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Schematic chart of the used methodology used where the images depicted in the chart correspond with experimental results obtained with the proposed approach.
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An approach that allows superresolution imaging of three-dimensional (3-D) samples by numerical refocusing is presented in the field of digital holographic microscopy. Based on the object's spectrum shift produced by tilted illumination, we present a time multiplexing superresolved approach to overcome the Abbe's diffraction limit. The proposed app...
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... hologram. Thus, according to this procedure, it is possible to reconstruct a superresolved wave field of the object by numerically propagating each elementary pupil at different reconstruction distances and by assembling a SA where each propagated pupil is properly placed to its original position at the object's spectrum. The diagram depicted in Fig. 3 shows the whole process for 3-D superresolution imaging. But because of each hologram will have different recording phase conditions due to several reasons, three main different phase corrections must be taken into account in order to synthesize a high quality superresolved image. The first one is related with the addition of a global ...
Citations
... The use of a shorter wavelength to enhance the resolution of DHM is one way of them [10]. The second type of methods is to increase the illumination NA by oblique illumination [11][12][13][14][15][16][17], structured illumination (SI) [18][19][20][21][22][23][24], speckle illumination [25][26][27][28], or to enlarge the NA of the recording system by hologram extrapolation [29,30], hologram synthesis [31,32] and pixel super-resolution [33,34]. Another type of techniques is the use of deep learning to retrieve the high-resolution image without any prior knowledge about the imaging model [35]. ...
A dual-wavelength resolution-matching digital holographic microscopy with one path structured illumination is presented, which can improve phase imaging resolution. In this configuration, a dual-wavelength hologram with two illumination modes corresponding to two different wavelengths can be flexibly recorded at one shot, and the imaging resolutions under the two wavelengths can reach equivalence by setting the modulation frequency of structure illumination. The expression for calculating the modulation frequency of structured illumination in a two-wavelength system is given. By setting the proper modulation frequency, the resolution of dual-wavelength phase imaging can be enhanced, which is verified in the phase imaging experiment of a USAF quantitative phase target. The dual-wavelength reconstructed phase map of paramecia cells exhibit the internal macronucleus, food vacuole and cilia. The imaging results demonstrate the resolution-matching approach using one path structured-illumination in effect for the improvement of phase imaging resolution.
... This pattern, or hologram, encodes the complete electric field and can be reconstructed into amplitude and quantitative phase images at selected planes through the depth of the sample [1,2]. A large number of studies have investigated the resolution of DHM and reported techniques for maximizing lateral and/or axial resolution by means of synthetic apertures, deconvolution, deep learning, multiplexing, or pixel sub-resolution techniques [3][4][5][6][7][8][9][10]. However, there has been little discussion of the limits of detectability of particles of different sizes and composition, i.e., the ability to accurately identify and measure the size of unresolved particles. ...
Off-axis digital holographic microscopy (DHM) provides both amplitude and phase images, and so it may be used for label-free 3D tracking of micro- and nano-sized particles of different compositions, including biological cells, strongly absorbing particles, and strongly scattering particles. Contrast is provided by differences in either the real or imaginary parts of the refractive index (phase contrast and absorption) and/or by scattering. While numerous studies have focused on phase contrast and improving resolution in DHM, particularly axial resolution, absent have been studies quantifying the limits of detection for unresolved particles. This limit has important implications for microbial detection, including in life-detection missions for space flight. Here we examine the limits of detection of nanosized particles as a function of particle optical properties, microscope optics (including camera well depth and substrate), and data processing techniques and find that DHM provides contrast in both amplitude and phase for unresolved spheres, in rough agreement with Mie theory scattering cross-sections. Amplitude reconstructions are more useful than phase for low-index spheres and should not be neglected in DHM analysis.
... The concept of the synthetic aperture was first applied to increase the resolution of the radio telescope and to synthetic aperture radar. [27,28] Later this concept was applied to improve the lateral resolution of optical imaging systems, [29][30][31][32][33] including optical coherence microscopy. [34,35] The synthetic aperture approach improves lateral resolution by extending the spectrum of collected lateral spatial frequencies, corresponding to a larger aperture in the spatial domain than the objective aperture of the imaging system. ...
