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Acoustic holography (AH) provides a promising technique for arbitrary acoustic field reconstruction, supporting many applications like robotic micro-nano manipulation, neuromodulation, volumetric imaging, and virtual reality. In AH, three-dimensional (3D) acoustic fields quantified with complex-valued acoustic pressures are reconstructed by virtue of two-dimensional (2D) acoustic holograms. Phase-only hologram (POH) is recently regarded as an energy-efficient way for AH, which is typically implemented by a dynamically programmable phased array of transducers (PATs). As a result, spatiotemporal precise acoustic field reconstruction is enabled by precise, dynamic, and individual actuation of PAT. Thus, 2D POH is required per arbitrary acoustic fields, which can be viewed as a physical inverse problem. However, solving the aforementioned physical inverse problem in numerical manners poses challenges due to its non-linear, high-dimensional, and complex coupling natures. The existing iterative algorithms like the iterative angular spectrum approach (IASA) and iterative backpropagation (IB) still suffer from speed-accuracy trade-offs. Hence, this paper explores a novel physics-iterative-reinforced deep learning method, in which frequency-argument contrastive learning is proposed facilitated by the inherent physical nature of AH, and the energy conservation law is under consideration. The experimental results demonstrate the effectiveness of the proposed method for acoustic field reconstruction, highlighting its significant potential in the domain of acoustics, and pushing forward the combination of physics into deep learning. [ABSTRACT FROM AUTHOR]

The increasing demand for functional nanodevices in sustainable energy applications necessitates the development of innovative approaches. In this study, we present the fabrication and characterization of three-dimensional (3D) structures coated with titanium dioxide (TiO 2) nanorods (NRs). These novel devices are created through the integration of four distinct techniques, multi-photon lithography, post-thermal treatment, pulsed laser deposition, and an aqueous chemical growth, enabling their unique properties and functionalities in photocatalysis. The photocatalytic performance of the 3D devices is evaluated through the degradation of organic pollutants, such as methylene blue and stearic acid, showcasing their efficiency in reducing pollutant concentrations. The devices demonstrate a remarkable decomposition coefficient (k = 0.059 min − 1 ), highlighting their enhanced photocatalytic efficiency. Additionally, we propose a rapid fabrication technique using 3D holographic printing to create large-area TiO 2 -coated micro-structured photocatalytic devices at the mesoscale regime. This approach increases the active surface area, further enhancing the devices' photocatalytic capabilities. By combining additive micro-manufacturing, TiO 2 NR coating, and holographic printing, our work introduces a promising avenue for the development of advanced nanodevices with superior photocatalytic performance in sustainable energy applications. [ABSTRACT FROM AUTHOR]

Lensless in-line holography is widely used to obtain depth information on pathological tissues and biological cells to enable noninvasive analysis, due to low cost and large field-of-view. However, existing systems suffer from crosstalk dilemma of twin-image that limit their capability to achieve high-resolution phase imaging with a single measurement, especially in the presence of noise. In this Letter, we propose a physics-guided frequency-aware network (FA-PGNet) for single-shot lens-free holographic reconstruction. The FA-PGNet method uses frequency-level supervision to balance the high- and low-frequency information between images and gradually obtained reliability results by incorporating a physical model. With the co-addition of frequency-aware and physics-guided, it can easily tackle the twin-image and speckle noise, with 5.88 dB improvement on the peak signal-to-noise ratio and 6-fold reduction on the uncertainty of the imaging system. Optical experiments demonstrate that the FA-PGNet allows access to complex features of microscopic cells with high resolution. We believe that the proposed method provides a powerful tool for single-shot cell imaging. [ABSTRACT FROM AUTHOR]

We proposed a method to measure the topological charge of a vortex beam by using the self-rotating beam phase in this Letter. We investigated the far-field intensity patterns of the vortex beams passing through a phase hologram of the self-rotating beam with n = +2 theoretically and experimentally. The results demonstrate that the far-field intensity patterns cannot exhibit bright stripes when the topological charge of the vortex is positive (i.e., n ⋅ l > 0) and the calculated ratio relationship ξ can be used to identify the topological charge of the vortex beam. Differently, it can be found that the far-field intensity patterns exhibit several bright stripes when the topological charge of the vortex is negative (i.e., n ⋅ l < 0) and the number N of the bright stripes is equal to |l|−1(l represents the topological charge of the vortex beam). The experimental results are in good agreement with the theoretical ones. This method may inspire further research in the field of self-rotating beams. [ABSTRACT FROM AUTHOR]

We describe the details of a digital holographic microscopy diagnostic capable of quantifying both the topography and velocity of a km/s object with adjustable temporal sensitivity. This technique involves spatially multiplexing a double pulse reflected from a target with reference beams of precisely known temporal separation. [ABSTRACT FROM AUTHOR]

