Application Of Digital Holography Research Articles

Single-pixel deep phase-shifting incoherent digital holography

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

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

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

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

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

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

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

Robust Holographic Reconstruction by Deep Learning with One Frame

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.

High-resolution reconstruction of spectrum-overlapped off-axis holography by deflecting reference beam of Gaussian symmetry

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

Emerging scientific and industrial applications of digital holography: an overview

Abstract Holography is a technique to record and reconstruct three dimensional (3D) information without mandating lenses. Digital holography (DH) provides direct access to the complex amplitude of the reconstructed wavefront. This feature differentiates DH from other imaging techniques and enables it to provide quantitative information of the object under investigation. Advancements in technologies of digital image sensors, coherent sources, and computation algorithms and hardware, has paved the way of digital holographic systems for industrial applications. This work presents an overview of the scientific and industrial applications where DH can play an important role. Few of the applications of digital holographic systems in the industrial and scientific areas including microscopy, non-destructive testing, displays, environment, cloud and ocean studies are discussed.

Digital Holographic Interferometry for Wholefield NDT Applications

Holographic interferometry is a non-contact whole field optical technique used as a powerful NDT tool. This technique is highly sensitive and maps the object surface deformation as holographic fringe pattern. Conventional holography technique has practical difficulties in recording and reconstructing holograms. With the development in imaging sensor technology and fast algorithms in image processing, digital holography has been established. Digital holography uses high-resolution digital camera for recording holograms and does reconstruction of holograms numerically using a computer. This has enhanced the scope and application of holography for NDT many fold. In this paper application of digital holography to non-destructive testing is presented. The basic principle of digital holography and digital holographic interferometry in obtaining double exposure hologram for NDT is described. The software developed in house for numerical reconstruction of holograms is also explained. The advantages of digital holography over conventional holography in NDT applications are highlighted. Extensive experiments were carried out to prove the detectability of defects in both metallic and non-metallic materials and the results are presented. It is shown that digital holography is able to identify defects in a wide range of materials with great ease because of its high sensitivity and whole field nature.

Recent Advances in Pollution Control and Sustainable Energy by Application of Digital Holography for Optimised Results

Recent Advances in Pollution Control and Sustainable Energy by Application of Digital Holography for Optimised Results

Analysis of the oscillations induced by a supersonic jet applied to produce nanofibers

High-performance fibers are key components for enhancing the mechanical properties of composite materials. The development of high strength nanofibers augurs the production of new nano-composites with outstanding features. However, the robust production of continuous glass nanofibers that can be feasible processed for efficiently manufacturing nanocomposites is still challenging. Recently, Cofiblas (Continuous Fiberizing by Laser melting and Supersonic dragging) was demonstrated as a technique capable of producing continuous glass nanofibers with unlimited length. Cofiblas process has some similarities with the widely known melt blowing technique for the production of polymeric fibers. In both techniques, the design of the gas nozzle is key to ensure the feasibility of the process since the turbulences of the gas jet may induce strong whipping of the filament.This paper gives novel experimental evidences on the correlation of the supersonic gas jet instabilities with the oscillation of the filament in the melt-blowing and Cofiblas processes, relating these oscillations with the presence of shock waves and unsteadiness in the flow, and gives valuable insight into the use of supersonic jets in the melt blowing process as an effective approach for the formation of nanofibers. A thin 3D-axisymmetric model in OpenFOAM® was put to test by comparing the performance of different solvers which were validated by flow visualization of the exit jet using digital holography (DH). In order to perform a realistic and thorough validation, we simulated the optical measurements of the flow from the CFD simulations of the mass density by Abel transform and numerical differentiation. The application of digital holography as the flow visualization technique makes possible both a precise validation of the density maps obtained from the Abel transformation of the 2D-alike results, and the analysis of the shockwave pattern in the air jet. Conversely, the numerical reconstruction of time-averaged holograms is employed to detect unsteadiness in the flow and to analyze the fiber oscillation, which is essential to assess the stability of the process. Lastly, the analysis and comparison of the vibration of the filament using the basic design and the optimized nozzle demonstrates a clear influence of the shock waves and flow unsteadiness in the stability of the filament.

Reduction of speckle noise in digital holography using a neighborhood filter based on multiple sub-reconstructed images.

