Holographic Research Articles

PEAKO and peakTree: tools for detecting and interpreting peaks in cloud radar Doppler spectra – capabilities and limitations

Abstract. Cloud radar Doppler spectra are of particular interest for investigating cloud microphysical processes, such as ice formation, riming and ice multiplication. When hydrometeor types within a cloud radar observation volume have different terminal fall velocities, they can produce individual Doppler spectrum peaks. The peaks of different particle types can overlap and be further broadened and blended by turbulence and other dynamical effects. If these (sub-)peaks can be separated, properties of the underlying hydrometeor populations can potentially be estimated, such as their fall velocity, number, size and to some extent their shape. However, this task is complex and dependent on the operation settings of the specific cloud radar, as well as atmospheric dynamics and hydrometeor characteristics. As a consequence, there is a need for adjustable tools that are able to detect peaks in cloud radar Doppler spectra to extract the valuable information contained in them. This paper presents the synergistic use of two algorithms used for analyzing the peaks in Doppler spectra: PEAKO and peakTree. PEAKO is a supervised machine learning tool that can be trained to obtain the optimal parameters for detecting peaks in Doppler spectra for specific cloud radar instrument settings. The learned parameters can then be applied by peakTree, which is used to detect, organize and interpret Doppler spectrum peaks. The application of the improved PEAKO–peakTree toolkit is demonstrated in two case studies. The interpretation is supported by forward-simulated cloud radar Doppler spectra by the Passive and Active Microwave TRAnsfer tool (PAMTRA), which are also used to explore the limitations of the algorithm toolkit posed by turbulence and the number of spectral averages chosen in the radar settings. From the PAMTRA simulations, we can conclude that a minimum number of n = 20–40 spectral averages is desirable for Doppler spectrum peak discrimination. Furthermore, small liquid peaks can only be reliably separated for eddy dissipation rate values up to approximately 0.0002 m2 s−3 in the simulation setup which we tested here. The first case study demonstrates that the methods work for different radar systems and settings by comparing the results for two cloud radar systems which were operated simultaneously at a site in Punta Arenas, Chile. Detected peaks which can be attributed to liquid droplets agree well between the two systems, as well as with an independent liquid-predicting neural network. The second case study compares PEAKO–peakTree-detected cloud radar Doppler spectrum peaks to in situ observations collected by a balloon-based holographic imager during a campaign in Ny-Ålesund, Svalbard. This case demonstrates the algorithm toolkit's ability to identify different hydrometeor types but also reveals its limitations posed by strong turbulence and a low n. Despite these challenges, the algorithm toolkit offers a powerful means of extracting comprehensive information from cloud radar observations. In the future, we envision PEAKO–peakTree applications on the one hand for interpreting cloud microphysics in case studies. The identification of liquid cloud peaks emerges as a valuable asset, e.g., in studies on cloud radiative effects, in seeder–feeder processes, or for tracing vertical air motions. Furthermore, the computation of the moments for each subpeak enables the tracking of hydrometeor populations and the observation of growth processes along fallstreaks. On the other hand, PEAKO–peakTree applications could be extended to statistical evaluations of longer data sets. Both algorithms are openly available on GitHub, offering accessibility for the scientific community.

Optically Transparent Complex-Amplitude Metasurface for Full-Space Manipulation of Frequency-Multiplexed Holographic Imaging.

