHOR]

In this paper, we summarize the various opportunities and challenges in Photopolymer based VHG optical waveguides. By comparing with SRG, we analyzed the advantages of VHG in rainbow effect and eye glow in principle. Besides, we list the challenges faced by VHGs such as grating vector testing, shrinkage effect, light leakage, and material absorption, and give some of the solutions as well as possible solution ideas. The solution of the above challenges will provide new theoretical and technical support for the practicalization of VHG optical waveguides. [ABSTRACT FROM AUTHOR]

Retroreflective gratings serve as fundamental optical elements in nanophotonics, with polarization-independent diffraction efficiency being one of the critical parameters for assessing their performance. In the far-infrared spectral range, traditional retroreflective gratings typically refer to metal echelette gratings, but their diffraction efficiency cannot approach 100% due to metal absorption. In the visible and near-infrared spectral ranges, metal echelette gratings have gradually been replaced by all-dielectric metasurfaces because dielectric materials exhibit negligible absorption at specific wavelengths. However, there is still a lack of relevant research in the far-infrared range, mainly due to the weak control capability of the existing devices over the polarization-independent phase. Here, we propose a kind of all-dielectric retroreflective metasurface composed of asymmetric pillars and freely tunable aperiodic multilayer films. The pillar structure can achieve polarization insensitivity, and the insufficient modulation capability of the dielectric materials can be compensated for by aperiodic Ge/ZnS films. The designed metasurface achieves the diffraction efficiency by RCWA, with the maximum larger than 99% and the overall reaching 95% (9.3–9.6 µm). We have provided detailed explanations of the design methodology and fabrication process. Our work lays the groundwork for further exploration and application of far-infrared lasers. [ABSTRACT FROM AUTHOR]

Photopolymers, especially acrylate-based ones with low cost and simple preparation, are promising materials for high-efficiency holographic gratings. However, it is still challenging to achieve high-performance gratings, due to the influences of many factors. In this work, we found that the dark reaction plays a critical role. The effect of the dark reaction on the optical properties of holographic gratings was investigated. Experimental results reveal that the diffraction efficiency of the gratings can be improved by a factor of three by involving the dark reaction process, and the highest diffraction efficiency for gratings can reach 97.8% after optimization. Therefore, the dark reaction can greatly enhance the optical performance of acrylate-based holographic gratings and other optical elements, thus holding great potential for many applications. [ABSTRACT FROM AUTHOR]

Metasurface holograms offer various advantages, including wide viewing angle, small volume, and high resolution. However, full-color animation of high-resolution images has been a challenging issue. In this study, a full-color dielectric metasurface holographic movie with a resolution of 2322 × 2322 was achieved by spatiotemporally multiplexing 30 frames with blue, green, and red color channels at the wavelengths of 445 nm, 532 nm, and 633 nm at the maximum reconstruction speed of 55.9 frames per second. The high average transmittance and diffraction efficiency of 92.0 % and 72.7 %, respectively, in the visible range, were achieved by adopting polarization-independent silicon nitride waveguide meta-atoms, resulting in high color reproducibility. The superposition of three wavelengths was achieved by adjusting the resolutions and positions of target images for each wavelength while maintaining the meta-atom pitch constant. The improvement in diffraction efficiency was brought about by the optimization of etching conditions to form high-aspect vertical nanopillar structures. [ABSTRACT FROM AUTHOR]

In this paper, we have applied a holographic time-of-flight technique with a nanosecond laser pulse to perform time-resolved measurements of optically induced gratings in bent-core nematics formed by a new kind of liquid crystal (LC). The effects of the electric field, laser pulse energy, temperature, and light intensity pattern on the photocharge transport process were investigated systematically. The results indicate that some peculiar features, such as high photosensitivity, relatively large mobility, and negative conductivity anisotropy, were present in the studied soft-matter system. Furthermore, a coupling between the optically induced grating and electrically induced convection was observed, which revealed a competitive state between them via the transport process. Thus, a better understanding of the carrier transport process involving photosensitivity and response time will help to tailor LC devices toward novel optical applications. [ABSTRACT FROM AUTHOR]