Metasurfaces are sub-wavelength patterned layers for controlling waves in physical systems. In optics, metasurfaces are created by materials with different dielectric constants and are capable of unconventional functionalities. We develop a deep-learning framework for Dirac-material metasurface design for controlling electronic waves. The metasurface is a configuration of circular graphene quantum dots, each created by an electric potential. Employing deep convolutional neural networks, we show that the original scattering wave can be reconstructed with fidelity over 95%, suggesting the feasibility of Dirac electron holography. Additional applications such as plane wave generation and designing broadband and multi-functionality electronic metasurface in graphene are illustrated. [ABSTRACT FROM AUTHOR]

Metasurface holography is a significant technology for the development of ultrathin optical devices. Multichannel holography has received close attention due to its applications in increasing information capacity and optical secret sharing. However, existing design methods for multichannel holography mainly focus on interleaved metasurface imaging in the vertical direction, which will inevitably suffer from the unexpected crosstalk affecting imaging quality. This work presents noninterleaved spin-selective metasurfaces by combining the geometric phase and the propagating phase. It can achieve independent phase control on two orthogonal circular polarizations and image at the desired angle. As a proof-of-concept, two broadband plasmonic metasurfaces are designed for multichannel holographic imaging in the near-infrared band (800–1200 nm). When two orthogonal circularly polarized waves are normally incident, the first plasmonic metasurface displays two different holograms in the vertical direction, thus achieving dual-channel imaging, and the second plasmonic metasurface can make two holograms deflected to the desired angle. It means that these two holograms can be displayed without overlapping for a linearly polarized wave, and the orientable three-channel holographic imaging is realized. Our work provides a general and compact scheme for multichannel orientable holographic imaging. [ABSTRACT FROM AUTHOR]

The measurement of the spatial distribution of the nearly monocyclic terahertz (THz) fields by a raster scanning diaphragm is the widely used approach in THz pulse time-domain holography (PTDH) applied in imaging, optical component design, and wavefront sensing tasks. However, it is historically plagued by a compromise between the balance between the signal-to-noise ratio (SNR) and resolution. To address this challenge and keep both parameters at a high level, we proposed to replace the scanning aperture with the scanning module containing a conjugated diaphragm and lens. This solution allowed us for the first time to experimentally investigate the spatio-temporal dynamics of a Gauss–Bessel beam generated in a widespread low-energy THz system based on a femtosecond laser with a pulse energy of around a dozen nanojoules and a repetition rate of tens of megahertz. In particular, this allowed us to observe the temporal spectrum of the THz Gauss–Bessel field at the beam periphery with SNR ≈ 0.5 , which was not possible using a conventional raster scanning system. A careful numerical analysis of the proposed solution reveals a signal enhancement in the spectral domain of approximately 2.5 times compared to the THz PTDH raster scan detection employing only a diaphragm. Moreover, we have shown that the given solution ensures the temporal profiles remain unaffected by the quadratic phase aberration experienced in conventional raster field scanning with only a single aperture. [ABSTRACT FROM AUTHOR]

Holographic display is considered the holy grail of photorealistic three-dimensional (3D) visualization technology because it can provide arbitrary wavefronts related to the essential visual cues of 3D images. Metasurfaces with exceptional high-pixel light modulation capability are increasingly favored for implementing high-quality 3D holography. However, current 3D metasurface holography always has some trade-offs among lots of algorithmic data, acceptable time, image quality, and structure complexity. Therefore, the development of a high-efficiency 3D metasurface holography device is still necessary to meet the increasing high space bandwidth product (SBP) of 3D technology. Here, based on the holographic-lens (HL) computer-generated hologram (CGH) algorithm, we experimentally demonstrate a new 3D metasurface holography device that integrates the 3D image phase cues and multiple layers of virtual lenses with different focal lengths, which exhibits significant capabilities in terms of ultra-high spatial pixel modulation and the generation of high-quality 3D holography characterized by high-efficiency, broadband response, low-crosstalk, and reduced acceptable time. The HL-CGH algorithm was efficiently integrated into parameter-optimized α-Si nanopillar meta-atoms, enabling enhanced visualization of 3D clues in a lens-free system. The prepared 3D HL-metasurface holography presented the presence of multiple depths of a 3D holographic image across a broad spectral range (400–900 nm), providing enhanced 3D visual cues. Our work provides a new perspective on designing metasurface-driven high-SBP 3D holography. [ABSTRACT FROM AUTHOR]