Restricted by the physical properties of materials, most traditional metasurfaces (MSs) cannot achieve transparent stealth in the visible spectrum. Although some metasurfaces for holography have been designed, there is no standard method for evaluating the advancement of wavefront manipulation under different design algorithms. Here, a complex-amplitude metasurface with optical transparency (OT) and full-space manipulation is presented in the millimeterwave band. Through frequency multiplexing, two holographic images "HOLO" and "GRAM" with high quality are designed, achieving the signal-to-noise ratios of 14.6 and 14.4 dB, respectively. The 64 × 64 bilayered metasurface consists of glass and poly(ethylene terephthalate) (PET) substrates and three metallic mesh layers. By change of the opening size and oriented angle of split rings, phase and amplitude modulations are independently realized. Besides, a new method is provided to assess the superiority of the metasurface holography system for near-field energy regulation. The prototype was fabricated using micro-nano-technology and tested. Two holographic images were experimentally demonstrated and show good agreement with theoretical calculations and simulated results. With the advantages of OT and full-space complex-amplitude customization, the proposed metasurface holograms for frequency-multiplexed may find prospective application aspects in target perception, multichannel data storage and encryption, and many other related fields.

Segment and Support: a dual-purpose Deep Learning solution for Limited Angle Holographic Tomography

Segment and Support: a dual-purpose Deep Learning solution for Limited Angle Holographic Tomography

HoloLume: Point-of-Application Holographic Imaging Solution

Abstract Digital holographic imaging has emerged as a label-free, non-invasive, and powerful tool, offering a transformative method for the real-time investigation of morphology, density, and other physical and mechanical features of biological and non-biological samples. The rapid development of these portable, economical imaging systems for clinical/non-clinical setups, especially in remote areas, is of great interest. These systems are early point-of-care applications in diagnosis, research, education, and training. This article reports a general-purpose, fully automated portable imaging tool, "HoloLume," that offers high-resolution 3D imaging that facilitates the comprehensive understanding and analysis of different biological/non-biological samples. The proposed microscopic system HoloLume realizes the interferogram generation of samples using common-path optics configuration with Fresnel biprism, and its motorized stage precisely scans the whole sample with a step of 3.87 μm for quick identification of the region of interest, which makes sure a time-efficient and robust analysis. The prototype, assembled from off-the-shelf components, costs approximately USD 1700 and weighs around 3 kg. To validate and verify the performance of the HoloLume microscope, we have conducted experiments on both non-biological and biological samples. Thus, its non-invasive nature, high temporal stability, and economical lightweight prototyping make it an ideal choice for hands-on learning and quantitative analysis, reducing the need for time-consuming sample preparation and conventionally expensive microscopic systems. Furthermore, the adaptability of the proposed imaging tool to remote environments ensures wider accessibility and its easy integration with other imaging modalities enables the user to gain insight into advanced research and diagnostics.

On the label-free analysis of white blood cells by holographic quantitative phase imaging flow cytometry

On the label-free analysis of white blood cells by holographic quantitative phase imaging flow cytometry

The Latest Development of Synthetic Aperture Radar: An Overview

Abstract. Synthetic Aperture Radar (SAR) technology enables high-resolution imaging regardless of weather conditions, offering immense potential for target detection and recognition. This paper reviews the latest advancements in SAR technology, highlighting key developments and applications. The limitations of traditional SAR imaging techniques, particularly the trade-off between resolution and swath width, have been addressed by High Resolution Wide Swath (HRWS) SAR, enabling simultaneous acquisition of high-resolution and wide-swath data. Multi-polarimetric SAR provides richer scattering information for improved target recognition accuracy, while deep learning algorithms enhance image quality and recognition performance. Emerging technologies like 3D-ISAR and holographic imaging offer novel approaches to target recognition and tracking. We discuss the development history, performance advantages, and limitations of these technologies, providing a comprehensive overview of their practical applications. We identify current challenges and future trends in SAR target imaging and recognition, including computational efficiency, adversarial attack defense, data acquisition and processing, and feature extraction and classification. Potential research directions, such as integrated multi-mode SAR systems, multi-source data fusion, and adversarial attack defense strategies, are outlined to fully harness the potential of SAR technology in target imaging and recognition.

