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We introduce the holographic air‐quality monitor (HAM) system, uniquely tailored for monitoring large particulate matter (PM) over 10 μm in diameter—particles critical for disease transmission and public health but overlooked by most commercial PM sensors. The HAM system utilizes a lensless digital inline holography (DIH) sensor combined with a deep learning model, enabling real‐time detection of PMs with greater than 97% true positive rate at less than 0.6% false positive rate and analysis of PMs by size and morphology at a sampling rate of 26 L/min for a wide range of particle concentrations up to 4000 particles/L. Such throughput not only significantly outperforms traditional imaging‐based sensors but also rivals some lower‐fidelity, nonimaging sensors. Additionally, the HAM system is equipped with additional sensors for smaller PMs and various air quality conditions, ensuring a comprehensive assessment of indoor air quality. The performance of the DIH sensor within the HAM system was evaluated through comparison with brightfield microscopy, showing high concordance in size and morphology measurements. The efficacy of the DIH sensor was also demonstrated in two 2‐h experiments under different environments simulating practical conditions, with one involving distinct PM‐generating events. These tests highlighted the HAM system's advanced capability to differentiate PM events from background noise and its exceptional sensitivity to irregular, large‐sized PMs of low concentration. [ABSTRACT FROM AUTHOR]

Background: Esophageal cancer management lacks reliable response predictors to chemotherapy. In this study we evaluated the feasibility and accuracy of Biodynamic Imaging (BDI), a technology that employs digital holography as a rapid predictor of chemotherapy sensitivity in locoregional esophageal adenocarcinoma. Methods: Pre-treatment endoscopic pinch biopsies were collected from patients with esophageal adenocarcinoma during standard staging procedures. BDI analyzed the tumor samples and assessed in vitro chemotherapy sensitivity. BDI sensitivity predictions were compared to patients' pathological responses, the gold standard for determining clinical response, in the surgically treated subset (n=18). Result: BDI was feasible with timely tissue acquisition, collection, and processing in all 30 enrolled patients and successful BDI analysis in 28/29 (96%) eligible. BDI accurately predicted chemotherapy response in 13/18 (72.2%) patients using a classifier for complete, marked, and partial/no-response. BDI technology had 100% negative predictive value for complete pathological response hence identifying patients unlikely to respond to treatment. Conclusion: BDI technology can potentially predict patients' response to platinum chemotherapy. Additionally, this technology represents a promising step towards optimizing treatment strategies for esophageal adenocarcinoma patients by pre-emptively identifying non-responders to conventional platinumbased chemotherapy. [ABSTRACT FROM AUTHOR]

Digital holography is actively used for the characterization of objects and 3D-scenes, tracking changes in medium parameters, 3D shape reconstruction, detection of micro-object positions, etc. To obtain high-quality images of objects, it is often necessary to register a set of holograms or to select a noise suppression method for specific experimental conditions. In this paper, we propose a method to improve filtering in digital holography. The method requires a single hologram only. It utilizes interpolation upscaling of the reconstructed image size, filtering (e.g., median, BM3D, or NLM), and interpolation to the original image size. The method is validated on computer-generated and experimentally registered digital holograms. Interpolation methods coefficients and filter parameters were analyzed. The quality is improved in comparison with digital image filtering up to 1.4 times in speckle contrast on the registered holograms and up to 17% and 29% in SSIM and NSTD values on the computer-generated holograms. The proposed method is convenient in practice since its realization requires small changes of standard filters, improving the quality of the reconstructed image. [ABSTRACT FROM AUTHOR]

Digital holography has transformative potential for the measurement of stacked-chip microstructures due to its non-invasive, single-shot, full-field characteristics. However, significant light scattering and diffraction at steep edges in step microstructures cause the batwing effect, leading to measurement errors. Herein, we propose a standard-deviation-based adaptive median filter to eliminate batwing effects in step microstructure measurement using digital holography. The standard deviation determines the positions of the steps and the range of the batwing effect. During filtering, the filter window size varies: it adjusts according to the center's position within the batwing effect range and reduces outside this range to prevent distortion in other regions. Filtering weights are set to maintain information integrity while using larger filter windows. Experiments on the Standard Resolution Target USAF 1951 and the standard step height target show that our method successfully eliminates batwings while preserving the integrity of the remaining profile. [ABSTRACT FROM AUTHOR]

We explore the principles, implementation details, and performance characteristics of a lensless multi-spectral digital holographic sensor and demonstrate its potential for quality assurance in semiconductor manufacturing. The method is based on capturing multi-spectral digital holograms, which are subsequently utilized to evaluate the shape of a reflective test object. It allows for a compact setup satisfying high demands regarding robustness against mechanical vibrations and thus overcomes limitations associated with conventional optical inspection setups associated with lens-based white light interferometry. Additionally, the tunable laser source enhances the versatility of the system and enables adaptation to various sample characteristics. Experimental results based on a wafer test specimen demonstrate the effectiveness of the method. The axial resolution of the sensor is ± 2.5 nm, corresponding to 1σ. [ABSTRACT FROM AUTHOR]