The compactness and particular optical design make metasurface a competitive candidate for holographic display and storage. Recently, the selection and optimization for the used metasurface structures and types have become research spots. Now the most researched and demonstrated meta-holograms are often based on discrete structures, which can achieve high efficiency but comparatively narrow working bandwidths or a wide wavelength range but low power efficiency. Therefore, contemporary meta-holograms struggle for realizing simultaneous broadband and high efficiency. In this paper, all-dielectric quasi-continuous metasurfaces composed of nanostrips are introduced to expand the operating bandwidth for high efficiency meta-holography. Benefiting from the associated Pancharatnam–Berry phase, the nanostrips with spatially orientation angles continuous changes can realize arbitrary phase modulation. For the first time, the average power efficiency of a meta-hologram is experimentally measured to be 56.63% over a broad wavelength band ranging from 500 to 1000 nm. In addition, based on this kind of all-dielectric quasi-continuous nanostrips, we also design and experimentally achieve multicolor three-dimensional (3D) holographic images. Actually, such all-dielectric quasi-continuous methodology proposed here can be used to design other functional meta-devices, including optical metalens, nanoprinting, and information encryption. [ABSTRACT FROM AUTHOR]

This paper proposes a distorted hologram data repair approach for sound field reconstruction. In this approach, an equivalent source model is established by placing a set of equivalent sources near the hologram surface to represent the measured hologram pressures. Each hologram pressure is simultaneously assigned an indicator to describe whether its measurement is corrupted by errors or not. This model is then formulated within a modal framework by utilizing the modes generated through the singular value decomposition of the transfer matrix between the hologram and nearby equivalent source surfaces. Subsequently, the indicators and modal coefficients are assigned the 0–1 and Gaussian prior distributions, respectively, and their posterior distributions are derived using the Bayesian method. The means of the posterior distributions are calculated to discriminate corrupted measurements and repair distorted hologram pressures. Repaired hologram pressures are finally utilized for reconstructions using the equivalent source method. Results from both numerical simulations conducted under various parameter settings and two experiments demonstrate the effectiveness of the proposed approach in automatically discriminating all the corrupted measurements and accurately repairing the distorted hologram pressures. Furthermore, the accuracy of the reconstructions using the repaired hologram pressures is comparable to that achieved with the correctly measured pressures. [ABSTRACT FROM AUTHOR]

The twin image-free phase reconstruction is still a challenge with single-shot inline holographic systems. Existing solutions mostly are based on the inverse problem approaches or alternating projections. However, there exists a trade-off between phase retrieval and twin image elimination. Recent studies have introduced a hybrid method involving both the approaches to mitigate this trade-off. Following these works, we propose a single-shot sparsity-assisted iterative phase retrieval approach that applies a sparsity constraint in the object domain and formulates phase retrieval as a minimization problem. We demonstrate lensless digital inline holographic microscopy for imaging transparent and weakly scattering biological samples over a large field-of-view of ∼ 29 mm 2. The proposed method achieves high fidelity phase reconstruction with faster convergence compared to the existing single-shot phase retrieval methods. We further demonstrate the phase quantification of label-free biological samples, such as cervical cells and RBCs, to highlight the potential of our technique in clinical applications. [ABSTRACT FROM AUTHOR]

When a perturbed periodic oscillation dephases, the system edits it to retrieve the original clock. The inherent clock born during retrieval is the time crystal. Time crystals have been explored for five decades, and only one inherent clock was detected in biological and artificial systems. Only one type of atom is used in those time crystals, but two or more atom types would lead to multi-functional and programmable time crystals. No such concept was ever conceived. Here, we demonstrate a multi-clock time crystal or a polyatomic time crystal in the brain neuron-extracted microtubule nanowire using dielectric resonance and quantum optics experiments. Earlier, one used to artificially reset the phase of an inherent clock to find a time crystal. Instead, we map how a biomaterial spontaneously generates distinct new clocks at many time domains at a time. We observe multiple time-symmetry-breaking events at a time. Moreover, unlike conventional time crystal research, we searched for polyatomic time crystals at least 103 orders lower than the excitation frequency region. Conventional time crystals could be rejected, arguing that inherent clocks born after the breaking of time symmetry are harmonics of the external input, and such an argument will not hold for us. Moreover, quantum experiments revealed a method to synthesize and fuse distinct clocks in one hologram as a polyatomic time crystal and project it like an antenna meters away. The discovery of material-like holographic engineering of polyatomic time crystals would make them useful. [ABSTRACT FROM AUTHOR]

Guide star assisted wavefront shaping techniques have been exploited for focusing and imaging through turbid media by addressing a scatter inverse pattern. However, the turbid medium is required to be steady before finding the proper correction pattern, which limits applications in focusing and imaging through dynamic media, such as turbid water or blood. This study proposes a holography-based dual-polarization computational wavefront shaping method for imaging objects at variant depths behind dynamic turbid media. The orthogonal polarized output speckles of a point source (considered as a guide star) and an object are simultaneously recorded in holograms in separate regions of a single CCD camera. The holograms of the point source and object are subjected to the same distortion regardless of whether the media is static or dynamic. The hologram of the point source is used to determine the correction phase pattern for the distortion, while that of the object is used to record the complex scattered wavefront of the object. To reconstruct a clear object image, the wavefront of the scattered object is digitally corrected using the correction phase pattern and is then transferred to the image plane by calculating the transmission of the angular spectrum. Benefiting from the autofocusing feature of digital holography, objects at different depths can be recovered from a single shot hologram pair. The potential applications of the proposed method in diverse dynamic scattering media are demonstrated by imaging through a moving diffuser, turbid water, and pig blood with optical depth beyond 10. [ABSTRACT FROM AUTHOR]