Efficient and accurate phase gratings hold immense significance in the realization of large format heterodyne array receivers at terahertz frequencies. Metallic phase gratings have made substantial advancements in terms of operating wavelength and the number of diffraction beams. Like most other diffractive optical devices, metallic phase gratings are primarily optimized to operate at one specific wavelength. Metasurfaces compositing arrays of subwavelength nanostructures have been demonstrated with various optical functions, by freely modifying the polarization, phase, and amplitude of light. In this study, we present an approach to create a multi-wavelength phase grating compositing segments that incorporate multiple nanostructures. The resulting transmission phase grating not only exhibits uniform diffraction beams (2 × 2) but also achieves the same diffraction angles at both 1.31 and 2.7 THz. The measured total power efficiency of the diffraction beam pattern is 53.2% for 1.31 THz and 42.4% for 2.7 THz. These devices can be applied in terahertz astronomical observations and fluorescence microscopy applications, where multi-wavelength operation is necessary. [ABSTRACT FROM AUTHOR]

The polarization state of light waves significantly affects the quality of holographic recordings. This paper quantitatively analyzes the impact of different polarization states of signal and reference beams on the quality of holographic recordings in PQ/PMMA photopolymer systems during the holography process. By deriving the light field distribution of the interference between two light waves of different polarization states and introducing the interference fringe contrast and the modulation of the refractive index of the photopolymer, we established the relationship between the diffraction efficiency of PQ/PMMA photopolymer holographic gratings and the angle between polarization directions. Based on this relationship, simulations and experiments were conducted. The experimental results demonstrated that as the angle between the polarization directions increased, the diffraction efficiency of the material decreased, with the efficiency dropping to 24.69% of its original value when the angle increased from 0° to 50°. When the angle increased to 60°, the influence of polarization characteristics became gradually significant, and at 90°, it was entirely dominated by polarization characteristics. The photoinduced birefringence properties of the PQ/PMMA prepared in the measurement experiment were studied, and the polarization characteristics of the reconstructed light under polarization direction angles of 0°, 60°, and 90° were investigated. The results indicated that at a polarization direction angle of 60 degrees, the material exhibited a significant response to the polarization information of the signal light. Finally, holographic recordings of objects at different polarization direction angles were conducted, and the reconstructed images were used to visually reflect the impact of the polarization direction angle on the quality of holographic recordings. [ABSTRACT FROM AUTHOR]

We explore the state of matter characterized by the charged timelike vector order parameter. We employ holographic duality in order to construct such a state and study its thermoelectric transport, fermionic spectral function and the character of the Meissner effect. We uncover the unusual features of this "timelike superconductor": the absence of the gap in the fermionic spectrum and co-existence of Drude peak and supercurrent in the AC transport, which are reminiscent to those of time-reversal-odd and gapless superconductors, correspondingly. We show that this state is dynamically stable and thermodynamically at least metastable. Along the way we develop the holographic model of the charged vector field, which acquires mass due to a variant of the Stueckelberg mechanism with the adjoint Higgs field. [ABSTRACT FROM AUTHOR]

In recent years, manipulations of amplitudes and phases of circularly polarized (CP) waves using metasurfaces have attracted significant attention. However, most of the current works are limited to operating in reflection or transmission space, and the amplitude manipulations are mainly achieved through polarization conversion or resistive loss, which will inevitably lead to cross‐polarization pollution and energy waste. Here, a transmission–reflection‐integrated metasurface that can manipulate the amplitudes and phases of the CP waves simultaneously in full space, which can not only realize arbitrary amplitude allocation of transmitted and reflected CP waves but also independently manipulate their phase responses is proposed. As proofs of concept, two integrated metasurfaces are designed and demonstrated, including a CP reflectarray antenna with simultaneously low side‐lobe level and low cross‐polarization level, and a meta‐grating that can arbitrarily control the intensity of transmitted diffraction wave while focusing the reflected wave. Both simulated and measured results agree very well with the theoretical predictions, demonstrating the powerful ability of the proposed metasurface to control the CP waves in full space, which is promising to be applied in future satellite communications, photonic meta‐devices, and so on. [ABSTRACT FROM AUTHOR]

