Holographic Applications Research Articles

Editorial: Advances in digital holographic microscopy and applications

Editorial: Advances in digital holographic microscopy and applications

Single-pixel deep phase-shifting incoherent digital holography

Incoherent digital holography technology reduces the requirement for coherence of light sources, greatly expanding the application range of digital holography. In this paper, we designed a Multi-head attention single-pixel (MHASP) phase-shifting network for incoherent digital holography. The trained network has the capability to effortlessly predict three interferograms, encompassing phase shifts of 0, 2/3 π, and 4/3 π, solely from one-dimensional input data. Utilizing the conventional three-step phase-shifting method, we are able to effectively eliminate the DC and twin terms from the holographic reconstruction process, subsequently achieving a high-fidelity reconstruction facilitated by the employment of the back propagation algorithm. The comprehensive experimental findings clearly indicate that, beyond facilitating high-precision reconstruction, the introduced MHASP phase-shifting approach efficiently preserves 3D information through calibrating the back propagation distance, even when confronted with a reduced volume of holographic data. Furthermore, the introduced approach uses a network to replace the actual phase shift operation, which can better improve the utilization of object light energy. This approach not only circumvented the constraints posed by area array sensors but also facilitated high-fidelity imaging with minimal data volume, thereby expanding the horizons of incoherent digital holography applications in the realm of 3D imaging.

Rapid terahertz beam profiling and antenna characterization with phase-shifting holography

In this paper we investigate the application of phase-shifting digital holography for the real-time characterization of electromagnetic sources in the THz frequency range. We use an off-the-shelf terahertz detector array composed of 64×64\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$64 \ imes 64$$\\end{document} power-sensitive pixels, over an area of 96mm×96mm\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$96\\,\\hbox {mm} \ imes 96\\,\\hbox {mm}$$\\end{document}, to record intensity interferograms cast between the coherent radiation emitted from a reference source and an unknown antenna under test. This approach parallelizes the acquisition process with respect to conventional near-field point scanning methods, reducing the measurement time by orders of magnitude. In our system, the measurement time is limited only by the refresh rate of the detector array and the speed of a delay line stage that is used to phase-shift the reference wave. As a proof-of-principle demonstration, we map the 2D near-field distribution and estimate the far-field radiation pattern emitted by a plano-convex PTFE spherical lens antenna illuminated by a diagonal horn at 290 GHz frequency with ∼1Hz\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sim \\,1\\,\\hbox {Hz}$$\\end{document} refresh rate.

Three-Dimensional Quantum Black Holes: A Primer

We review constructions of three-dimensional ‘quantum’ black holes. Such spacetimes arise via holographic braneworlds and are exact solutions to an induced higher-derivative theory of gravity consistently coupled to a large-c quantum field theory with an ultraviolet cutoff, accounting for all orders of semi-classical backreaction. Notably, such quantum-corrected black holes are much larger than the Planck length. We describe the geometry and horizon thermodynamics of a host of asymptotically (anti-) de Sitter and flat quantum black holes. A summary of higher-dimensional extensions is given. We survey multiple applications of quantum black holes and braneworld holography.

Speckle reduction in digital holography with Non-local means filter based on the structural similarity

Speckle noise limits the application of digital holography across various fields. This paper proposes a Non-local means filter method to suppress speckle noise by determining the weight of each traversed pixel based on the structural similarity between image blocks centered on the target and traversed pixels. Experimental results show that, compared to other typical digital image processing methods, this method can significantly reduce the speckle noise and exhibits a clear advantage across various metrics. These results indicate that the proposed method holds significant development potential in the field of speckle noise reduction.

ConIQA: A deep learning method for perceptual image quality assessment with limited data