In this paper, a series of impulse response functions between acoustic quantities on the source plane and particle velocity on the hologram plane are derived. In virtue of these functions, real-time nearfield acoustic holography (RT-NAH) is extended from pressure-based to particle velocity. Pressure, normal velocity, acceleration, and displacement radiated from planar sources can be reconstructed by measuring time-dependent particle velocity signals on the hologram plane. A simulation of an excited aluminum plate is performed to evaluate the difference in accuracy between RT-NAHs based on pressure and based on particle velocity. This study also examines the impact of impulse response functions on the reconstruction results, allowing for detailed analysis of the reconstruction accuracy based on these functions. The simulation results demonstrate that using RT-NAH based on particle velocity obtains significantly higher-accuracy reconstruction results when reconstructing normal velocity and displacement and slightly more accurate reconstructed pressure and normal acceleration. [ABSTRACT FROM AUTHOR]

Optical systems use acousto-optic deflectors (AODs) mostly for fast angular scanning and spectral filtering of laser beams. However, AODs may transform laser light in much broader ways. When time-locked to the pulsing of low repetition rate laser amplifiers, AODs permit the holographic reconstruction of 1D and pseudo-two-dimensional (ps2D) intensity objects of rectangular shape by controlling the amplitude and phase of the light field at high (20–200 kHz) rates for microscopic light patterning. Using iterative Fourier transformations (IFTs), we searched for AOD-compatible holograms to reconstruct the given ps2D target patterns through either phase-only or complex light field modulation. We previously showed that phase-only holograms can adequately render grid-like patterns of diffraction-limited points with non-overlapping diffraction orders, while side lobes to the target pattern can be cured with an apodization mask. Dense target patterns, in contrast, are typically encumbered by apodization-resistant speckle noise. Here, we show the denoised rendering of dense ps2D objects by complex acousto-optic holograms deriving from simultaneous optimization of the amplitude and phase of the light field. Target patterns lacking ps2D symmetry, although not translatable into single holograms, were accessed by serial holography based on a segregation into ps2D-compatible components. The holograms retrieved under different regularizations were experimentally validated in an AOD random-access microscope. IFT regularizations characterized in this work extend the versatility of acousto-optic holography for fast dynamic light patterning. [ABSTRACT FROM AUTHOR]

Beam shaping—the ability to engineer the phase and the amplitude of massive and massless particles—has long interested scientists working on communication, imaging, and the foundations of quantum mechanics. In light optics, the shaping of electromagnetic waves (photons) can be achieved using techniques that include, but are not limited to, direct manipulation of the beam source (as in x-ray free electron lasers and synchrotrons), deformable mirrors, spatial light modulators, mode converters, and holograms. The recent introduction of holographic masks for electrons provides new possibilities for electron beam shaping. Their fabrication has been made possible by advances in micrometric and nanometric device production using lithography and focused on ion beam patterning. This article provides a tutorial on the generation, production, and analysis of synthetic holograms for transmission electron microscopy. It begins with an introduction to synthetic holograms, outlining why they are useful for beam shaping to study material properties. It then focuses on the fabrication of the required devices from theoretical and experimental perspectives, with examples taken from both simulations and experimental results. Applications of synthetic electron holograms as aberration correctors, electron vortex generators, and spatial mode sorters are then presented. [ABSTRACT FROM AUTHOR]

Digital coding metasurfaces composed of subwavelength meta-atoms can flexibly control electromagnetic waves to achieve holography, which has great potential in millimeter-wave imaging systems and data storage. In this paper, we propose a 3-bit reflective digital coding metasurface. The incident linearly polarized waves can be transformed into cross-polarized components with distinct phase responses by adjusting the rotational and open angles of the coding elements. The 3-bit phase performance can be retained over a wide bandwidth from 12 to 18 GHz by simultaneously changing the rotational and open angles. Based on the proposed broadband metasurface, broadband holography is successfully demonstrated with the optimization of a modified Gerchberg–Saxton algorithm. As a proof of concept, five schemes with different holograms integrating the letters "S," "E," "U," "X," and "Z" are simulated from 12 to 18 GHz. Good simulation results validate the performance of the proposed broadband holography, showing a relative bandwidth of 40%. Two prototypes superposing the holograms of letters "U" and "X" are fabricated and measured in a near-field microwave anechoic chamber. The experimental results corroborate well with simulated results, further supporting the demonstration. We believe that the proposed broadband holography based on the digital coding metasurface paves a way to wideband applications for microwave imaging, information processing, and holographic data storage. [ABSTRACT FROM AUTHOR]