Surface plasmon resonance (SPR) holographic microscopy exploits surface plasmon wave as illumination and acquires both SPR intensity and phase images. It detects extremely tiny variations of weakly interacting objects owing to high sensitivity and has been applied in cell biology, material science, surface chemistry, etc. However, it is very challenging to solve the problem of poor spatial resolution due to the transverse propagation of surface plasmon wave. In this paper, an azimuthal scanning excitation method is proposed in SPR holographic microscopy to improve the spatial resolution by engineering the Fourier spectra of SPR images from dual‐arc to circular shape. The study modulates the light field with spatial position, wavevector, and polarization to realize azimuthal scanning excitation of SPR. Systematic experiments of dielectric spheres, nanowires, two‐dimension materials, and complex nanostructure are conducted to show the resolution improvement with one order of magnitude, the higher detection sensitivity of SPR phase than that of SPR intensity, and the necessities of both of high‐resolution SPR intensity and phase images to retrieve sample information in certain scenarios. Benefiting from the high detection sensitivity and spatial resolution, the proposed microscopy will find wide applications in nanoparticle analysis, low‐dimensional material characterization, and imaging extremely thin or transparent samples. [ABSTRACT FROM AUTHOR]

The Jones matrix is a powerful quantitative tool for polarimetric imaging and characterization, where the matrix elements represent the intrinsic optical properties of the anisotropic objects on interaction with the polarized light. Most of the state‐of‐the‐art single‐shot Jones‐matrix imaging techniques rely on interferometric methods, which makes the design complex with the use of large number of polarization optics and produces space‐bandwidth limitations. The simultaneous extraction of Jones matrix elements with a compact system design is still a technical challenge in view of its potential applications in biomedical and real‐time characterization scenarios. In this paper, the imaging features of the in‐line holography are exploited to develop a compact polarization in‐line holography (PIH) system capable of single‐shot extraction of Jones‐matrix elements. The technique achieves simultaneous orthogonal polarization state generation and corresponding polarization multiplexed in‐line hologram detection by utilizing a compact polarization geometry. The imaging compatibility and measurement accuracy of the method is experimentally validated by the real‐time synthesis of Jones‐matrix elements corresponding to custom designed polarization sensitive samples and standard birefringent resolution target. Furthermore, to demonstrate the application of the system in dynamic imaging, the transient polarization changes of a custom‐designed parallel nematic liquid crystal display (LCD) are investigated. [ABSTRACT FROM AUTHOR]

An intriguing field of research has recently emerged in which biological cells can be demonstrated to behave as photonics devices, such as optical microlenses. This research highlights yeast cells as promising candidates for engineering biolenses with customizable focal properties. Typically serving as positive biolenses due to their quasi‐spherical shape and positive refractive index (RI) contrast, yeast cells can achieve a negative lensing effect by manipulating their intracellular content, without altering their overall morphology. In fact, it shows that exposure to hypotonic conditions induces the formation of a large, roundish vacuole with lower RI values with respect to the surrounding cytoplasm, thus altering the cell's optical properties. This behavior is investigated by using 3D RI tomograms obtained through a holo‐tomographic phase imaging flow cytometry system, demonstrating that the anisotropic nature of yeast cells results in focal properties dependent on their specific orientations in respect to the incident light. Furthermore, Zemax OpticStudio is utilized to perform comprehensive assessments for optical design analysis of the obtained cell biolenses. The methods described here and the related results represent a pioneering investigation of biological cells' metamorphoses via intracellular content manipulation for biolens applications. [ABSTRACT FROM AUTHOR]

In-line digital holography is a powerful tool widely used for microscopic object imaging. Usually, in-line and out-line configurations are used to implement holographic systems, but in-line-based set-ups are preferable as they are less sensitive to mechanical vibrations and refraction index variations. However, non-desired blurred conjugate images are superposed to the reconstructed object image by using in-line systems. One strategy to remove the conjugate image contribution is to include a double-sideband filter at the Fourier plane of the system. After using the filter, data obtained at the CCD are processed to retrieve the magnitude and phase (hologram) of the diffracted wavefront while removing the conjugated image. Afterwards, a diffraction integral equation is used to digitally propagate the hologram. Despite the above-mentioned factors, there is not a thorough analysis in the literature of magnification parameters associated with the final reconstructed image, this aspect being crucial for the experimental application of the above-stated approach. Under this scenario, a theoretical analysis of the longitudinal and transverse magnifications of the reconstructed images is provided in this work. The method is validated through the simulation and experimental results of different microscopic objects: glass microspheres, a micrometric reticle, and a resolution test chart USAF 1951. The obtained results provide that the combination of magnification relations with methods for hologram propagation and optimal focused image identification is effective for object position determination. This approach could be useful for 3D microparticle localization and monitoring with optimized magnification within real-time applications. [ABSTRACT FROM AUTHOR]

