Dynamic full-color digital holographic 3D display on single DMD

Digital holography has high potentials for future 3D imaging and display technology.We present a method for a dynamic full-color digital holographic 3D display on single digital micro-mirror device(DMD)with full-color,high-speed and high-fidelity characteristics.We combine the square regions of adjacent micro-mirrors into super-pixels that can modulate amplitude and phase independently.Gray images are achieved by amplitude modulation and precise positioning of each color is achieved by phase modulation.The proposed method realizes a full-color imaging based on the three primary colors and achieves measured structural similarity of more than 88%and color similarity of more than 98%,while retaining the high switch speed of 9 kHz,thus achieving dynamic full-color 3D display on charge-coupled device(CCD).

Non-isoplanatic lens aberration correction in dark-field digital holographic microscopy for semiconductor metrology

In the semiconductor industry,the demand for more precise and accurate overlay metrology tools has increased because of the continued shrinking of feature sizes in integrated circuits.To achieve the required sub-nanometre precision,the current technology for overlay metrology has become complex and is reaching its limits.Herein,we present a dark-field digital holographic microscope using a simple two-element imaging lens with a high numerical aperture capable of imaging from the visible to near-infrared regions.This combination of high resolution and wavelength coverage was achieved by combining a simple imaging lens with a fast and accurate correction of non-isoplanatic aberrations.We present experimental results for overlay targets that demonstrate the capability of our computational aberration correction in the visible and near-infrared wavelength regimes.This wide-ranged-wavelength imaging system can advance semiconductor metrology.

Thioacetamide Additive Homogenizing Zn Deposition Revealed by In Situ Digital Holography for Advanced Zn Ion Batteries

Zinc ion batteries are considered as potential energy storage devices due to their advantages of low-cost,high-safety,and high theoretical capacity.However,dendrite growth and chemical corrosion occurring on Zn anode limit their commercialization.These problems can be tackled through the optimization of the electrolyte.However,the screening of electrolyte additives using normal electrochemical methods is time-consuming and labor-intensive.Herein,a fast and simple method based on the digital holography is developed.It can realize the in situ monitoring of electrode/electrolyte interface and provide direct information concerning ion concentration evolution of the diffusion layer.It is effective and time-saving in estimating the homogeneity of the deposition layer and predicting the tendency of dendrite growth,thus able to value the applicability of electrolyte additives.The feasibility of this method is further validated by the forecast and evaluation of thioacetamide additive.Based on systematic characterization,it is proved that the introduction of thioacetamide can not only regulate the interficial ion flux to induce dendrite-free Zn deposition,but also construct adsorption molecule layers to inhibit side reactions of Zn anode.Being easy to operate,capable of in situ observation,and able to endure harsh conditions,digital holography method will be a promising approach for the interfacial investigation of other battery systems.

Resolution enhancement of digital holographic microscopy via synthetic aperture:a review

Digital holographic microscopy(DHM),which combines digital holography with optical microscopy,is a wide field,minimally invasive quantitative phase microscopy(QPM)approach for measuring the 3D shape or the inner structure of transparent and translucent samples.However,limited by diffraction,the spatial resolution of conventional DHM is relatively low and incompatible with a wide field of view(FOV)owing to the spatial bandwidth product(SBP)limit of the imaging systems.During the past decades,many efforts have been made to enhance the spatial resolution of DHM while preserving a large FOV by trading with unused degrees of freedom.Illumination modulation techniques,such as oblique illumination,structured illumination,and speckle illumination,can enhance the resolution by adding more high-frequency information to the recording system.Resolution enhancement is also achieved by extrapolation of a hologram or by synthesizing a larger hologram by scanning the sample,the camera,or inserting a diffraction grating between the sample and the camera.For on-chip DHM,spatial resolution is achieved using pixel super-resolution techniques.In this paper,we review various resolution enhancement approaches in DHM and discuss the advantages and disadvantages of these approaches.It is our hope that this review will contribute to advancements in DHM and its practical applications in many fields.