Digital holography requires precise phase analysis without wavefront aberration from defocusing errors. While the auto-contrast method is generally advantageous for refocusing, its accuracy suffers in low contrast conditions. Here, we suggest a simple phase analysis approach applying phase-detection autofocusing (PDAF) using a Fourier operation and the angular spectrum method to achieve fast and accurate refocusing even with high transmittance samples. The speed and sub-nano accuracy of the proposed method along with its quantitative autofocusing capability make it well suited for numerical digital holography reconstruction. Phase analysis with the PDAF technique has sensitivity to 0.1 nm changes in the focusing distance within the light source wavelength. In the reconstruction process, this method causes no wavefront distortion. The refocus calculation time using the focus calibration function obtained through the PDAF method is 0.012 s, enabling a real-time refocus correction of 83 fps in digital video holography. We performed refractive index measurements of Boro33 plates with high transmittance to interpret the physical meaning of the corrected focal distances and obtained a refractive index accuracy of 0.001. We then applied a real-time digital holographic measurement system and found that the PDAF technique removed dynamic phase fluctuation, an issue that cannot be solved by phase unwrapping. [ABSTRACT FROM AUTHOR]

A correlation holography technique for quantitative phase imaging from scattered depolarized light is proposed and experimentally demonstrated. To implement this technique, we exploit the depolarization of scattered light with the higher-order Stokes correlation. The higher-order Stokes correlation along with the two-step phase-shifting method is utilized to retrieve the complex Fourier coefficient, this subsequently supports the recovery of the phase in the correlation holography with the fourth-order correlation. A detailed theoretical framework is developed and is also supported by numerical simulation and experimental tests. The applicability of the proposed technique is experimentally demonstrated by quantitatively reconstructing different phase objects from the scattered depolarized light. [ABSTRACT FROM AUTHOR]

Complex vector light modes, characterized by a non-uniform transverse polarization distribution, have pervaded a wide range of research fields. In this study, we propose an approach that enables the simultaneous generation of multiple vector beams based on a spatially segmented digital hologram and two or more cascaded beam displacers. More precisely, an input beam is separated into multiple parallel copies spatially separated, which are then sent to the center of each segmented hologram, enabling independent modulation of each beam. The modulated beams are then judiciously recombined with a beam displacer to generate multiple vector modes in a simultaneous way. We demonstrated our technique with two arbitrary vector modes but the technique can be easily extended to more by inserting additional beam displacers. To assess the quality of the generated vector modes, we employed Stokes polarimetry to reconstruct their transverse polarization distribution and to measure their degree of non-separability. We envision that this technique will find significant applications in various fields, including optical communications, optical sensing, and optical tweezers to mention a few. [ABSTRACT FROM AUTHOR]

In this paper, we propose an approach that combines wavefront encoding and convolutional neuronal network (CNN)-based decoding for quantitative phase imaging (QPI). Encoding is realized by defocusing, and decoding by CNN trained on simulated datasets. We have demonstrated that based on the proposed approach of creating the dataset, it is possible to overcome the typical pitfall of CNN learning, such as the shortage of reliable data. In the proposed data flow, CNN training is performed on simulated data, while CNN application is performed on real data. Our approach is benchmarked in real-life experiments with a digital holography approach. Our approach is purely software-based: the QPI upgrade of a bright-field microscope does not require extra optical components such as reference beams or spatial light modulators. [ABSTRACT FROM AUTHOR]

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

In digital holography, extracting the +1-order spectrum accurately and making full utilization of the spatial bandwidth of the CCD sensor are essential for high-resolution and artifacts-free quantitative phase imaging. In this paper, using the light intensity symmetry of the Gaussian laser beam, we delicately eliminate the zero-order spectrum by means of subtraction of two off-axis hologram spectra acquired by symmetrically deflecting the reference beam. Therefore, the +1-order spectrum can be extracted accurately even if it is completely overlapped with the zero-order spectrum. Compared with phase-shifting methods, such as pi-phase and random phase, which require accurate control or calculation of the phase-shifting amount, this proposed method does not need to precisely control the deflection angle of reference beam. Being achievable the maximum utilization of half-space bandwidth of the CCD sensor, the proposed method has realized high-resolution imaging demonstrated by the experimental results of three specimens. This method has general applications in digital holography, such as eliminating the zero-order spectrum and extracting the +1-order spectrum. [ABSTRACT FROM AUTHOR]