The increase in bacterial resistance to antibiotics in recent years demands innovative strategies for the detection and combating of biofilms, which are notoriously resilient. Biofilms, particularly those on contact lenses, can lead to biofilm-related infections (e.g., conjunctivitis and keratitis), posing a significant risk to patients. Non-destructive and non-contact sensing techniques are essential in addressing this threat. Digital holographic tomography emerges as a promising solution. This allows for the 3D reconstruction of the refractive index distribution in biological samples, enabling label-free visualization and the quantitative analysis of biofilms. This tool provides insight into the dynamics of biofilm formation and maturation on the surface of transparent materials. Applying digital holographic tomography for biofilm examination has the potential to advance our ability to combat the antibiotic bacterial resistance crisis. A recent study focused on characterizing biofilm formation and maturation on six soft contact lens materials (three silicone hydrogels, three hydrogels), with a particular emphasis on Staphylococcus epidermis and Pseudomonas aeruginosa, both common culprits in ocular infections. The results revealed species- and time-dependent variations in the refractive indexes and volumes of biofilms, shedding light on cell dynamics, cell death, and contact lens material-related factors. The use of digital holographic tomography enables the quantitative analysis of biofilm dynamics, providing us with a better understanding and characterization of bacterial biofilms. [ABSTRACT FROM AUTHOR]

Measurement traceability is a prerequisite for achieving accurate and reliable results as well as technical standardization. The period of Chromium (Cr) gratings fabricated by atomic lithography can be directly traced back to natural constants. Applying the Cr grating to grating interferometry can achieve nanometer measurement traceability. This research aims to analyze the diffraction efficiency characteristics of self-traceable Cr gratings to provide a theoretical basis for the fabrication and application of Cr gratings. In this regard, we establish the theoretical model of the laser beam incident angle and grating diffraction efficiency using the rigorous coupled-wave method. Then, we analyze the influence of the laser beam incident angle on grating diffraction efficiency by simulation, verify the accuracy of the theoretical model, and finally build a measurement system for grating diffraction efficiency. Through experiments, we find that the diffraction efficiency of the grating shows a rapid increase to reach a stable maximum value followed by a decrease, when a laser beam with a wavelength of 405 nm is incident on the surface of a self-traceable grating in Transverse Magnetic (TM) polarization and the incident angle changes within an effective range. The experimental results are consistent with the trend of theoretical calculation results. [ABSTRACT FROM AUTHOR]

Slanted gratings serve as a crucial component in the optical waveguide couplers utilized in augmented virtual reality (AVR) devices. The flat bottom surface of slanted gratings ensures excellent diffraction efficiency of the couplers. However, achieving a flat bottom surface during the fabrication process poses challenges. This study presents a comprehensive investigation on the process control of the bottom angle using both simulation predictions based on available process parameters and experimental methods. The results obtained from the experimental procedures clearly demonstrate that the bottom angle is significantly influenced by the angular dependence of etching yield. Various ion incident energies and Ar/CHF3 gas components were employed to modulate the angular dependence of etching yield, thereby controlling the bottom angle in the reactive ion beam etching system. The effects of the ion incident energies and the flow ratios of the Ar/CHF3 gases on the bottom angle were thoroughly investigated. The findings of this study provide valuable insights for manufacturing slanted gratings and contribute to the advancement of AVR technology. [ABSTRACT FROM AUTHOR]

Expectation values of surface operators suffer from logarithmic divergences reflecting a conformal anomaly. In a holographic setting, where surface operators can be computed by a minimal surface in AdS, the leading contribution to the anomaly comes from a divergence in the classical action (or area) of the minimal surface. We study the subleading correction to it due to quantum fluctuations of the minimal surface. In the same way that the divergence in the area does not require a global solution but only a near-boundary analysis, the same holds for the quantum corrections. We study the asymptotic form of the fluctuation determinant and show how to use the heat kernel to calculate the quantum anomaly. In the case of M2-branes describing surface operators in the N = (2 , 0) theory in 6d, our calculation of the one-loop determinant reproduces expressions for the anomaly that have been found by less direct methods. [ABSTRACT FROM AUTHOR]