Antifouling mechanism of natural product-based coatings investigated by digital holographic microscopy

Using natural product-based antifouling coatings has proven to be an effective strategy to combat biofouling.However,their antifouling mechanisms are still unclear.In this study,the antifouling mechanism of natural product-based coatings consisting of bio-sourced poly(lactic acid)-based polyurethane and ecofriendly antifoulant(butenolide)derived from marine bacteria was revealed by observing 3D bacterial motions utilizing a 3D tracking technique-digital holographic microscopy(DHM).As butenolide content increases,the density of planktonic marine bacteria(Pseudomonas sp.)near the surface decreases and thus leads to a reduced adhesion,indicating that butenolide elicits the adaptive response of Pseudomonas sp.to escape from the surface.Meanwhile,among these remained cells,an increased percentage is found to undergo subdiffusive motions compared with the case of smaller dose of butenolide.Further experiments show that butenolide can accelerate their swimming velocity and reduce flick frequency.Antibacterial assay confirms that butenolide-based coating shows high efficacy of antifouling performance against Pseudomonas sp.but without killing them like 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one(DCOIT).

Integrated self-referencing single shot digital holographic microscope and optical tweezer

Digital holographic microscopy is a single-shot technique for quantitative phase imaging of samples,yielding thickness profiles of phase objects.It provides sample features based on their morphology,leading to their classification and identification.However,observing samples,especially cells,in fluids using holographic microscopes is difficult without immobilizing the object.Optical tweezers can be used for sample immobilization in fluids.The present manuscript provides an overview of our ongoing work on the development of a compact,low-cost microscopy system for digital holographic imaging of optically trapped samples.Integration of digital holographic microscopy system with tweezers is realized by using the optical pickup unit extracted from DVD burners to trap microsamples,which are then holographically imaged using a highly compact self-referencing interferometer along with a low-cost,in-house developed quadrant photodiode,providing morphological and spectral information of trapped particles.The developed integrated module was tested using polystyrene microspheres as well as human erythrocytes.The investigated system offers a multitude of sample features,including physical and mechanical parameters and corner frequency information of the sample.These features were used for sample classification.The proposed technique has vast potential in opening up new avenues for low-cost,digital holographic imaging and analysis of immobilized samples in fluids and their classification.

3D visualization using pulsed and CW digital holographic tomography techniques

We outline the use of digital holographic tomography to determine the three-dimensional （3D） shapes of falling and static objects, such as lenslets and water droplets. Reconstruction of digitally recorded inline holograms is performed using multiplicative and Radon transform techniques to reveal the exact 3D shapes of the objects.

Perfect digital holographic imaging with high resolutionusing a submillimeter-dimension CCD sensor

In order to improve the resolution of digital holography with a common-dimension charge-coupled device (CCD) sensor, the point spread functions are briefly derived for the commonly used and practical post-magnification, pre-magnification, and image-plane digital holographic microscopic systems. The ultimate resolutions of these systems are analyzed and compared. The results show that the ultimate lateral resolution of pre-magnification digital holography is superior to that of post-magnification digital holography in the same conditions. We also demonstrate that the ultimate lateral resolution of image-plane digital holography has no correlation with the photosensitive dimension of the CCD sensor, and it is not significantly related to the pixel size of the sensor. Moreover, both the ultimate resolution and the imaging quality of image-plane digital holography are superior to that of pre- and post-magnification digital holographic microscopy. High-resolution imaging, whose resolution is close to the ultimate resolution of the microscope objective, can be achieved by image-plane digital holography even with a submillimeter-dimension sensor. This system, by which perfect imaging can be achieved, is optimal for commonly used digital holographic microscopy. Experimental results demonstrate the correctness of the theoretical analysis.

A Preliminary Study on the Evaluation of Human Sperm Head Morphology with a Domestic Digital Holographic Image System

The head of sperm was imaged with domestic digital holographic microscopy(DHM),and then the quantitative three-dimensional size information of normal sperm and teratozoospermic sperm was compared and analyzed.DHM sperm imaging and repeated quantitative evaluation were used to determine the morphology of the sperm head in two patients with teratozoospermia and four volunteers with normal semen parameters.Sixty and 139 sperm of teratozoospermia patients and normal people were photographed by digital hologram,respectively.The differences in head height and width were compared and statistically analyzed.The sperm head height of the teratozoospermia group was 3.06±1.66μm,which was significantly lower than that of the normal sperm group(4.54±1.60μm,p<0.01),but there was no significant difference in the head width between the two groups.Compared with the traditional two-dimensional optical microscope observation method,the DHM system can provide three-dimensional quantitative information for the sperm head and thus may help in the comprehensive clinical evaluation of the sperm head structure.