In this paper, an approach is proposed toward two-dimensional (2D) beam tailoring in the terahertz band based on programmable metasurface loaded with liquid crystals. Specifically, a 1-bit reflective metasurface element is designed with switchable phase responses, and subsequently, an individually controllable metasurface array in 2D fashion is achieved by pixelating the metallic reflection back plate. As typical examples, programmable metasurfaces operating around 94 and 220 GHz are developed, respectively, and both simulation and experimental results confirm the powerful abilities of the metasurfaces in 2D wide-angle beam manipulations. In addition, the proposed method has advantages of wide frequency range, low cost, and high reliability, implying significant application prospects in terahertz reconfigurable intelligent surfaces and holographic imaging. [ABSTRACT FROM AUTHOR]

Aided by computer generated holography, holographic optical tweezers enable manipulation of particles and objects with exceptional versatility. The responsiveness of the manipulation is often hindered by the speed of holograph generation, especially when the number of manipulated objects is high. Here, we propose an optimized hologram generation method with an improved iterative algorithm utilizing parallel computation with graphic processing units. The algorithm requires fewer iterations to produce high-quality holograms than established methods, such as weighted Gerchberg–Saxton algorithm, leading to a responsive and stable micromanipulation. This method expands the capabilities of holographic optical tweezers and provides more responsive traps in micro-manipulation. [ABSTRACT FROM AUTHOR]

Multiplexing technologies can be used as a platform for low-cost, high-performance, and large-capacity holographic displays and data storage systems. In this paper, a polarization multiplexed method is proposed to realize two different information channels under orthogonally linear-polarized incidences utilizing the coding metasurface. Based on the modified weighted Gerchberg–Saxton (GSW) algorithm, a two-bit coding metasurface is designed with a set of double-layer cross-type meta-atoms to encode the holographic phase information, which can reflect two independent holographic images with respect to different incident polarization. The experimental results agree well with the numerical simulations and the theoretical predictions, which make the proposed multiplexed two-bit coding meta-hologram a great potential in numerous applications such as data storage and information processing. [ABSTRACT FROM AUTHOR]

The internal fields in 2.2 nm thick InGaN quantum wells in a GaN LED structure have been investigated by using aberration-corrected off-axis electron holography with a spatial resolution of better than 1 nm. To improve the spatial resolution, different types of off-axis electron holography acquisitions have been used, including pi phase shifting and phase shifting holography. A series of electron holograms have been summed up to simultaneously improve the sensitivity in the measurements. A value of 20% of indium concentration in the quantum wells has been obtained by comparing the deformation measured by dark-field electron holography and geometrical phase analysis to finite element simulations. The electrostatic potential has then been measured by off-axis electron holography. The mean inner potential difference between the InGaN quantum wells and the GaN quantum barriers is high compared to the piezoelectric potential. Due to the improved spatial resolution, it is possible to compare the experimental results to simulations and remove the mean inner potential component to provide a quantitative measurement of the piezoelectric potential. [ABSTRACT FROM AUTHOR]

In the past few years, the venerable field of holographic microscopy has been revitalized by computational data analysis. It is now possible to fit a generative (forward) model of scattering directly to experimentally obtained holograms of complex microscopic objects. This approach enables precision measurements: it allows the motion of colloidal particles and biological organisms to be tracked with nanometer-scale precision and their optical properties to be inferred particle by particle. In this Perspective, we discuss how the model-based inference approach to holographic microscopy has opened up new applications. We also discuss how it must evolve to meet the needs of emerging applications that demand lower systematic uncertainties and higher precision. In this context, we present some new results on how modeling the optical train of the microscope can enable better measurements of the positions of spherical and nonspherical colloidal particles. Finally, we discuss how machine learning might play a role in future advances. Though we do not exhaustively catalog all the developments in this field, we show a few examples and some new results that spotlight open questions and opportunities. [ABSTRACT FROM AUTHOR]

We generated dense mid-air volumetric acoustic holography using a newly developed computation algorithm and experimentally verified its utility for three-dimensional self-positioning via monaural amplitude measurements. We computed the holography by solving an inverse problem where complex amplitudes of ultrasound emissions are to be determined so that the given acoustic amplitude field at a finite set of control points in the workspace could be generated as faithfully as possible. With a one-directional gradient pattern of a 40 kHz ultrasonic field that stretched uniformly toward the depth direction, numerical simulations showed that positioning with an average error less than 3 mm is ideally possible in a 100 mm-sided cubic workspace. We experimentally verified that this error was approximately 8 mm with our custom-made phased array. Our work shows the first example of information systems, where a position-dependent information field is embedded in the environment as a form of holographic wave field that can be sensed by standalone mobile devices. [ABSTRACT FROM AUTHOR]