A novel approach for image formation in optical coherence tomography (OCT) and microscopy is presented. The depth resolution of OCT, including recently developed nanosensitive OCT (nsOCT), is limited by the spectral bandwidth of the light source used for illumination. The proposed approach, synthetic OCT (synOCT), permits label‐free, depth‐resolved quantitative visualization of the subwavelength‐sized structures with nanosensitivity. Using synOCT it is possible to estimate the contribution of axial Fourier components of an object's structure in image formation at each small volume within the image. The size of such areas can be smaller than the resolution limit of the imaging system that provides potential for super‐resolution imaging. Visualization of the subwavelength periodic structures and quantitative visualization of the subwavelength internal structures of highly scattering biological samples, within voxels smaller than resolution limit of the imaging system, are demonstrated. In contrast to nsOCT, the trade‐off between spectral and spatial resolution is removed which results in dramatic improvement of both spectral and spatial resolution in synOCT relative to nsOCT.
... This requires costly ultraviolet (UV) optics in the experimental setup; also highly energetic UV photons are more prone towards photo-damage of the bio-samples. A synthetic aperture based DHM technique has been reported (Micó et al., 2008), where the passband limit of the imaging system is expanded by various ways and eventually provides better resolution. There are several structured illumination (Heintzmann and Huser, 2017; based techniques (Samanta et al., 2022(Samanta et al., , 2023 which are mainly developed for super-resolution fluorescent * Corresponding author. ...
... A few years later, Sato et al. applied a similar concept to validate a proto-platform for DHM [27] . This illumination strategy -usually termed as angular multiplexing by tilted beams -has a reach and successful curriculum to achieve SR imaging [ 5 , 28 ] in fields such as lithography [29][30][31] , tomography [32][33][34] , Fourier ptychographic microscopy (FPM) [35][36][37] and biomedical imaging [38][39][40][41][42] , just to cite some examples. ...
... The idea of this design is to have flexibility for SA shaping [ 39 , 76 ] depending on the used NA objective lens. Thus, it is possible to generate a full annulus of 8 shifted apertures surrounding the central one [38] or to generate a cross-shape aperture [ 41 , 77 ]. In our experimental validation, we have generated a four-leaf clover shape aperture to optimize the number of recordings but the designed illuminator can apply for objectives ranging from 5X to 10X depending on the pursued resolution gain factor. ...
... In our experimental validation, we have generated a four-leaf clover shape aperture to optimize the number of recordings but the designed illuminator can apply for objectives ranging from 5X to 10X depending on the pursued resolution gain factor. For instance, a threefold resolution improvement could in principle be achieved by using a 5 ×0.15NA objective and considering the 8 off-axis illuminations thus defining a contiguous -to the on-axis aperture -set of additional apertures having an annular shape with full 2D spatial-frequency domain coverage [38] . ...
Resolving power in imaging systems, optical microscopy in particular, is limited by several factors being diffraction probably the most important one. Digital holographic microscopy (DHM) allows diffraction-limited quantitative phase imaging (QPI) with high accuracy by retrieving complex fields using interferometric recording, and a bunch of superresolution (SR) techniques have been widely reported through the past. However, there are additional ways to retrieve the complex amplitude distribution (such as the transport of intensity equation – TIE), having additional advantages over interferometric recording. We present how to increase the resolution limit in low/medium numerical aperture (NA) microscope objectives by using time and angular multiplexing while providing quantitative phase imaging (QPI) retrieved by TIE algorithm. This is, to the best of our knowledge, the first time that the resolution limit is experimentally improved in combination with TIE for phase retrieval in QPI. The proposed approach is validated in a real microscope embodiment (Olympus IX81) using resolution targets for quantitative resolution analysis and verifying a resolution gain factor of 2 from an experimental point of view.
... 15 The recent development of automated data analysis and classification by artificial intelligence 16,17 exaggerates this everincreasing demand for high-resolution quantitative data. So far, the proposed approaches to QPI super-resolution are based on oblique illumination, 18,19 structured illumination, 20 and speckle illumination, 21,22 which, combined with post-processing, provide synthetic images with an effectively enlarged numerical aperture (NA). These synthetic aperture methods enhance resolving power by essentially multiplexing the spatial-frequency content of the object spectrum into an unused degree of freedom in the system, sacrificing acquisition speed, quantitative information accuracy, or a field of view (FOV). ...