Microcavity-assisted multi-resonant metasurfaces enabling versatile wavefront engineering

Metasurfaces have exhibited exceptional proficiency in precisely modulating light properties within narrow wavelength spectra. However, there is a growing demand for multi-resonant metasurfaces capable of wavefront engineering across broad spectral ranges. In this study, we introduce a microcavity-assisted multi-resonant metasurface platform that integrates subwavelength meta-atoms with a specially designed distributed Bragg reflector (DBR) substrate. This platform enables the simultaneous excitation of various resonant modes within the metasurface, resulting in multiple high-Q resonances spanning from the visible to the near-infrared (NIR) regions. The developed metasurface generates up to 15 high-Q resonant peaks across the visible-NIR spectrum, achieving a maximum efficiency of 81% (70.7%) in simulation (experiment) with an average efficiency of 76.6% (54.5%) and a standard deviation of 4.1% (11.1%). Additionally, we demonstrate the versatility of the multi-resonant metasurface in amplitude, phase, and wavefront modulations at peak wavelengths. By integrating structural color printing and vectorial holographic imaging, our proposed metasurface platform shows potential for applications in optical displays and encryption. This work paves the way for the development of next-generation multi-resonant metasurfaces with broad-ranging applications in photonics and beyond.

Ultrafast imaging of laser-induced modifications in planar targets via single-shot in-line holography

Abstract We present a holographic single-shot coherent diffractive imaging method based on in-line holography that allows the ultrafast characterization of 2D transmission maps of semi-transparent planar targets such as foils in amplitude and phase. Holographic information is obtained from the interference of the transmitted primary beam with the fields scattered from the modified or unknown target regions. A specialized iterative phase retrieval is used to incorporate the holographic nature of the approach and to accelerate and improve convergence. The achievable quality and reproducibility of the reconstructed transmission maps as well as optimal setup parameters are investigated using realistic pre-characterized reference targets. We used non-circular laser-induced hole structures in 30 nm thin gold foils that represent the final state of a laser modification and show that the far field error of the reconstructed diffraction images can be used to estimate and optimize the reconstruction quality in the object plane in order to obtain accurate and reproducible transmission maps. Our results mark the important first step towards the full spatio-temporal analysis of all stages of laser material modification or laser ablation in two-color pump probe experiments, including

Holographic Communication: A Study of the Quality of Holographic Copies Perception

Relevance. Holography is becoming one of the most promising areas of visualization of three-dimensional objects, which justifies the emergence of a certain scientific interest in this area of research. There is a general global trend of intensifying the work of specialists on the problem of using holographic technologies in various areas of human activity. Trends in the implementation of holographic services and holographic communication today already require a revision of the principles of planning, designing and building existing communication networks, as well as approaches to the implementation of sixth-generation networks 6G, which are based on the integration of various technologies and communication networks into a single network. A separate issue is the assessment of the quality of service and the quality of perception of holographic services by both objective and subjective assessment methods. There are practically no criteria for assessing the quality of a holographic image, including scales and methods for subjective assessment of the quality of holographic services. Moreover, the properties of the holographic flow are poorly understood, and even less so its influence on communication networks and requirements for network parameters, which makes the tasks of studying traffic characteristics and assessing the quality of service of holographic services very relevant.The aim of the work is to evaluate the quality of perception of holographic conference calls using a subjective evaluation method on a model network. The work uses methods of subjective assessment of the quality of perception. The materials presented in the article reflect the results of the authors' experimental research work on studying the problem of the quality of perception of holographic copies. A description of the developed scheme of a full-scale experiment is given.Results. The data obtained as a result of the work of an expert group on assessing the quality of perception are presented. The subjective assessment of the quality of perception of a holographic image begins to deteriorate with 8 connections and becomes unsatisfactory with 12 connections, which must be taken into account when planning experimental studies of work on assessing the quality of perception. Novelty. For the first time, an assessment of the quality of perception of the provision of a holographic conferencing service was carried out using a subjective assessment method. Theoretical significance. The influence of increasing the number of holographic traffic flows on the quality of perception of the received content is analyzed. Practical significance. Expanding the possibilities for assessing the degree of user satisfaction with holographic services.