Digital holography has found applications in many walks of life, from medicine to metrology, due to its ability to measure complex fields. Here, we use the power of digital holography to quantitatively image two-dimensional Transition Metal Dichalcogenides (TMDs) such as MoS2 and WS2 placed on a SiO2/Si substrate and determine their complex refractive indices or layer thicknesses. By considering the different refractive indices of the TMDs as they are thinned down from bulk to monolayers and by holographically capturing both the amplitude and the phase of reflected light, single atomic layers of TMDs, about 0.7 nm thick, can be resolved. Using holography, we also predict the number of layers contained within a thick TMD flake, which shows agreement with results obtained using Atomic Force Microscopy (AFM). A Bland–Altman analysis was performed to compare our experimental results with the standard AFM measurements, yielding a limit of agreement <5 nm for samples with thicknesses ranging from 15 to 60 nm. Our technique is non-contact, non-invasive, does not require scanning, and produces a field of view of a few hundred micrometers by a few hundred micrometers in a single capture. To further our study, we also perform simulations to demonstrate how the thickness of the SiO2 layer and the laser wavelength are critical in optimizing the amplitude and phase response of a two-dimensional material. These simulations can be used as a roadmap to determine the ideal wavelength and SiO2 layer thickness that should be used to accurately determine the refractive index or thickness of any given sample. [ABSTRACT FROM AUTHOR]

Measurement of absorption coefficients of transparent samples is important for their characterization and identification; however, it is challenging to measure low values, e.g., 10−3–10−4 cm−1 with high accuracy. Here, we report a compact photothermal lateral shearing digital holographic device. It is based on the thermal lens effect and a common-path, self-referencing digital holographic microscope comprising a glass plate, probe beam, and a CMOS camera. The change in phase distribution caused by the temperature change due to light absorption is measured from the recorded holograms to extract the sample's absorbance and absorption coefficient. The feasibility of the proposed configuration is validated by the experimental results obtained with different concentrations of gold nanoparticles (AuNPs) in an aqueous solution. Determination of AuNPs concentration in the nM range is performed, and the obtained limits of detection and quantitation are 0.04 nM and 0.13, respectively. The calibration curve is linear at a low concentration range of 0.06–0.95 nM with 1% reproducibility. In addition, the method's versatility is demonstrated by measuring the absorption coefficient of low-loss solvents, such as ethanol and water. The determined absorption coefficients agree with the reported values, confirming that this method provides good spectrometric capabilities, such as high sensitivity and accuracy. [ABSTRACT FROM AUTHOR]

Morphology and motility are essential criteria for assessing sperm viability. However, the human sperm head is small (∼3–4 μm) and requires a relatively high-magnification microscope objective, while the sperm flagella (∼45 μm) are poorly visible with complex 3D properties. Microscopic dynamic observation of intact sperm in 3D is challenging. Conventional inspection methods with a limited depth of field are inadequate for this issue. To provide a solution to this critical need, we develop pixelated polarization-based parallel phase-shifting digital holographic microscopy for the 3D dynamic observation of human sperm. Compared to conventional holographic imaging, this approach can effectively separate the object wavefront and avoid image quality degradation while fully exploiting the spatial bandwidth of the camera. We propose the use of the Stokes parameter reconstruction method to reconstruct the object wavefront and investigate the effect of the sampling interval on the system resolution by spectral analysis. The methodology achieves the retrieval of the 3D trajectory and motion parameters of sperm and reconstructs the sperm head orientation and the thin, highly-dynamic flagellum. The system allows for more comprehensive information on sperm motility and morphology, which is significant for male reproductive research. It also has significant potential for 3D dynamic observation of micro-organisms. [ABSTRACT FROM AUTHOR]

Unlike the holography technique using active sound source arrays, metasurface-based holography can avoid cumbersome circuitry and only needs a single transducer. However, a large number of individually designed elements with unique amplitude and phase modulation capabilities are often required to obtain a high-quality holographic image, which is a non-trivial task. In this paper, the deep-learning-aided inverse design of an acoustic metasurface-based hologram with millions of elements to reconstruct megapixel pictures is reported. To improve the imaging quality, an iterative compensation algorithm is proposed to remove the interference fringes and unclear details of the images. A megapixel image of Mona Lisa's portrait is reconstructed by a 2000 × 2000 metasurface-based hologram. Finally, the design is experimentally validated by a metasurface consisting 30 × 30 three-dimensional printed elements that can reproduce the eye part of Mona Lisa's portrait. It is shown that the sparse arrangement of the elements can produce high-quality images even when the metasurface has fewer elements than the targeted image pixels. [ABSTRACT FROM AUTHOR]

We propose a protocol for compact and efficient synthesis of a random vectorial source with a higher-order Poincaré (HOP) polarization state encoded into the spatial coherence structure. The procedure is based on the complex-random-mode representation of the cross-spectral density matrix and employs a single phase-only spatial light modulator (SLM) and a common path interferometric system for the mode construction. The SLM displays a set of elaborated multiplexed holograms, which both encode the HOP polarization state and determine the statistical properties of the source. We demonstrate that the beam from the synthesized source can be highly robust against obstructions in the propagation path in the sense that the encoded HOP polarization state is well reconstructed in the far field (focal plane) even when an obstacle is introduced to largely block the source. The results are useful for the transmission of polarization-encoded information in complex media. [ABSTRACT FROM AUTHOR]