Efficient fiber-to-chip couplers for multi-port access to photonic integrated circuits are paramount for a broad class of applications, ranging, e.g., from telecommunication to photonic computing and quantum technologies. Grating-based approaches are often desirable for providing out-of-plane access to the photonic circuits. However, on photonic platforms characterized by a refractive index ≃ 2 at telecom wavelength, such as silicon nitride or thin-film lithium niobate, the limited scattering strength has thus far hindered the achievement of coupling efficiencies comparable to the ones attainable in silicon photonics. Here we present a flexible strategy for the realization of highly efficient grating couplers on such low-index photonic platforms. To simultaneously reach a high scattering efficiency and a near-unitary modal overlap with optical fibers, we make use of self-imaging gratings designed with a negative diffraction angle. To ensure high directionality of the diffracted light, we take advantage of a metal back-reflector patterned underneath the grating structure by cryogenic deep reactive ion etching of the silicon handle. Using silicon nitride as a testbed material, we experimentally demonstrate coupling efficiency up to − 0.55 dB in the telecom C-band with high chip-scale device yield. [ABSTRACT FROM AUTHOR]

This paper introduces a beam‐scanning holographic antenna composed of a substrate‐integrated waveguide (SIW) feeding structure and a rectangular microstrip array. The antenna innovatively combines holographic theory with liquid crystal electrical tunability to realize single‐frequency large‐angle beam scanning function which can effectively solve the problem of beamforming reconfiguration in traditional array antenna systems. In this paper, the variation of dielectric constant of liquid crystal under different bias voltages is quantitatively analyzed. Additionally, the beam forming technology is analyzed under hologram amplitude weighting theory. The relevant theories are verified by manufacturing and testing. The prototype antenna achieves the ultra‐wide beam scanning angle of −63° to 63° at 36 GHz. [ABSTRACT FROM AUTHOR]

The polarization properties of a two-channel spatial AO filter based on diffraction into two symmetric Bragg orders have been studied. A regime is demonstrated where during Fourier processing of an image, the contours in different channels are formed in different polarizations and at different acoustic frequencies. This regime was confirmed experimentally on the basis of optical Fourier processing of an image transmitted by radiation with an optical wavelength of 0.63 μm. As a spatial frequency filter, an AO cell manufactured of paratellurite was used. This made it possible to form the image contour in one channel at a sound frequency of 34 MHz and in another channel at a frequency of 42 MHz. [ABSTRACT FROM AUTHOR]

In this work, we used femtosecond‐laser direct writing to fabricate two kinds of modified structures with opposite refractive‐index changes to build fork‐grating configurations in z‐cut LiNbO3 (LN) crystals. Experimental and simulation results indicate that the fork grating combined with the modified area of the refractive index increased and refractive index decreased produces a more effective diffraction effect at 532 nm. The diffraction results of these fork gratings have been investigated. Compared with the fork grating only with the refractive‐index‐decreased filaments, when the incident beam is at transverse magnetic, transverse electric, and circular polarizations, the diffraction efficiency is improved by 5.3%, 4.3%, and 9.6%, respectively. Our work provides a new perspective for improving the diffraction efficiency of fork gratings in LN crystals. [ABSTRACT FROM AUTHOR]

Recent advances in far-infrared detector technology have led to increases in raw sensitivity of more than an order of magnitude over previous state-of-the-art detectors. With such sensitivity, photon noise becomes the dominant noise component, even when using cryogenically cooled optics, unless a method of restricting the spectral bandpass is employed. The leading instrument concept features reflecting diffraction gratings, which post-disperse the light that has been modulated by a polarizing Fourier transform spectrometer (FTS) onto a detector array, thereby reducing the photon noise on each detector. This paper discusses the development of a cryogenic (4 K) diffraction grating spectrometer that operates over the wavelength range of 285 to 500 μm and was used to post-disperse the output from a room-temperature polarizing FTS. Measurements of the grating spectral response and diffraction efficiency are presented as a function of both wavelength and polarization to characterize the instrumental performance. [ABSTRACT FROM AUTHOR]

Polarized holographic properties play an important role in the holographic data storage of traditional organic recording materials. In this study, reduced graphene oxide (RGO) was introduced into a phenanthraquinone-doped polymethylmethacrylate (PQ/PMMA) photopolymer to effectively improve the orthogonal polarization holographic properties of the material. Importantly, the lateral size of RGO nanosheets has an important influence on the polymerization of MMA monomers. To some extent, a larger RGO diameter is more conducive to promoting the polymerization of MMA monomers and can induce more PMMA polymers to be grafted on its surface, thus obtaining a higher PMMA molecular weight. However, too large of a RGO will lead to too much grafting of the PMMA chain to shorten the length of a single PMMA chain, which will lead to the degradation of PQ/PMMA holographic performance. Compared with the original PQ/PMMA, the diffraction efficiency of the RGO-doped PQ/PMMA photopolymer can reach more than 11.4% (more than 3.5 times higher than the original PQ/PMMA), and its photosensitivity is significantly improved by 4.6 times. This study successfully synthesized RGO-doped PQ/PMMA high-performance photopolymer functional materials for multi-dimensional holographic storage by introducing RGO nanoparticles. Furthermore, the polarization holographic properties of PQ/PMMA photopolymer materials can be further accurately improved to a new level. [ABSTRACT FROM AUTHOR]