Current commercial air-quality monitoring devices lack a large dynamic range, especially at the small, ultrafine size scale. Furthermore, there is a low density of air-quality monitoring stations, reducing the precision with which local particulate matter hazards can be tracked. Here, we show a low-cost, lensfree, and portable air-quality monitoring device (LPAQD) that can detect and measure micron-sized particles down to 100 nm-sized particles, with the capability to track and measure particles in real time throughout a day and the ability to accurately measure particulate matter densities as low as 3 μg m–3. A vapor-condensed film is deposited onto the coverslip used to collect particles before the LPAQD is deployed at outdoor monitoring sites. The vapor-condensed film increases the scattering cross section of particles smaller than the pixel size, enabling the sub-pixel and sub-diffraction-limit-sized particles to be detected. The high dynamic range, low cost, and portability of this device can enable citizens to monitor their own air quality to hopefully impact user decisions that reduce the risk for particulate matter-related diseases. [ABSTRACT FROM AUTHOR]

Imaging is a longstanding research topic in optics and photonics and is an important tool for a wide range of scientific and engineering fields. Computational imaging is a powerful framework for designing innovative imaging systems by incorporating signal processing into optics. Conventional approaches involve individually designed optical and signal processing systems, which unnecessarily increased costs. Computational imaging, on the other hand, enhances the imaging performance of optical systems, visualizes invisible targets, and minimizes optical hardware. Digital holography and computer-generated holography are the roots of this field. Recent advances in information science, such as deep learning, and increasing computational power have rapidly driven computational imaging and have resulted in the reinvention these imaging technologies. In this paper, I survey recent research topics in computational imaging, where optical randomness is key. Imaging through scattering media, non-interferometric quantitative phase imaging, and real-time computer-generated holography are representative examples. These recent optical sensing and control technologies will serve as the foundations of next-generation imaging systems in various fields, such as biomedicine, security, and astronomy. [ABSTRACT FROM AUTHOR]

BackgroundEsophageal cancer management lacks reliable response predictors to chemotherapy. In this study we evaluated the feasibility and accuracy of Biodynamic Imaging (BDI), a technology that employs digital holography as a rapid predictor of chemotherapy sensitivity in locoregional esophageal adenocarcinoma.MethodsPre-treatment endoscopic pinch biopsies were collected from patients with esophageal adenocarcinoma during standard staging procedures. BDI analyzed the tumor samples and assessed in vitro chemotherapy sensitivity. BDI sensitivity predictions were compared to patients’ pathological responses, the gold standard for determining clinical response, in the surgically treated subset (n=18).ResultBDI was feasible with timely tissue acquisition, collection, and processing in all 30 enrolled patients and successful BDI analysis in 28/29 (96%) eligible. BDI accurately predicted chemotherapy response in 13/18 (72.2%) patients using a classifier for complete, marked, and partial/no-response. BDI technology had 100% negative predictive value for complete pathological response hence identifying patients unlikely to respond to treatment.ConclusionBDI technology can potentially predict patients’ response to platinum chemotherapy. Additionally, this technology represents a promising step towards optimizing treatment strategies for esophageal adenocarcinoma patients by pre-emptively identifying non-responders to conventional platinum-based chemotherapy.

The growing interest in the application of structured light has led to an increase in the use of spatial light modulators across users at all levels of experience. Hence, there is a need for software that controls the device, designs holograms and gathers experimental feedback. To meet these demands we present the Binary Complex Amplitude App - a standalone Matlab application that provides a graphic user interface with a full control of the Digital Micromirror Device, enabling hologram design and camera preview. We show that with all-in-one application, the user at any level of experience can operate the device and do not lose any of its capabilities.

We propose a compact, portable, and low-cost holographic microscope designed for the characterization of micrometric particles suspended in a liquid. This system is built around a commercial optical microscope by substituting its illumination source (a light-emitting diode) with a collimated laser beam. Similarly, a quartz flow cell replaces the microscope glass slide using a 3D-printed custom mount. With the hardware presented in this paper, the holographic imaging of the electromagnetic fields emitted by the particles that intercept the laser beam achieves a resolution close to that of optical microscopes but with a greater depth of field. Several morphological and optical features can be extracted from the holograms, including particle projected section, aspect ratio, and extinction cross-section. Additionally, we introduce a remote system control that enables users to process the acquired holograms on a remote computational device. This work provides a comprehensive description of the methodology of image processing in holographic microscopy and a series of validation measurements conducted using calibrated particles. This technique is suitable for the characterization of airborne particles found in snow, firn, and ice; here we report experimental results obtained from Alpine ice cores.

Exposure to bio-aerosols such as pollen can lead to adverse health effects. There is a need for a portable and cost-effective device for long-term monitoring and quantification of various types of pollen. To address this need, we present a mobile and cost-effective label-free sensor that takes holographic images of flowing particulate matter (PM) concentrated by a virtual impactor, which selectively slows down and guides particles larger than 6 μm to fly through an imaging window. The flowing particles are illuminated by a pulsed laser diode, casting their inline holograms on a complementary metal-oxide semiconductor image sensor in a lens-free mobile imaging device. The illumination contains three short pulses with a negligible shift of the flowing particle within one pulse, and triplicate holograms of the same particle are recorded at a single frame before it exits the imaging field-of-view, revealing different perspectives of each particle. The particles within the virtual impactor are localized through a differential detection scheme, and a deep neural network classifies the pollen type in a label-free manner based on the acquired holographic images. We demonstrated the success of this mobile pollen detector with a virtual impactor using different types of pollen (i.e., bermuda, elm, oak, pine, sycamore, and wheat) and achieved a blind classification accuracy of 92.91%. This mobile and cost-effective device weighs ∼700 g and can be used for label-free sensing and quantification of various bio-aerosols over extended periods since it is based on a cartridge-free virtual impactor that does not capture or immobilize PM.