We report a highly stable and affordable dual-wavelength digital holographic microscopy system based on common-path geometry. A Fresnel biprism is used to create an off-axis geometry, and two diode laser sources with different wavelengths λ1 = 532 nm and λ2 = 650 nm generate the dual-wavelength compound hologram. In order to extend the measurement range, the phase distribution is obtained using a synthetic wavelength Λ1 = 2930.5 nm. Furthermore, to improve the system's temporal stability and reduce speckle noise, a shorter wavelength (Λ2 = 292.5 nm) is used. The feasibility of the proposed configuration is validated by the experimental results obtained with Molybdenum trioxide, Paramecium, and red blood cell specimens. [ABSTRACT FROM AUTHOR]

Quantum mechanics, superfluids, and capillary fluids are closely related: It is thermodynamics that links them. In this paper, the Liu procedure is used to analyze the thermodynamic requirements. A comparison with the traditional method of divergence separation highlights the role of spacetime. It is shown that perfect Korteweg fluids are holographic. The conditions under which a complex field can represent the density and velocity fields of the fluid, and where the complex scalar field becomes a wave function of quantum mechanics, are explored. The bridge between the field and particle representations of a physical system is holography, and the key to holography is the Second Law of Thermodynamics. [ABSTRACT FROM AUTHOR]

Digital holography (DH) is a powerful imaging modality that is capable of capturing the object wavefront information, making it very valuable for diverse scientific research applications. Generally, it requires ample illumination to enable good fringe visibility and a sufficient signal-to-noise ratio. As such, in situations such as probing live cells with minimal light interaction and high-speed volumetric tracking in flow cytometry, the holograms generated with a limited photon budget suffer from poor pattern visibility. While it is possible to make use of photon-counting detectors to improve the hologram quality, the long recording procedure coupled with the need for mechanical scanning means that real-time extremely low-light holographic imaging remains a formidable challenge. Here, we develop a snapshot DH that can operate at an ultra-low photon level (less than one photon per pixel). This is achieved by leveraging a quanta image sensor to capture a stack of binary holographic frames and then computationally reconstructing the wavefront through integrating the mathematical imaging model and the data-driven processing, an approach that we termed PSHoloNet. The robustness and versatility of our DH system are demonstrated on both synthetic and experimental holograms with two common DH tasks, namely particle volumetric reconstruction and phase imaging. Our results demonstrate that it is possible to expand DH to the photon-starved regime, and our method will enable more advanced holography applications in various scientific imaging systems. [ABSTRACT FROM AUTHOR]

The achievement of a flat metasurface has realized extraordinary control over light–matter interaction at the nanoscale, enabling widespread use in imaging, holography, and biophotonics. However, three-dimensional metasurfaces with the potential to provide additional light–matter manipulation flexibility attract only little interest. Here, we demonstrate a three-dimensional metasurface scheme capable of providing dual phase control through out-of-plane plasmonic resonance of L-shape antennas. Under circularly polarized excitation at a specific wavelength, the L-shape antennas with rotating orientation angle act as spatially variant three-dimensional tilted dipoles and are able to generate desire phase delay for different polarization components. Generalized Snell's law is achieved for both in-plane and out-of-plane dipole components through arranging such L-shape antennas into arrays. These three-dimensional metasurfaces suggest a route for wavefront modulation and a variety of nanophotonic applications. [ABSTRACT FROM AUTHOR]

Single-shot reconstruction of the inline hologram is highly desirable as a cost-effective and portable imaging modality in resource-constrained environments. However, the twin image artifacts, caused by the propagation of the conjugated wavefront with missing phase information, contaminate the reconstruction. Existing end-to-end deep learning-based methods require massive training data pairs with environmental and system stability, which is very difficult to achieve. Recently proposed deep image prior (DIP) integrates the physical model of hologram formation into deep neural networks without any prior training requirement. However, the process of fitting the model output to a single measured hologram results in the fitting of interference-related noise. To overcome this problem, we have implemented an untrained deep neural network powered with explicit regularization by denoising (RED), which removes twin images and noise in reconstruction. Our work demonstrates the use of alternating directions of multipliers method (ADMM) to combine DIP and RED into a robust single-shot phase recovery process. The use of ADMM, which is based on the variable splitting approach, made it possible to plug and play different denoisers without the need of explicit differentiation. Experimental results show that the sparsity-promoting denoisers give better results over DIP in terms of phase signal-to-noise ratio (SNR). Considering the computational complexities, we conclude that the total variation denoiser is more appropriate for hologram reconstruction. [ABSTRACT FROM AUTHOR]