Effectively assessing the realism and naturalness of images in virtual (VR) and augmented (AR) reality applications requires Full Reference Image Quality Assessment (FR-IQA) metrics that closely align with human perception. Deep learning-based IQAs that are trained on human-labeled data have recently shown promise in generic computer vision tasks. However, their performance decreases in applications where perfect matches between the reference and the distorted images should not be expected, or whenever distortion patterns are restricted to specific domains. Tackling this issue necessitates training a task-specific neural network, yet generating human-labeled FR-IQAs is costly, and deep learning typically demands substantial labeled data. To address these challenges, we developed ConIQA, a deep learning-based IQA that leverages consistency training and a novel data augmentation method to learn from both labeled and unlabeled data. This makes ConIQA well-suited for contexts with scarce labeled data. To validate ConIQA, we considered the example application of Computer-Generated Holography (CGH) where specific artifacts such as ringing, speckle, and quantization errors routinely occur, yet are not explicitly accounted for by existing IQAs. We developed a new dataset, HQA1k, that comprises 1000 natural images each paired with an image rendered using various popular CGH algorithms, and quality-rated by thirteen human participants. Our results show that ConIQA achieves superior Pearson (0.98), Spearman (0.965), and Kendall’s tau (0.86) correlations over fifteen FR-IQA metrics by up to 5%, showcasing significant improvements in aligning with human perception on the HQA1k dataset.

Method for fabricating circular polarization beam splitters based on polarization holography.

Based on polarization holography, circular polarization beam splitters with separation angles of up to 100° have been fabricated. The left- and right-handed circularly polarized waves can be reconstructed by the two holograms that were designed by the tensor theory of polarization holography, respectively. In the fabrication of circular polarization beam splitters, two holograms were recorded only by the interference method in the same area of the polarization-sensitive material. This method is simple, inexpensive, and easy to adjust the separation angles and element size. The diffraction efficiency and the polarization state of the reconstructed waves were tested under different incident waves, and the experimental results are in good agreement with the theory. This work not only deepens our understanding of polarization holography but also expands the applications of polarization holography.

High Refractive Index, Low Birefringence Holographic Materials via the Homopolymerization of 1,2-Dithiolanes.

High refractive index, low birefringence photopolymers were created via the radical-mediated, ring opening homopolymerization of 1,2-dithiolane functionalized monomers and were subsequently evaluated as holographic recording media. This investigation systematically characterized the reaction kinetics, thermodynamics, and volume shrinkage of the 1,2-dithiolane homopolymerization as well as the optical transparency, refractive index, birefringence, and holographic performance of multifunctional 1,2-dithiolane functionalized monomers and their resultant polymers. Real-time kinetic and thermodynamic analyses of a monofunctional 1,2-dithiolane monomer, lipoic acid methyl ester (LipOMe), indicated rapid monomer conversion, exceeding 90% in 60 s, with an overall enthalpy of reaction of 18 ± 1 kJ/mol. The ring-opening polymerization resulted in low shrinkage (10.6 ± 0.3 cm3/mol dithiolane) and a significant bulk refractive index increase (0.030 ± 0.003). The resulting photopolymers exhibited high optical transparency, minimal haze, and negligible birefringence, suggesting the potential of 1,2-homopolymers as optical materials. To further explore the specific capabilities for use as high-performance holographic recording applications, several multifunctional monomers were synthesized with the ethanedithiol lipoic acid monomer (EDT-Lip2) selected for experimentation. Holographic diffraction gratings written using this monomer achieved a peak-to-mean refractive index modulation of 0.008 with minimal haze and birefringence.

Carrollian supersymmetry and SYK-like models

This work challenges the conventional notion that in a spacetime dimension higher than one, a supersymmetric Lagrangian invariably consists of purely bosonic terms, purely fermionic terms, as well as boson-fermion mixing terms. By recasting a relativistic Lagrangian in terms of its nonrelativistic and ultrarelativistic sectors, we reveal that an ultrarelativistic (Carrollian) supersymmetric Lagrangian exhibits an exotic feature; that is, it can exist without a purely bosonic contribution. Based on this result, we demonstrate a link between higher-dimensional Carrollian and (0+1)-dimensional quantum mechanical models, yielding higher-order extensions of supersymmetric Sachdev-Ye-Kitaev (SYK) models in which purely bosonic higher-order terms are absent. Given that supersymmetry plays an essential role in improving the quantum behavior and solubility, our findings may lead to interesting applications in non-AdS holography. Published by the American Physical Society 2024

Adaptive phase control of a phase-only spatial light modulator using the Shack-Hartmann wavefront sensor

We present a method to study both static and dynamic phase errors in a phase-only spatial light modulator (SLM) caused by surface irregularities and an imperfect response of each pixel to the applied field. This, in turn, degrades optical reconstruction, particularly in holographic projection applications. The approach uses the Shack-Hartmann wavefront sensor (SHWFS) to measure these errors. A plane wave illuminates the SLM, and the reflected wavefront is measured by the SHWFS and converted into a phase-only computer-generated hologram (CGH). This CGH is displayed on the SLM to compensate for phase errors, which are verified by subsequent wavefront measurements. Experimental results demonstrate the simplicity, robustness to vibration, and real-time capabilities of the SHWFS in contrast to interferometric methods.