Lysosomes are the terminal end of catabolic pathways in the cell, as well as signaling centers performing important functions such as the recycling of macromolecules, organelles, and nutrient adaptation. The importance of lysosomes in human health is supported by the fact that the deficiency of most lysosomal genes causes monogenic diseases called as a group Lysosomal Storage Diseases (LSDs). A common phenotypic hallmark of LSDs is the expansion of the lysosomal compartment that can be detected by using conventional imaging methods based on immunofluorescence protocols or overexpression of tagged lysosomal proteins. These methods require the alteration of the cellular architecture (i.e., due to fixation methods), can alter the behavior of cells (i.e., by the overexpression of proteins), and require sample preparation and the accurate selection of compatible fluorescent markers in relation to the type of analysis, therefore limiting the possibility of characterizing cellular status with simplicity. Therefore, a quantitative and label‐free methodology, such as Quantitative Phase Imaging through Digital Holographic (QPI‐DH), for the microscopic imaging of lysosomes in health and disease conditions may represent an important advance to study and effectively diagnose the presence of lysosomal storage in human disease. Here we proof the effectiveness of the QPI‐DH method in accomplishing the detection of the lysosomal compartment using mouse embryonic fibroblasts (MEFs) derived from a Mucopolysaccharidosis type III‐A (MSP‐IIIA) mouse model, and comparing them with wild‐type (WT) MEFs. We found that it is possible to identify label‐free biomarkers able to supply a first pre‐screening of the two populations, thus showing that QPI‐DH can be a suitable candidate to surpass fluorescent drawbacks in the detection of lysosomes dysfunction. An appropriate numerical procedure was developed for detecting and evaluate such cellular substructures from in vitro cells cultures. Results reported in this study are encouraging about the further development of the proposed QPI‐DH approach for such type of investigations about LSDs. [ABSTRACT FROM AUTHOR]

In digital holography, reconstructed image quality can be primarily limited due to the inability of a single small aperture sensor to cover the entire field of a hologram. The use of multi-sensor arrays in synthetic aperture digital holographic imaging technology contributes to overcoming the limitations of sensor coverage by expanding the area for detection. However, imaging accuracy is affected by the gap size between sensors and the resolution of sensors, especially when dealing with a limited number of sensors. An image reconstruction method is proposed that combines physical constraint characteristics of the imaging object with a score-based diffusion model, aiming to enhance the imaging accuracy of digital holography technology with extremely sparse sensor arrays. Prior information of the sample is learned by the neural network in the diffusion model to obtain a score function, which alternately constrains the iterative reconstruction process with the underlying physical model. The results demonstrate that the structural similarity and peak signal-to-noise ratio of the reconstructed images using this method are higher than the traditional method, along with a strong generalization ability. [ABSTRACT FROM AUTHOR]

Holographic techniques are indispensable tools for modern optical engineering. Over the past two decades, research about incoherent digital holography has continued to attract attention. Optical scanning holography (OSH) can obtain incoherent holograms using single-pixel detection and structured illumination with Fresnel zone patterns (FZPs). Particularly by changing the size of a detector, OSH can also obtain holograms under coherently illuminated conditions. Since 1979, OSH has continuously evolved. According to the evolution of semiconductor technology, spatial light modulators (SLMs) come to be useful for various imaging fields. By using SLM techniques for OSH, the practicality of OSH is improved. These SLM-based OSH methods are termed computational OSH (COSH). In this review, the configurations, recording and reconstruction methods, and proposed applications of COSH are reviewed. [ABSTRACT FROM AUTHOR]

In this paper, asynchronous dual-wavelength phase-shift interferometry is used to calibrate a line structure of a step height of 400 mm nominally standard based on the ISO 5436 profile analysis. The Hamming window: band-pass filter is used to assign accurately the detected point edge from the intersection of the experimental line edge from its simulation. The shifted off-axis interferograms are captured and corrected from noise. The corrected interferograms are wrapped by using the four-frame algorithm. The extracted phases at each wavelength are subtracted and the obtained phase map is converted to a height map. Experimental results show that the detected point edge of the step height standard being measured is assigned at filter order N = 901, cut-off frequency f0 = 0.39, and frequency bandwidth fb = 0.25. [ABSTRACT FROM AUTHOR]

We explore the principles, implementation details, and performance characteristics of a lensless multi-spectral digital holographic sensor and demonstrate its potential for quality assurance in semiconductor manufacturing. The method is based on capturing multi-spectral digital holograms, which are subsequently utilized to evaluate the shape of a reflective test object. It allows for a compact setup satisfying high demands regarding robustness against mechanical vibrations and thus overcomes limitations associated with conventional optical inspection setups associated with lens-based white light interferometry. Additionally, the tunable laser source enhances the versatility of the system and enables adaptation to various sample characteristics. Experimental results based on a wafer test specimen demonstrate the effectiveness of the method. The axial resolution of the sensor is ±2.5 nm, corresponding to 1σ.