Multiframe full-field heterodyne digital holographic microscopy

Digital holographic microscopy using multiframe full-field heterodyne technology is discussed in which two acousto-optic modulators are applied to generate low-frequency heterodyne interference and a high-speed cam- era is applied to acquire multiframe full-field holograms. We use a temporal frequency spectrum analysis algo- rithm to extract the object＇s information. The twin-image problem can be solved and the random noise can be significantly suppressed. The relationship between the frame number and the reconstruction accuracy is dis- cussed. The typical objects of microlenses and biology cells are reconstructed well with lO0-frame holograms for illustration.

Multi-prior physics-enhanced neural network enables pixel super-resolution and twin-imagefree phase retrieval from single-shot hologram

Digital in-line holographic microscopy(DIHM)is a widely used interference technique for real-time reconstruction of living cells’morphological information with large space-bandwidth product and compact setup.However,the need for a larger pixel size of detector to improve imaging photosensitivity,field-of-view,and signal-to-noise ratio often leads to the loss of sub-pixel information and limited pixel resolution.Additionally,the twin-image appearing in the reconstruction severely degrades the quality of the reconstructed image.The deep learning(DL)approach has emerged as a powerful tool for phase retrieval in DIHM,effectively addressing these challenges.However,most DL-based strategies are datadriven or end-to-end net approaches,suffering from excessive data dependency and limited generalization ability.Herein,a novel multi-prior physics-enhanced neural network with pixel super-resolution(MPPN-PSR)for phase retrieval of DIHM is proposed.It encapsulates the physical model prior,sparsity prior and deep image prior in an untrained deep neural network.The effectiveness and feasibility of MPPN-PSR are demonstrated by comparing it with other traditional and learning-based phase retrieval methods.With the capabilities of pixel super-resolution,twin-image elimination and high-throughput jointly from a single-shot intensity measurement,the proposed DIHM approach is expected to be widely adopted in biomedical workflow and industrial measurement.

Holographic storage scheme based on digital signal processing

In this paper, a holographic storage scheme for multimedia data storage and retrieval based on the digital signal processing (DSP) is designed. A communication model for holographic storage system is obtained on the analogy of traditional communication system. Many characteristics of holographic storage are embodied in the communication model. Then some new methods of DSP including two-dimensional (2-D) shifting interleaving, encoding and decoding of modulation-array (MA) code and method of soft-decision, etc. are proposed and employed in the system. From the results of experiments it can be seen that those measures can effectively reduce the influence of noise. A segment of multimedia data, including video and audio data, is retrieved successfully after holographic storage by using those techniques.

Microsphere-assisted quantitative phase microscopy:a review

Light microscopes are the most widely used devices in life and material sciences that allow the study of the interaction of light with matter at a resolution better than that of the naked eye.Conventional microscopes translate the spatial differences in the intensity of the reflected or transmitted light from an object to pixel brightness differences in the digital image.However,a phase microscope converts the spatial differences in the phase of the light from or through an object to differences in pixel brightness.Interference microscopy,a phase-based approach,has found application in various disciplines.While interferometry has brought nanometric axial resolution,the lateral resolution in quantitative phase microscopy(QPM)has still remained limited by diffraction,similar to other traditional microscopy systems.Enhancing the resolution has been the subject of intense investigation since the invention of the microscope in the 17th century.During the past decade,microsphere-assisted microscopy(MAM)has emerged as a simple and effective approach to enhance the resolution in light microscopy.MAM can be integrated with QPM for 3D label-free imaging with enhanced resolution.Here,we review the integration of microspheres with coherence scanning interference and digital holographic microscopies,discussing the associated open questions,challenges,and opportunities.