Holographic Applications in STEM Pedagogy and Training

Holographic Applications in STEM Pedagogy and Training

Engineered 3D Vortex Array with Customized Energy and Topological Charges for Multi‐View Display

AbstractArrays of multiple vortex beams enhance parallel processing capabilities from particle manipulation to information communication. However, the spatial position, topological charge, and energy parameters of the vortex beams within the array have yet to be precisely controlled, posing significant challenges to the realization of multi‐view 3D Orbital Angular Momentum (OAM) display using vortex arrays as information carriers. To address this issue, a method for generating vortex arrays based on a phase‐only hologram, customizing the array by using the energy and OAM spectrum of each vortex beam as the loss function is developed. Experimental results indicate that a 2D array generates 100 vortex beams in the spatial frequency domain, while a 3D array in the Fresnel zone produces 252 vortex beams across 7 planes, each with 36 unprecedentedly controllable energy and topological charge vortex beams. Subsequently, images of 4 views using the 3D vortex arrays and decoded through coordinate transformation to achieve a multi‐view 3D OAM display are encoded. The results demonstrate imaging quality with Mean Peak Signal‐to‐Noise Ratio (MPSNR) of 12.7, 13.0, 13.4, and 12.2 dB in 4 views, respectively, offering promising opportunities for applications in 3D optical manipulation, high‐capacity communication, and 3D OAM holography.

High-resolution imaging for in-situ non-destructive testing by quantitative lensless digital holography

Quantitative imaging technologies for in-situ non-destructive testing (NDT) demand high-resolution, wide-field, and stable metrology capabilities. Moreover, live processing and automation are vital for real-time quality control and inspection. Conventional methods use complex optical setups, resulting in large, immobile systems which can solely operate within controlled environmental conditions due to temporal instabilities, rendering them unsuitable for in-situ measurements of micro-to nano-scale physical phenomena. This article delves into the multiphysics application of lensless digital holography, emphasizing its metrological capacity for various in-situ scenarios, while acknowledging and characterizing the differing constraints imposed by various physical phenomena, both transient and steady-state. The digital reconstruction of holograms is computed in real-time, and numerical focusing capabilities allow for instantaneous retrieval of the optical phase at various working distances without the need of complex optical setups, making lensless digital holography well-suited for in-situ quantitative imaging under various types of environments. Current NDT capabilities are demonstrated, including high-resolution and real-time reconstructions, simultaneous measurements for comparative metrology, and practical applications ranging from vibrations and acoustics to thermo-mechanics. Furthermore, methodologies to enhance overall metrology capabilities are exploited, addressing the study of existing physical phenomena, thereby expanding the applicability of holographic techniques across diverse industrial sectors.

Strong-field photoelectron holography in the subcycle limit

Strong-field photoelectron holography is promising for the study of electron dynamics and structure in atoms and molecules, with superior spatiotemporal resolution compared to conventional electron and X-ray diffractometry. However, the application of strong-field photoelectron holography has been hindered by inter-cycle interference from multicycle fields. Here, we address this challenge by employing a near-single-cycle field to suppress the inter-cycle interference. We observed and separated two distinct holographic patterns for the first time. Our measurements allow us not only to identify the Gouy phase effect on electron wavepackets and holographic patterns but also to correctly extract the internuclear separation of the target molecule from the holographic pattern. Our work leads to a leap jump from theory to application in the field of strong-field photoelectron holography-based ultrafast imaging of molecular structures.