The application of digital holography in several fields is limited since speckle destroys the original information of the reconstructed image. This paper proposes a neighborhood filter based on multiple sub-reconstructed images according to the random distribution of speckle noise. In this method, the denoised value is equal to the weighted sum of neighboring pixel values, and the weight is calculated by the degree of correlation between different positions of multiple sub-holograms. The experimental results show that the method can greatly reduce the speckle noise, and its noise reduction performance is superior to traditional digital image processing algorithms.

Compression strategies for digital holograms in biomedical and multimedia applications

While 60 years of successful application of holography is celebrated in this special issue, efficient representation and compression of holographic data has received relatively little attention in research. Notwithstanding this observation, and particularly due to the digitization that is also penetrating the holographic domain, interest is growing on how to efficiently compress holographic data such that interactive exchange of content, as well as digital storage can be facilitated proficiently. This is a particular challenge, not only because of its interferometric nature and the various representation formats, but also the often extremely large data volumes involved in pathological, tomographic, or high-end visualization applications. In this paper, we provide an overview of the state of the art in compression techniques and corresponding quality metrics for various practical applications in digital holography. We also consider the future by analyzing the emerging trends for addressing the key challenges in this domain.

The application of digital holography for accurate three-dimensional localisation of mosquito-bednet interaction

Understanding mosquito interaction with long-lasting insecticidal bednets is crucial in the development of more effective intervention methods to protect humans from malaria transmission. As such, a 240 × 240 × 1000 mm laboratory setup for the in-line recording of digital holograms and subsequent in-focus reconstruction and 3D localisation of mosquitoes is presented. Simple bednet background removal methods are used to accurately localise a mosquito obscured by a bednet in 3D coordinates. Simulations and physical data demonstrate that this method is suitable for mosquitoes positioned 3−1000 mm behind a bednet. A novel post-processing technique, involving a cascade-correlation of a Tamura of Intensity focus metric extracted from digitally reconstructed scenes, accurately localises mosquitoes positioned 35−100 mm behind a bednet from a single digital hologram. The result of this study is a scalable digital holographic methodology to examine mosquito-bednet interaction in 3D at a level of accuracy previously only seen in 2D imaging of mosquitoes in a much smaller volume.

Noncontact temperature measurement of human hand skin using volume phase holographic optical element based digital holographic interferometer

Measurement of surface temperature of human body skin is one of the basic and standard diagnostic tool for health management. The temperature of the human body is a vital sign of health status and it is used for medical diagnosis. Generally, contact type temperature sensors are used for temperature monitoring; however, accuracy of these sensors is limited due to the skin-sensor interface, sensor physical dimensions, and sensor pressure. This paper demonstrates an application of digital holography to measure the temperature of human hand skin (index finger and palm skin). The heat energy emitted from the human body flows as convection current in the air and cause a change in refractive index in air field around human body which leads to change in phase of object wave. A volume phase holographic optical element based digital holographic interferometric (DHI) system has been used in a lensless Fourier transform (LLFT) configuration to measure the temperature of human skin from the reconstructed phase difference of air surrounding the human body and ambient air. The surface temperature of human skin measured by volume phase holographic optical element based DHI system shows a good agreement with the temperature measured by a commercially available digital and infrared thermometer.

Deep learning for digital holography: a review.

Recent years have witnessed the unprecedented progress of deep learning applications in digital holography (DH). Nevertheless, there remain huge potentials in how deep learning can further improve performance and enable new functionalities for DH. Here, we survey recent developments in various DH applications powered by deep learning algorithms. This article starts with a brief introduction to digital holographic imaging, then summarizes the most relevant deep learning techniques for DH, with discussions on their benefits and challenges. We then present case studies covering a wide range of problems and applications in order to highlight research achievements to date. We provide an outlook of several promising directions to widen the use of deep learning in various DH applications.

Digital Holography and 3D Imaging 2020: introduction to the feature issue.

This feature issue of JOSA A and Applied Optics is dedicated to the fourteenth OSA Topical Meeting "Digital Holography and 3D Imaging" held 22-26 June 2020 in a virtual meeting. The conference, taking place every year, is a focal point for global technical interchange in the field of digital holography and 3D imaging, providing premier opportunities for people working in the field to present their new advances in research and development. Papers presented at the meeting highlight current research in digital holography and three-dimensional imaging, including interferometry, phase microscopy, phase retrieval, novel holographic processes, 3D and novel holographic displays, integral imaging, computer-generated holograms, compressive holography, 3D holographic display, AR display, full-field tomography, specific image and signal processing, and holography with various light sources, including coherent to incoherent and x-ray to terahertz waves. Techniques of digital holography and of 3D imaging have numerous applications, such as the state-of-the-art technological developments that are currently underway and stimulate further novel applications of digital holography and 3D imaging in biomedicine, deep learning, and scientific and industrial metrologies.