Polymer systems induced by the reaction between monomers and photo-initiators play a crucial role in the formation of volume-phase gratings. In this paper, we fabricated a dual-photo-initiator photopolymer by doping EY (Eosin Yellow) molecules into a TI (Titanocene, Irgacure 784@BASF) dispersed PMMA (poly-[methyl methacrylate]) substrate system, with the aim of promoting the diffusion and polymerization processes in volume holographic storage. The two-wave interference system is adopted to record a permanent grating structure in our materials. The temporal diffraction variations of photopolymerization (during the interference exposure) and dark diffusion (after the interference exposure) processes have been investigated and analyzed. Aiming to analyze the influence of EY doping ratios on holographic performances, some key parameters were examined in the experiment. We first measured the temporal evolution of diffraction efficiency, then an exponential fitting was adopted to obtain the response time. Finally, the angular selectivity was evaluated by the Bragg condition after holographic recording. Also, the temporal evolution of each component is described by the nonlocal polymerization-driven diffusion model with a dual-photo-initiator composition, theoretically. Furthermore, we experimentally achieved the holographic grating enhancement in both the dark diffusion and photopolymerization processes by doping appropriate EY concentrations, respectively. This work provides a foundation for the acceptability of TI&EY/PMMA polymers in further holographic storage research. [ABSTRACT FROM AUTHOR]

In this paper, we employ gauge/gravity duality to investigate the string breaking and melting of doubly-heavy tetraquark that includes two heavy quarks and two light antiquarks in a holographic model at finite temperature. Firstly, four different configurations of QQ q ¯ q ¯ are studied at different separation distances of the heavy quarks at finite temperatures. At high temperature, QQ q ¯ q ¯ will melt at certain distances and the screening distance has been given for different temperatures. As the temperature continues to increase, some configurations of doubly-heavy tetraquark can not exist. Furthermore, we investigate three decay modes of QQ q ¯ q ¯ and compare the potential energy of QQ q ¯ q ¯ with that of QQq at finite temperature. [ABSTRACT FROM AUTHOR]

This article provides an overview of advancements in liquid crystal (LC) technology for augmented reality (AR) and virtual reality (VR) devices. It discusses the importance of LC technology in improving visual quality and transitions in AR/VR devices, particularly in lens components. The article also highlights the potential of LC materials for the next generation of AR devices, while acknowledging challenges related to alignment and overcoating. It concludes by emphasizing the need for further research and development in optimizing these materials. The article is a valuable resource for library patrons researching this specific topic. [Extracted from the article]

Conventional volume holographic waveguide display devices have the disadvantage of low optical efficiency, making it difficult to meet the needs of outdoor applications. Back‐coupling loss (BCL) can severely decrease the optical efficiency of VHG‐based waveguide systems and thin substrate and angular selectivity of the volume holographic grating (VHG) are the two main reasons of BCL. In this paper, a simple and effective double‐layer waveguide system is proposed to degrade BCL. The simulation results show that the optical efficiency of the double‐layer waveguide system is improved from 5.57% of the single‐layer waveguide to 7.41% of the double‐layer waveguide. [ABSTRACT FROM AUTHOR]

This paper introduces an AR‐HUD system based on a polarization volume grating (PVG) waveguide. The PVG waveguide is optimized to achieve a uniform exit pupil. To verify its performance, an AR‐HUD display system was constructed. The display system achieves a 10×5°field of view at an exit pupil distance of 300mm, boasting a light efficiency of 5.02% and a contrast ratio of 21:1. [ABSTRACT FROM AUTHOR]