Application of deep learning and inline holography to estimate the droplet size distribution

We examine five machine learning-based architectures to estimate the droplet size distributions obtained using digital inline holography. The architectures, namely, U-Net, R2 U-Net, Attention U-Net, V-Net, and Residual U-Net, are trained using synthetic holographic images. Our assessment focuses on evaluating the training, validation, and prediction performance of these architectures. Our results indicate that U-Net and R2 U-Net are the most proficient architectures, consistently demonstrating superior performance trends and achieving the highest Intersection Over Union (IOU) scores among the five architectures studied. We employ additional training using experimental holographic images for the two top-performing architectures to validate their efficacy further. Subsequently, they are employed to segment an experimental dataset illustrating the bag breakup phenomenon, facilitating the extraction of size distribution. The extracted size distribution from U-Net and R2 U-Net segmentation is then compared with the analytical model proposed by Jackiw and Ashgriz (2022) by employing the gamma and log-normal distributions. Our findings indicate that the gamma distribution provides a more accurate prediction of the multi-modal size distribution than the log-normal distribution owing to its long exponential tail. The present study offers valuable insights into the effectiveness of machine learning architectures in estimating particle/droplet sizes, highlighting their practical application in real-world experimental scenarios.

Removal of algorithmic stagnation by augmented iterative phase retrieval

Retrieving the phase of an optical field using intensity measurements is one of the most widespread and studied inverse problems in classical optics. However, common iterative approaches such as the Gerchberg-Saxton algorithm and its derivatives suffer from the twin-image problem – the iterative minimisation stagnates and the recovered field contains features from both the target field and its point-reflection. We present a technique that leverages mathematical properties of the stagnated field, to constrain the problem and remove the twin image artefacts. This improvement in reconstruction robustness has implications in a range of fields, including applications in adaptive optics, holography and optical communications.

Digital Holography and 3D Imaging 2023: introduction to the joint feature issue in Applied Optics and Journal of the Optical Society of America A.

The Optica Topical Meeting on Digital Holography and 3D Imaging (DH) was held 14-17 August 2023 in Boston, Massachusetts. The meeting was organized co-jointly with the Optica Imaging Congress. Feature issues based on the DH meeting series have been released by Applied Optics (AO) since 2007. Since 2017, AO and the Journal of the Optical Society of America A (JOSA A) have presented a feature issue in each journal. This feature issues includes 17 papers in AO and 9 in JOSA A. Together they cover a large range of topics, reflecting the rapidly expanding techniques and applications of digital holography and 3D imaging. The upcoming DH Conference (DH 2024) will be held from 3 to 6 June in Paestum, Italy.

Digital Holography and 3D Imaging: introduction to the joint feature issue in Applied Optics and Journal of the Optical Society of America A.

The Optica Topical Meeting on Digital Holography and 3D Imaging (DH) was held 14-17 August 2023 in Boston, Massachusetts. The meeting was organized co-jointly with the Optica Imaging Congress. Feature issues based on the DH meeting series have been released by Applied Optics (AO) since 2007. Since 2017, AO and the Journal of the Optical Society of America A (JOSA A) have presented a feature issue in each journal. This feature issues includes 17 papers in AO and 9 in JOSA A. Together they cover a large range of topics, reflecting the rapidly expanding techniques and applications of digital holography and 3D imaging. The upcoming DH Conference (DH 2024) will be held from 3 to 6 June in Paestum, Italy.

Large Field-of-View Nonlinear Holography in Lithium Niobate.

A nonlinear holographic technique is capable of processing optical information in the newly generated optical frequencies, enabling fascinating functions in laser display, security storage, and image recognition. One popular nonlinear hologram is based on a periodically poled lithium niobate (LN) crystal. However, due to the limitations of traditional fabrication techniques, the pixel size of the LN hologram is typically several micrometers, resulting in a limited field-of-voew (FOV) of several degrees. Here, we experimentally demonstrate an ultra-high-resolution LN hologram by using the laser poling technique. The minimal pixel size reaches 200 nm, and the FOV is extended above 120° in our experiments. The image distortions at large view angles are effectively suppressed through the Fourier transform. The FOV is further improved by combining multiple diffraction orders of SH fields. The ultimate FOV under our configuration is decided by a Fresnel transmission. Our results pave the way for expanding the applications of nonlinear holography to wide-view imaging and display.

Accelerated generation of holograms with ultra-low memory symmetrically high-compressed look-up table

Computer-generated holography technology has been widely applied, and as research in this field deepens, the demand for memory and computational power in small AR and VR devices continues to increase. This paper presents a hologram generation method, i.e., a symmetrically high-compressed look-up table method, which can reduce memory usage by 50%. In offline computing, half of the basic horizontal and vertical modulation factors are stored, halving the memory requirements without affecting inline speed. Currently, its potential extends to various holographic applications, including the production of optical diffraction elements.