Microplastics derived from fiber shredding are recognized by the scientific community as one of the main sources of microplastic water pollution, thus actualizing the need for techniques able to identify them with high accuracy. The recently released Holography Micro-Plastic Dataset offers the opportunity to test deep neural networks in their ability to distinguish between microplastics and other debris on a standard benchmark. The promising results obtained from the initial batch of experiments can be further improved through a combined approach which involves different image mapping techniques and recent state-of-the-art deep models. Within this framework, we analyze various image fusion schemas to merge the paired dataset images (amplitude and phase) into a single three-channel picture. We demonstrate that our proposed approach yields increased accuracy compared to both single-image data processing and other fusion techniques. Finally, the performance of our method is further enhanced by employing the Vision Transformer model as backbone, highlighting the effectiveness of the proposed approach in microplastics classification.

Incoherent digital holography (IDH) is a technique that enables single-shot three-dimensional (3D) imaging by recording holograms with incoherent light, such as sunlight and LEDs. IDH is expected to be a next-generation 3D measurement technique, but there are two challenges: speeding up both denoising required for IDH due to insufficient light and the diffraction calculations required to obtain reconstructed images. We propose a real-time IDH system in which single-exposure phase-shifting digital holography, which can record multiple phase-shifted holograms in a single exposure, is combined with an embedded graphic processing unit (GPU). The proposed system enables real-time color imaging of the real world from incoherent holograms with $2448 \times 2048$ pixels while reducing noise at 21.2 frames per second. The effect of the denoising was evaluated by speckle contrast, showing that noises were well reduced. Compared to five existing studies using field programable gate arrays and GPUs, the proposed system is capable of computing large hologram reproduction at high speed. The proposed system is a prototype for future incoherent holographic cameras.

We propose deep learning‐enhanced self‐interference incoherent digital holography. Self‐interference incoherent digital holography is a hologram acquisition technique under the incoherent light condition, which can capture the real‐world complex hologram. To overcome unwanted optical defects of the self‐interference, we suggest a data‐driven approach for reducing the additional noise and enhancing the image quality. [ABSTRACT FROM AUTHOR]

A method of dual-wavelength digital holographic interferometry for analyzing and controlling surface shape for technical applications, including surfaces exposed to high-temperature plasma in fusion reactors, is presented. The capability of applying the method both using miniature vertical-emitting diodes (VCSEL) and conventional wavelength-tunable lasers is shown. The research method is based on dual-wavelength digital holographic interferometry, in which the phases of wave fronts reflected from the object detected at different wavelengths are compared to provide information about the shape of the object. Moreover, the sensitivity of the method is determined by the value of synthetic wavelength, which depends on the difference of wavelengths used for acquisition of digital holograms. The method used following wavelengths 854.000–854.082 nm and 779.900–779.870 nm. Implementation of vertical-emitting diodes for dual-wave holographic interferometry methods is shown. It is found that such diodes have a coherence length of about 20 cm and similar to He-Ne laser. The dependence of the emission wavelength of such sources on the current has been examined and it is determined that the output wavelength deviates less than 1 % during 24 hours. The application of the holographic method has been demonstrated for measuring the shape of objects used in various technical applications (a car body part and a shielding element of the internal wall of the Tokamak fusion reactor). The results of the research illustrate the opportunity to apply the technique of dual-wavelength holographic interferometry to measure a shape of the technical objects surface of various types. It should be noted that other method such as fringe projection can also be used to solve such problems, but it does not work sufficiently on low-scattering surfaces, in our case the lacquered surface of the car body, or specular reflecting surfaces. In addition, the LIDAR technique requires scanning the surface over time, which can lead to measurement errors if the object is unstable due to mechanical movements or vibrations. In dualwavelength holographic interferometry such drawbacks can be reduced by short camera exposure times of milliseconds/ microseconds, or by using pulse laser with pulse durations of 10 ns. However, the major disadvantage of the method is the dependence of the mutual correlation of speckle structures of holograms on the wavelength difference. In order to increase the sensitivity of the method, it is necessary to increase this wavelength difference, and this can significantly reduce the signal-to-noise ratio and decrease the accuracy of the obtained data.

Digital holography is actively used for the characterization of objects and 3D-scenes, tracking changes in medium parameters, 3D shape reconstruction, detection of micro-object positions, etc. To obtain high-quality images of objects, it is often necessary to register a set of holograms or to select a noise suppression method for specific experimental conditions. In this paper, we propose a method to improve filtering in digital holography. The method requires a single hologram only. It utilizes interpolation upscaling of the reconstructed image size, filtering (e.g., median, BM3D, or NLM), and interpolation to the original image size. The method is validated on computer-generated and experimentally registered digital holograms. Interpolation methods coefficients and filter parameters were analyzed. The quality is improved in comparison with digital image filtering up to 1.4 times in speckle contrast on the registered holograms and up to 17% and 29% in SSIM and NSTD values on the computer-generated holograms. The proposed method is convenient in practice since its realization requires small changes of standard filters, improving the quality of the reconstructed image.