In-Fiber Thermally Diffused Coupler and Fiber Bragg Grating Inscribed in Twin-Core Fiber for Sensitivity-Enhanced Vector Bending Sensing

A vector bending fiber sensor based on core-by-core inscribed fiber Bragg gratings in a twin-core fiber has been proposed and experimentally demonstrated.An in-fiber integrated vector bending sensor is realized by using the thermal diffusion technique to fabricate the coupler.The characteristics of the coupler fabricated by thermal diffusion are simulated and experimented.By inscribing fiber Bragg gratings with different reflection wavelengths in the two cores of a symmetrical twin-core fiber,the curvature sensitivity can be enhanced by tracking the wavelength difference between the fiber Bragg gratings of the two cores.The measured bending sensitivity of the fiber Bragg grating ranges from–161.6 pm/m^(−1) to+165.5 pm/m^(−1).The differential sensitivity of the two cores is twice that of a conventional single grating,and the temperature-induced crosstalk is also reduced.The bending sensor proposed in this paper has the advantages of high integration,enhancing the sensitivity and two-dimensional orientation recognizability,and reducing temperature crosstalk,which can be a promising candidate for structural health monitoring or wearable artificial electronics applications.

Prediction of photothermal phase signatures from arbitrary plasmonic nanoparticles and experimental verification

We present a new approach for predicting spatial phase signals originating from photothermally excited metallic nanoparticles of arbitrary shapes and sizes.The heat emitted from such a nanoparticle affects the measured optical phase signal via changes in both the refractive index and thickness of the nanoparticle surroundings.Because these particles can be bio-functionalized to bind certain biological cell components,they can be used for biomedical imaging with molecular specificity,as new nanoscopy labels,and for photothermal therapy.Predicting the ideal nanoparticle parameters requires a model that computes the thermal and phase distributions around the particle,thereby enabling more efficient phase imaging of plasmonic nanoparticles and avoiding trial-and-error experiments while using unsuitable nanoparticles.The proposed nonlinear model is the first to enable the prediction of phase signatures from nanoparticles with arbitrary parameters.The model is based on a finite-volume method for geometry discretization and an implicit backward Euler method for solving the transient inhomogeneous heat equation,followed by calculation of the accumulative phase signal.To validate the model,we compared its results with experimental results obtained for gold nanorods of various concentrations,which we acquired using a custom-built wide-field interferometric phase microscopy system.

Review of Fresnel incoherent correlation holography with linear and non-linear correlations

Fresnel incoherent correlation holography(FINCH)is a well-established incoherent imaging technique.In FINCH,three selfinterference holograms are recorded with calculated phase differences between the two interfering,differently modulated object waves and projected into a complex hologram.The object is reconstructed without the twin image and bias terms by a numerical Fresnel back propagation of the complex hologram.A modified approach to implement FINCH by a single camera shot by pre-calibrating the system involving recording of the point spread function library and reconstruction by a nonlinear cross correlation has been introduced recently.The expression of the imaging characteristics from the modulation functions in original FINCH and the modified approach by pre-calibration in spatial and polarization multiplexing schemes are reviewed.The study reveals that a reconstructing function completely independent of the function of the phase mask is required for the faithful expression of the characteristics of the modulating function in image reconstruction.In the polarization multiplexing method by non-linear cross correlation,a partial expression was observed,while in the spatial multiplexing method by non-linear cross correlation,the imaging characteristics converged towards a uniform behavior.

Theoretical and experimental studies of the transport process of micro-particles in static water

A theoretical model is established in this paper to investigate the micro-particle behavior in the static water. The forces acting on the micro-particles are analyzed to obtain a description of the micro-particle behavior in the static water. It is shown that the velocity of the micro-particles is a function of the diameter of the micro-particles, the density of the fluid and the micro-particles, the viscosity and the time. The micro-particle＇s motion undergoes an accelerating period and a constant velocity period, and the acceleration period of small micro-particles is very short, its velocity is much smaller than that of larger ones. The net flux of a control-volume in the flow field is calculated combined with the Fick Law. It is shown that the transport coefficient is a function of the diameter of the micro-particles, the density of the fluid and the micro-particles, the viscosity and the temperature. The transport of smaller particles is more extended than the larger ones. The digital holography technology is applied to detect the micro-particle＇s motion and the comparison between the theoretical solution and the experimental results is made, with a quantitative agreement between them.