The dependence of the change in the components of the inverse permittivity tensor of a cubic photorefractive Bi12SiO20 crystal on the direction of the wave vector of holographic grating in the crystal coordinate system has been studied. It is shown that, when recording a phase hologram, the largest change in the refractive index of Bi12SiO20 crystal is attained when the holographic grating wave vector is oriented along symmetrically equivalent 〈111〉 directions. The maximum possible modulation amplitude of the refractive index of a holographic grating with the wave vector oriented along the 〈110〉 directions is found to exceed that in the case of orientation along the 〈100〉 directions. The components of the inverse permittivity tensor of Bi12SiO20 crystal were calculated taking into account that a phase hologram is recorded under linear electro-optic, photoelastic, and inverse piezoelectric effects. [ABSTRACT FROM AUTHOR]

Augmented reality (AR) displays, as the next generation platform for spatial computing and digital twins, enable users to view digital images superimposed on real-world environment, fostering a deeper level of human-digital interactions. However, as a critical element in an AR system, optical combiners face unprecedented challenges to match the exceptional performance requirements of human vision system while keeping the headset ultracompact and lightweight. After decades of extensive device and material research efforts, and heavy investment in manufacturing technologies, several promising waveguide combiners have been developed. In this review paper, we focus on the perspectives and challenges of optical waveguide combiners for AR displays. We will begin by introducing the basic device structures and operation principles of different AR architectures, and then delve into different waveguide combiners, including geometric and diffractive waveguide combiners. Some commonly used in-couplers and out-couplers, such as prisms, mirrors, surface relief gratings, volume holographic gratings, polarization volume gratings, and metasurface-based couplers, will be discussed, and their properties analyzed in detail. Additionally, we will explore recent advances in waveguide combiner design and modeling, such as exit pupil expansion, wide field of view, geometric architectures of waveguide couplers, full-color propagation, and brightness and color uniformity optimization. Finally, we will discuss the bottlenecks and future development trends in waveguide combiner technologies. The objective of this review is to provide a comprehensive overview of the current state of waveguide combiner technologies, analyze their pros and cons, and then present the future challenges of AR displays. [ABSTRACT FROM AUTHOR]

Using direct laser lithography and wet etching of polished vicinal Si(111) wafers, a technology was developed and diffraction gratings 500 grooves/mm with a blaze angle of 4° were fabricated. The manufacturing process of a reflective Si-grating with the triangular profile (sawtooth) can be divided into four main steps: (1) obtaining a pattern of a protective mask for grooves etching; (2) anisotropic etching of grooves in KOH solution; (3) etching to smooth the grating profile and polish the surface of working facets; (4) coating to increase reflectivity. The samples obtained were characterized using scanning electron microscopy and atomic force microscopy methods to determine the shape of the groove profile and roughness: the shape turned out to be close to the ideal triangular, and the RMS roughness was less than 0.3 nm. Using PCGrateTM software and taking into account the measured real groove profile, the diffraction efficiency of gratings operating in classical and conical mounts in soft-X-ray and extreme ultraviolet radiation has been simulated. The obtained efficiency values are close to the record ones for the corresponding spectral range and the Au-coating of the grating. [ABSTRACT FROM AUTHOR]

High refractive index polymers (HRIPs) are widely used in lenses, waveguide, antireflective layer and encapsulators, especially the advanced fields of augmented/virtual reality (AR / VR) holographic technology and photoresist for chip manufacturing. In order to meet the needs of different applications, the development of HRIPs focuses not only on the increase in refractive index but also on the balance of other properties. Sulfur‐containing high refractive index polymers have received extensive attention from researchers due to their excellent properties. In recent years, not only ultrahigh refractive index sulfur‐containing polymers have been continuously developed, but also low dispersion, low birefringence, high transparency, good mechanical properties, and machinability have been studied. The design of HRIPs is generally based on formulas and existing experience. In fact, molecular structure and properties are closely related. Mastering the structure–property relationship helps researchers to develop high refractive index polymer materials with balanced properties. This review briefly introduces the preparation methods of sulfur‐containing high refractive index polymers, and summarizes the structure–property relationship between the sulfur‐containing molecular structure and optical properties, mechanical properties, thermal properties, etc. Finally, the important role of synergistic effect in the synthesis of HRIPs and the prospect of future research on HRIPs are proposed. [ABSTRACT FROM AUTHOR]