Digital holography has transformative potential for the measurement of stacked-chip microstructures due to its non-invasive, single-shot, full-field characteristics. However, significant light scattering and diffraction at steep edges in step microstructures cause the batwing effect, leading to measurement errors. Herein, we propose a standard-deviation-based adaptive median filter to eliminate batwing effects in step microstructure measurement using digital holography. The standard deviation determines the positions of the steps and the range of the batwing effect. During filtering, the filter window size varies: it adjusts according to the center’s position within the batwing effect range and reduces outside this range to prevent distortion in other regions. Filtering weights are set to maintain information integrity while using larger filter windows. Experiments on the Standard Resolution Target USAF 1951 and the standard step height target show that our method successfully eliminates batwings while preserving the integrity of the remaining profile.

Digital holography (DH) is an important method for three-dimensional (3D) imaging since it allows for the recording and reconstruction of an object's amplitude and phase information. However, the field of view (FOV) of a DH system is typically restricted by the finite size of the pixel pitch of the digital image sensor. We proposed a new configuration of the DH system based on Fresnel's bi-mirror to achieve doubling the camera FOV of the existing off-axis DH system which leveraged single-shot acquisition and a common-path optical framework. The dual FOV was obtained by spatial frequency multiplexing corresponding to two different information-carrying beams from an object. Experimental evidence of the proposed dual FOV-DH system's viability was provided by imaging two different areas of the test object and an application to surface profilometry by measuring the step height of the resolution chart which showed excellent agreement with an optical profiler. Due to the simple configuration, the proposed system could find a wide range of applications, including in microscopy and optical metrology. [ABSTRACT FROM AUTHOR]

Digital holography is a promising imaging technology. However, there is speckle noise in the reconstructed image of a digital hologram. Speckle degrades the quality of the reconstructed image. Suppression of speckle noise is a challenging problem in digital holography. A novel method is proposed to reduce speckle by a fast logistic adaptive non-local means (LA-NLM) algorithm. In the proposed method, the logistic function is incorporated into the weight calculation of the NLM algorithm to account for multiplicative speckle noise. Filtering parameters are dynamically adjusted according to the statistical property of speckle in the reconstructed image. To enhance computational efficiency, the proposed algorithm takes advantage of the integral image technique to speed up the calculation of the similarity between image patches. Simulated and experimental digital holograms are obtained to verify the proposed method. The results show that the speckle noise is effectively suppressed in digital holography. The proposed method is efficient and feasible, and can be applied to such fields as three-dimensional display, holographic measurement, and medical diagnosis. [ABSTRACT FROM AUTHOR]

Large amounts of lipids are stored inside lipid droplets by some microalgae. Since these lipids can be used to produce nutraceuticals and biodiesel in a sustainable way, research is developing on fast non-destructive methods to quantify and monitor the amount of lipids within microalgal cultures. In this paper, we have developed with digital holographic microscopy a fast quantitative method to assess the evolution of the lipid content inside the diatom Phaeodactylum tricornutum living cells. The method uses a specific processing of recorded hologram sequences based on the refocusing capability in digital holographic microscopy. In representative samples of the culture, inside living cells, each lipid droplet volume is evaluated. In those experiments, for each sample, more than one thousand lipid droplets are automatically analysed from a sequence of one hundred recorded holograms. We have validated the method thanks to correlative quantitative phase contrast-fluorescence imaging and extrapolated it to larger calibrated spherical refractive particles, to demonstrate the flexibility of the method. [ABSTRACT FROM AUTHOR]

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In this study, we have proposed a digital holographic technique in which the frequency-modulated continuous-wave technique is introduced as a novel implementation of wavelength multiplexing in the time–frequency domain. In the proposed technique, the holograms are recorded with two wavelengths and the information of each hologram can be separated in the time–frequency domain by modulating the frequencies of two laser diodes at different modulation widths. Therefore, a temporal Fourier analysis is performed on each pixel of the time-series holograms whose intensity is modulated with two beat frequencies. And then, the holograms corresponding to the two wavelengths are extracted independently. Initially, a holographic system with two close wavelengths of 782.43 nm and 782.50 nm was designed to measure the surface profile of metallic gauge blocks with a known step-height of 1.16 mm in both experimental and numerical calculations. In addition, the measurement accuracy of the proposed system was investigated using both the experimental and the numerical results. Furthermore, the numerical calculation was conducted to investigate the origin of the periodic noise superimposed on the experimental results. Finally, the reduction method of the periodic noise was proposed, and the effect of the method was demonstrated using numerical calculations. [ABSTRACT FROM AUTHOR]