Π-shaped pixel pattern for shift multiplexing surface holograms in holographic data storage

In this study, a method for shift multiplexing surface holograms was proposed for data storage systems. Shift multiplexing of surface holograms is inhibited by noise specific to Raman–Nath diffraction. We proposed a model to analyze the influence of noise. Subsequently, we proposed a method for noise suppression to arrange signal and reference pixels in a shape similar to the Greek letter “Π.” The proposed method is generally applicable to thin holograms in which Raman–Nath diffraction occurs. The effectiveness of noise suppression using the proposed method was experimentally demonstrated. We theoretically estimated that a shift multiplexing surface holographic data storage system using the proposed method could achieve a significantly higher data transfer rate than conventional optical discs while maintaining a comparable storage density.

Bi-functional and tri-channel image displays based on a single-size nanostructured metasurface enabled by dual-orientation-degeneracy

Benefiting from the extraordinary ability of manipulating lightwaves at the subwavelength scale, nanostructured metasurfaces are expected to achieve multifunctional and multichannel integration to expand functionality and increase information capacity. However, multifunctional and multichannel metasurfaces always consist of various anisotropic nanostructures, inevitably bringing challenges to design and fabrication. In this study, we propose a concept of dual-orientation-degeneracy containing twofold orientation degeneracy. The first-level degeneracy is a one-to-four mapping scheme between the intensity of Channel 1 and orientation angle and the second-level degeneracy refers to a one-to-two mapping between the intensity of Channel 2 and orientation angle. Additionally, we provide a minimalist design of bi-functional and tri-channel image displays based on a single-size nanostructured metasurface. The designed metasurface integrates two functionalities of nanoprinting and holography, which can generate a continuous grayscale meta-image, a binary meta-image and a phase-only holographic image. Three channel displays can be readily switched by polarization controls. More importantly, the metasurface is achieved merely by reconfiguring the orientation angles of the nanostructures with fixed geometries, relieving the structure design and fabrication burden. The presented minimalist design strategy is universal and applicable, which can contribute to advanced research and applications in ultra-compact image displays, high-dense optical storage, multi-folded optical anti-counterfeiting, etc.

An integrated portable system for laser speckle contrast imaging and digital holographic microscopy

A multimodal quantitative phase imaging platform combining digital holographic microscopy (DHM) with laser speckle contrast imaging (LSCI) is demonstrated for imaging weakly scattering and transparent samples in a label-free manner. It uses the principle of coherence of the light source for interferometric detection of phase of transparent and semi-transparent samples. The speckle formation resulting from the coherence property of the laser source is used to track dynamic activities in the regions of interest in the sample. Integration of these two techniques onto a microfluidic chip leads to an optofluidic real-time microscope for live cell imaging applications. In this work, we have developed an integrated multimodal system combining digital holographic microscopy and laser speckle contrast imaging system for Optofluidics and in vitro studies. The sample flowing through the microfluidic channel is imaged to record holograms and video of intensity images at the same time. This enables to map the flow within a microfluidic channel and quantify the channel as well as the particle flow through the channel. The channel morphology along with the particles flowing through the channel are quantified using DHM. The two-dimensional speckle contrast images map the flow of the dynamic microbeads and cells with very high contrast in almost real time. A low-cost portable multimodal quantitative phase microscope combining DHM and LSCI has been demonstrated for real time imaging with applications in optofluidics.