Digital Holography and 3D Imaging 2020: introduction to the feature issue.

This feature issue of JOSA A and Applied Optics is dedicated to the fourteenth OSA Topical Meeting "Digital Holography and 3D Imaging" held 22-26 June 2020 in a virtual meeting. The conference, taking place every year, is a focal point for global technical interchange in the field of digital holography and 3D imaging, providing premier opportunities for people working in the field to present their new advances in research and development. Papers presented at the meeting highlight current research in digital holography and three-dimensional imaging, including interferometry, phase microscopy, phase retrieval, novel holographic processes, 3D and novel holographic displays, integral imaging, computer-generated holograms, compressive holography, 3D holographic display, AR display, full-field tomography, specific image and signal processing, and holography with various light sources, including coherent to incoherent and x-ray to terahertz waves. Techniques of digital holography and of 3D imaging have numerous applications, such as the state-of-the-art technological developments that are currently underway and have also stimulated further novel applications of digital holography and 3D imaging in biomedicine, deep learning, and scientific and industrial metrologies.

Delamination testing of polyurethane pads adhered to polishing tool using a digital holographic nondestructive testing method

We demonstrate an application of digital holography for detection of a new type of defect, i.e., delamination of polyurethane pads on a polishing tool used on a high-speed computerized numerical control machine for production of precision optics. The method enabled us to acquire both qualitative and quantitative information about the delaminated region in the polishing pad. A delaminated region of 13.6 mm × 10.8 mm is detected and measured on the surface of the polishing pad. An increase in the delaminated region by 30% is noticed after completion of the polishing process with the delaminated polishing pad. The effect of delamination of the polishing pad on an optical surface is experimentally demonstrated using it for polishing a BK-7 glass substrate. These investigations may enable production of improved quality precision optics at the commercial level.

Terahertz digital holographic imaging

This tutorial describes the application of digital holography to the terahertz spectral region and demonstrates how to reconstruct images of complex dielectric targets. Using highly coherent terahertz sources, high-fidelity amplitude and phase reconstructions are achieved, but because the millimeter-scale wavelengths approach the decimeter-sized targets and optical components, undesirable aperture diffraction degrades the quality of the reconstructions. Consequently, off-axis terahertz digital holography differs significantly from its visible light counterpart. This tutorial addresses these challenges within the angular spectrum method and the Fresnel approximation for digital hologram reconstruction, from which the longitudinal and transverse resolution limits may be specified. We observed longitudinal resolution ( λ / 284 ) almost two times better than has been achieved with visible light digital holographic microscopy and demonstrate that submicrometer longitudinal resolution is possible using millimeter wavelengths for an imager limited ultimately by the phase stability of the terahertz source and/or receiver. Minimizing the number of optical components, using only large reflective optics, maximizing the angle of the off-axis reference beam, and judicious selection of spatial frequency filters all contribute to improve the quality of the reconstructed image. As in visible wavelength analog holography, the observed transverse resolution in terahertz digital holography is comparable to the wavelength but improves for features near the edge of the imaged object compared with features near the center, a behavior characterized by a modified description of the holographic transfer function introduced here. Holograms were recorded by raster scanning a sensitive superheterodyne receiver, and several visibly transparent and opaque dielectric structures were quantitatively examined to demonstrate the compelling application of terahertz digital holography for nondestructive test, evaluation, and analysis.

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

The OSA Topical Meeting on Digital Holography and 3D Imaging (DH) was held June 25-June 28, 2018, in Orlando, Florida, USA. Feature issues based on the DH meeting series have been released by Applied Optics (AO) since 2007. This year, AO and the Journal of the Optical Society of America A (JOSA A) jointly decided to have one such feature issue in each journal. This feature issue includes thirty-eight papers in AO and nine in JOSA A, and covers a large range of topics, reflecting the rapidly expanding techniques and applications of digital holography and 3D imaging. The upcoming DH Conference (DH 2019) will be held May 19-May 23 in Bordeaux, France.