Holography offers a vital platform for optical information storage and processing, which has a profound impact on many photonic applications, including 3D displays, LiDAR, optical encryption, and artificial intelligence. In this review, we provide a comprehensive overview of optical holography, moving from volume holography based on optically thick holograms to digital holography using ultrathin metasurface holograms in nanophotonics. We review the use of volume holograms for holographic multiplexing through the linear momentum selectivity and other approaches and highlight the emerging use of digital holograms that can be implemented by ultrathin metasurfaces. We will summarize the fabrication of different holographic recording media and digital holograms based on recent advances in flat meta-optics and nanotechnology. We highlight the rapidly developing field of metasurface holography, presenting the use of multi-functional metasurfaces for multiplexing holography in the use of polarization, wavelength, and incident angle of light. In the scope of holographic applications, we will focus on high bandwidth metasurface holograms that offer the strong sensitivity to the orbital angular momentum of light. At the end, we will provide a short summary of this review article and our perspectives on the future development of the vivid holography field. [ABSTRACT FROM AUTHOR]

In classical Fourier optics, an optical imaging system is regarded as a linear space-invariant system, which is only an approximation. Especially in digital holography, the space-variance effect has a great impact on the image quality and cannot be ignored. Therefore, it is comprehensively investigated in this article. Theoretical analyses indicate that the space-variance effect is caused by linear frequency modulation and ideal low-pass filtering, and it can be divided into three states: the approximate space-invariance state, the high-frequency distortion state, and the boundary-diffraction state. Classical Fourier optics analysis of optical imaging systems only considers the first. Regarding the high-frequency distortion state, the closer the image field is to the edge, the more severe the distortion of high-frequency information is. As for the boundary-diffraction state, in addition to the distortion of high-frequency information in the margin, a prominent boundary-diffraction phenomenon is observed. If the space-variance effect of the imaging lens is ignored, we predict that no space-variance effect in image holography will occur when the hologram is recorded at the back focal plane of the imaging lens. Simulation and experimental results are presented to validate our theoretical prediction. [ABSTRACT FROM AUTHOR]

Optical and digital images are one of the most important channels for transmitting information. At the Institute for Information Transmission Problems of the Russian Academy of Sciences (IITP RAS), this topic has always, since the founding of the institute, been given the closest attention. The institute's employees have made significant contributions to both the domestic and global science of image processing. In this work, the authors touched only on the main stages of the development of the theory, methods, and algorithms for image processing and analysis in the Laboratory of Digital Optics of the Institute for Information Transmission Problems of the Russian Academy of Sciences. [ABSTRACT FROM AUTHOR]

In-line digital holography is a powerful tool widely used for microscopic object imaging. Usually, in-line and out-line configurations are used to implement holographic systems, but in-line-based set-ups are preferable as they are less sensitive to mechanical vibrations and refraction index variations. However, non-desired blurred conjugate images are superposed to the reconstructed object image by using in-line systems. One strategy to remove the conjugate image contribution is to include a double-sideband filter at the Fourier plane of the system. After using the filter, data obtained at the CCD are processed to retrieve the magnitude and phase (hologram) of the diffracted wavefront while removing the conjugated image. Afterwards, a diffraction integral equation is used to digitally propagate the hologram. Despite the above-mentioned factors, there is not a thorough analysis in the literature of magnification parameters associated with the final reconstructed image, this aspect being crucial for the experimental application of the above-stated approach. Under this scenario, a theoretical analysis of the longitudinal and transverse magnifications of the reconstructed images is provided in this work. The method is validated through the simulation and experimental results of different microscopic objects: glass microspheres, a micrometric reticle, and a resolution test chart USAF 1951. The obtained results provide that the combination of magnification relations with methods for hologram propagation and optimal focused image identification is effective for object position determination. This approach could be useful for 3D microparticle localization and monitoring with optimized magnification within real-time applications.

Large amounts of lipids are stored inside lipid droplets by some microalgae. Since these lipids can be used to produce nutraceuticals and biodiesel in a sustainable way, research is developing on fast non-destructive methods to quantify and monitor the amount of lipids within microalgal cultures. In this paper, we have developed with digital holographic microscopy a fast quantitative method to assess the evolution of the lipid content inside the diatom Phaeodactylum tricornutum living cells. The method uses a specific processing of recorded hologram sequences based on the refocusing capability in digital holographic microscopy. In representative samples of the culture, inside living cells, each lipid droplet volume is evaluated. In those experiments, for each sample, more than one thousand lipid droplets are automatically analysed from a sequence of one hundred recorded holograms. We have validated the method thanks to correlative quantitative phase contrast–fluorescence imaging and extrapolated it to larger calibrated spherical refractive particles, to demonstrate the flexibility of the method.