3D digital holography for measuring particle impact crater morphology and in-situ analysis of oxidation healing on steel surfaces

Deformation and erosion of steel due to particle impacts in high-temperature environments are common issues in industrial applications. Under high-temperature conditions, an oxide layer forms that affects the deformation and erosion of the steel surface following particle impacts. Studying the interaction mechanism of oxidation and deformation (erosion) is of considerable significance. Traditional research methods primarily involve ex-situ measurements on samples post-erosion and oxidation, which cannot capture the morphological changes of the steel surface immediately following particle impact. Utilizing 3D digital holography (DH) technology, this paper develops a measurement system to investigate the surface morphological changes in steel induced by single particle impacts. We utilized this experimental system to measure the impact crater morphology of 500 μm zirconia particles impacting Q690 steel sheets. Our findings indicate that Hertzian ring cracks formation is significantly affected by heating temperature and impact angle. Notably, oxide layer peeling and erosion occurred at an impact angle of 30°. Additionally, impact crater depths at a 90° angle and impact speeds ranging from 1 to 20 m/s varied between 0.66 and 4.25 μm, with crater depths showing a correlation to the thickness of the oxide layer. Concurrently, in-situ measurements of the impact crater healing process during heating revealed that the crater formed at a 30° impact angle, which had numerous microcracks, exhibited significantly better healing compared to the crater formed at a 90° impact angle. The thickening process of the oxide layer were also analyzed, leading to the derivation of the oxide layer growth kinetic equation based on the measurement data: . This study is the first to use DH technology to measure the surface morphology of steel and to conduct in-situ analysis of the oxide layer thickening process following particle impact and during heating. This approach provides a novel perspective for understanding the erosion-oxidation interaction mechanism.

Integration of Augmented Reality in Temporal Bone and Skull Base Surgeries.

Augmented reality technologies provide transformative solutions in various surgical fields. Our research focuses on the use of an advanced augmented reality system that projects 3D holographic images directly into surgical footage, potentially improving the surgeon's orientation to the surgical field and lowering the cognitive load. We created a novel system that combines exoscopic surgical footage from the "ORBEYE" and displays both the surgical field and 3D holograms on a single screen. This setup enables surgeons to use the system without using head-mounted displays, instead viewing the integrated images on a 3D monitor. Thirteen surgeons and surgical assistants completed tasks with 2D and 3D graphical surgical guides. The NASA Task Load Index was used to assess mental, physical, and temporal demands. The use of 3D graphical surgical guides significantly improved performance metrics in cochlear implant surgeries by lowering mental, physical, temporal, and frustration levels. However, for Bonebridge implantation, the 2D graphical surgical guide performed better overall (p = 0.045). Participants found the augmented reality system's video latency to be imperceptible, measuring 0.13 ± 0.01 s. This advanced augmented reality system significantly improves the efficiency and precision of cochlear implant surgeries by lowering cognitive load and improving spatial orientation.

Multifunctional computational fluorescence self-interference holographic microscopy

Fluorescence microscopy is crucial in various fields such as biology, medicine, and life sciences. Fluorescence self-interference holographic microscopy has great potential in bio-imaging owing to its unique wavefront coding characteristics; thus, it can be employed as three-dimensional (3D) scanning-free super-resolution microscopy. However, the available approaches are limited to low optical efficiency, complex optical setups, and single imaging functions. The geometric phase lens can efficiently manipulate the optical field’s amplitude, phase, and polarization. Inspired by geometric phase and self-interference holography, a self-interference fluorescent holographic microscope-based geometric phase lens is proposed. This system allows for wide-field, 3D fluorescence holographic imaging, and edge-enhancement from the reconstruction of only one complex-valued hologram. Experiments demonstrate the effectiveness of our method in imaging biological samples, with improved resolution and signal-to-noise ratio. Furthermore, its simplicity and convenience make it easily compatible with existing optical microscope setups, making it a powerful tool for observing biological samples and detecting industrial defects.