Featured Application: This work will make it possible to easily set up snapshot holographic portrait studios and allow holographic portraits to be developed and disseminated to the public on a larger scale. For 60 years, high-energy pulsed lasers have enabled the recording of extremely realistic portraits of living people within a few nanoseconds. In the 21st century, this confidential technique, which requires great skill and equipment, has almost disappeared because of the final monochromatic color of the holograms, which does not appeal to the public. In this study, we show that ultra-realistic, full-color, and full-parallax snapshot holographic portraits can be recorded using a limited number of synchronized HD cameras. Experiments were successfully conducted using the digital CHIMERA holographic stereogram printing technique combined with image interpolation using a neural network. This new recording method allows holographic portraits to be developed and disseminated to the public on a larger scale. [ABSTRACT FROM AUTHOR]

To address the complexity of small or unique reconstruction distances in digital holography, we propose an inverse cross-correlation-based algorithm for the digital holographic imaging of multiplanar objects with a large depth of field. In this method, a planar output mapping is closely around the objects, and it is established by calculating the image inverse cross-correlation matrix of the reconstructed image at similar reconstruction distances, whereby the object edges serve as the result guide. Combining the search for edge planes with the depth estimation operator, the depth of field of digital holography is improved, thus allowing for a digital holography that is capable of meeting the requirements of the holographic imaging of multiplanar objects. Compared with the traditional depth estimation operator method, the proposed method solves the reconstruction ambiguity problem in multiple planes with a simple optical path, and no additional optical or mechanical devices need to be added, thus greatly improving the reconstruction quality. The numerical calculation results and the experimental results with multiplanar samples validate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

A robust method is proposed to reconstruct images with only one hologram in digital holography by introducing a deep learning (DL) network. The U-net neural network is designed according to DL principles and trained by the image data set collected using phase-shifting digital holography (PSDH). The training data set was established by collecting thousands of reconstructed images using PSDH. The proposed method can complete the holography reconstruction with only a single hologram and then benefits the space bandwidth product and relaxes the storage loads of PSDH. Compared with the results of PSDH, the results of deep learning are immune to most disturbances, including reference tilt, phase-shift errors, and speckle noise. Assisted by a GPU processor, the proposed reconstruction method can reduce the consumption time to almost one percent of the time needed by two-step PSDH. This method is expected to be capable of holography imaging with a single hologram, with high capacity, efficiently in the digital holography applications. [ABSTRACT FROM AUTHOR]

The measurement of cloud microphysical parameters plays an important role in describing characteristics of liquid phase clouds and investigating mutual relationships between clouds and precipitation. In this paper, cloud microphysical parameters at Liupan Mountain Weather Station in Ningxia are measured with a high-resolution coaxial digital holographic imager and a fog monitor 120. There are differences in the measurement results between the two instruments. The number concentration measured by the digital holographic imager is about 1.5 times that of the fog monitor 120. However, their Pearson correlation coefficient is above 0.9. Through analysis, we found that the measurement results of the digital holographic imager and fog monitor 120 are differences in 2–4 µm and 7–50µm. For the droplets with the diameters of 4–7 µm, their measurement results have good consistency. By analyzing the influence of wind field and detection sensitivity on the measurement principle, the reasons which caused the difference are proposed. Advice is given to observe topographic clouds by using the above two instruments. In addition, the differences in liquid water content and visibility are analyzed due to the absence of small and large droplets. The study provides data support for improving the accuracy of instruments in measuring cloud droplets and is useful for research in the field of cloud microphysical processes. [ABSTRACT FROM AUTHOR]

This study examines the use of optical encoding to prevent unauthorized access to various categories of information (including video) during operational transmission. Experimentally implemented holographic coding in spatially incoherent radiation of a 4K color video stream with digital input of information and dynamically changing coding elements-holograms was used to improve the quality of video stream coding and ensure high throughput of the coding system. High-resolution liquid-crystal spatial-temporal light modulators were used to input encoded video information and display holograms. The encoding method is based on registering an optical convolution of the input scene image with the encoding response of the hologram. In this case, individual color channels of each frame of the video stream are encoded in turn. Numerical methods of inverse filtering and regularization were used for decoding. The results of the present studies will be useful in creating a new generation of secure high-resolution video communication systems. [ABSTRACT FROM AUTHOR]

Coded aperture 3D imaging techniques have been rapidly evolving in recent years. The two main directions of evolution are in aperture engineering to generate the optimal optical field and in the development of a computational reconstruction method to reconstruct the object's image from the intensity distribution with minimal noise. The goal is to find the ideal aperture–reconstruction method pair, and if not that, to optimize one to match the other for designing an imaging system with the required 3D imaging characteristics. The Lucy–Richardson–Rosen algorithm (LR2A), a recently developed computational reconstruction method, was found to perform better than its predecessors, such as matched filter, inverse filter, phase-only filter, Lucy–Richardson algorithm, and non-linear reconstruction (NLR), for certain apertures when the point spread function (PSF) is a real and symmetric function. For other cases of PSF, NLR performed better than the rest of the methods. In this tutorial, LR2A has been presented as a generalized approach for any optical field when the PSF is known along with MATLAB codes for reconstruction. The common problems and pitfalls in using LR2A have been discussed. Simulation and experimental studies for common optical fields such as spherical, Bessel, vortex beams, and exotic optical fields such as Airy, scattered, and self-rotating beams have been presented. From this study, it can be seen that it is possible to transfer the 3D imaging characteristics from non-imaging-type exotic fields to indirect imaging systems faithfully using LR2A. The application of LR2A to medical images such as colonoscopy images and cone beam computed tomography images with synthetic PSF has been demonstrated. We believe that the tutorial will provide a deeper understanding of computational reconstruction using LR2A. [ABSTRACT FROM AUTHOR]