Flexible Control of Encoded Metasurface Holographic Imaging Based on Fourier Convolution Principle

Flexible Control of Encoded Metasurface Holographic Imaging Based on Fourier Convolution Principle

Point spread function engineering enable resolution enhanced imaging for Interferenceless coded aperture correlation holography

The point spread function (PSF) of an optical system could characterize the resolving ability of the whole optical system for point light sources. Therefore, the imaging performance of the system could be significantly improved by regulating and optimizing the PSF. In this paper, we innovatively propose a single-exposure hologram resolution enhanced cross-correlation (RECC) method for Interferenceless coded aperture holography(I-COACH) system, circumventing the necessity to obtain the point spread hologram (PSH) of an ideal point object. The RECC method firstly acquires an approximate image of a large-size point object by Lucy-Richardson (LR) algorithm in lens imaging mode, and takes it as a PSF to acquire a PSH with ideal size of the I-COACH system by LR algorithm again, and finally acquires a reconstructed image by the single-exposure hologram RECC method. In the RECC method, the approximate ideal PSHs at different axial positions of the system are acquired by offline operation, therefore, it has a high imaging temporal resolution, and the imaging transverse resolution is not affected by the size of the point objects at the time of recording the PSH, which provides a high imaging signal-to-noise ratio and stable resolution. The proposed method provides powerful technical support for further extending the application field of the I-COACH system, and provides technical reference for other incoherent imaging.

3D Multiview Holographic Display with Wide Field of View Based on Metasurface

Abstract3D display technology offers a more realistic visual experience by allowing users to perceive depth and spatial awareness, enhancing interactivity and immersion. Among various approaches, multiview display technology constructs 3D images by offering multiple smooth views along the horizontal plane. Metasurfaces, with ultra‐thin physical structures and flexible functional designs, are positioned to make significant contributions to the evolution of 3D display technologies. Here, a 3D multiview holographic display system based on metasurfaces is proposed. Using generalized Snell's law, a spatially multiplexed metasurface is designed with nine views and achieves 3D display by cascading the metasurface with a spatial light modulator (SLM). By projecting holograms onto different areas of the metasurface via the SLM, corresponding reconstructed images can be observed from specific designed directions. Thanks to the large numerical aperture (NA) of the metasurface, the system successfully achieves nine views within a 120° field of view (FOV, with a theoretical maximum of 180°), validated experimentally. This system promises potential applications in VR/AR display, surgical navigation, geographic information system (GIS), and other fields.

Three-dimensional computer holography with phase space tailoring

Computer holography is a prominent technique for reconstructing customized three-dimensional (3D) diffraction fields. However, the quality of optical reconstruction remains a fundamental challenge in 3D computer holography, especially for the 3D diffraction fields with physically continuous and extensive depth range. Here, we propose a 3D computer-generated hologram (CGH) optimization framework with phase space tailoring. Based on phase space analysis of the space and frequency properties in both lateral and axial directions, the intensity of the 3D diffraction field is adequately sampled across a large depth range. This sampling ensures the reconstructed intensity distribution to be comprehensively constrained with physical consistency. A physics-informed loss function is constructed based on the phase space tailoring to optimize the CGH with suppression of vortex stagnation. Numerical and optical experiments demonstrate the proposed method significantly enhances the 3D optical reconstructions with suppressed speckle noise across a continuous and extensive depth range.

High-resolution transcranial optical imaging of in vivo neural activity

Rapid sub-nanometer neuronal deformations have been shown to occur as a consequence of action potentials in vitro, allowing for optical registration of discrete axonal and synaptic depolarizations. Such optically-measured deformations are a novel signature for recording neural activity. We demonstrate this signature can be extended to in vivo measurements through recording of rapid neuronal deformations on the population level with holographic, optical phase-based recordings. Our system demonstrates, for the first time, non-invasive recordings of in vivo tissue deformation associated with population level neuronal activity, including through-skull. We confirmed this technique across a range of neural activation models, including direct epidural focal electrical stimulation, anesthetic-induced cortical deactivation, activation of primary somatosensory cortex via whisker barrel stimulation, and pharmacologically-induced seizures. Collectively, we show holographic imaging provides a pathway for high-resolution, label-free, non-invasive recording of transcranial in vivo neural activity at depth, making it highly advantageous for studying neural function and signaling.