Biomedical and metasurface researchers repeatedly reach for quantitative phase imaging (QPI) as their primary imaging technique due to its high-throughput, label-free, quantitative nature. So far, very little progress has been made towards achieving super-resolution in QPI. However, the possible super-resolving QPI would satisfy the need for quantitative observation of previously unresolved biological specimen features and allow unprecedented throughputs in the imaging of dielectric metasurfaces. Here we present a method capable of real-time super-resolution QPI, which we achieve by shaping the coherence gate in the holographic microscope with partially coherent illumination. Our approach is based on the fact that the point spread function (PSF) of such a system is a product of the diffraction-limited spot and the coherence-gating function (CGF) shaped similarly to the superoscillatory hotspot. The product simultaneously produces the PSF with a super-resolution central peak and minimizes sidelobe effects commonly devaluating the superoscillatory imaging. The minimization of sidelobes and resolution improvement co-occur in the entire field of view. Therefore, for the first time we achieve a single-shot widefield super-resolution QPI. We demonstrate here resolution improvement on simulated as well as experimental data. A phase resolution target imaging shows a resolving power improvement of 19%. Finally, we show the practical feasibility by applying the proposed method to the imaging of biological specimens.
... The reconstruction process is performed computer-driven numerically [12]. Since the DH technique was first proposed by Goodman and Lawrence, it has been successfully applied in a wide range of different applications such as surface contouring, particle analysis, microscopy, 3D information processing and etc. [12][13][14][15]. The purpose of digital holography is not just to retrieve 3D information. ...
... MSE, MAE, PSNR and SSIM metrics are used to evaluate the quality of the reconstructed images in this work. The mathematical expressions for MSE, MAE, PSNR and SSIM are defined in (13), respectively: ...
... The expressions given in (13) are defined in Table 5. Table 5 The definitions in (13). ...
World Health Organization has described the real-time reverse transcription-polymerase chain reaction test method for the diagnosis of the novel coronavirus disease (COVID-19). However, the limited number of test kits, the long-term results of the tests, the high probability of the disease spreading during the test and imaging without focused images necessitate the use of alternative diagnostic methods such as chest X-ray (CXR) imaging. The storage of data obtained for the diagnosis of the disease also poses a major problem. This causes misdiagnosis and delays treatment. In this work, we propose a hybrid 3D reconstruction method of CXR images (CXRI) to detect coronavirus pneumonia and prevent misdiagnosis on CXRI. We used the digital holography technique (DHT) for obtaining a priori information of CXRI stored in created digital hologram (CDH). In this way, the elimination of the storage problem that requires high space was revealed. In addition, Discrete Orthonormal S-Transform (DOST) is applied to the reconstructed CDH image obtained by using DHT. This method is called CDH_DHT_DOST. A multiresolution spatial-frequency representation of the lung images that belong to healthy people and diseased people with the COVID-19 virus is obtained by using the CDH_DHT_DOST. Moreover, the genetic algorithm (GA) is adopted for the reconstruction process for optimization of the CDH image and then DOST is applied. This hybrid method is called CDH_GA_DOST. Finally, we compare the results obtained from CDH_DHT_DOST and CDH_GA_DOST. The results show the feasibility of reconstructing CXRI with CDH_GA_DOST. The proposed method holds promises to meet demands for the detection of the COVID-19 virus.
... Many QPI methods achieve subdiffraction limited resolution by a sequential oblique coherent beam illumination and holographic detection. [8][9][10][11] These methods acquire images with downshifted high-frequency components of the object spectrum and digitally synthesize a larger system aperture. A similar principle also applies to structured illumination microscopy in coherent modalities such as QPI, which illuminates the specimen simultaneously by several oblique beams. ...
Quantitative phase imaging (QPI) has quickly established its role in identifying rare events and screening in biomedicine or automated image data analysis using artificial intelligence. These and many other applications share the requirement for extensive high-quality datasets, which is challenging to meet because the invariance of the space–bandwidth product (SBP) fundamentally limits the microscope system throughput. Here, we present a method to overcome the SBP limit by achieving QPI super-resolution using a synthetic aperture approach in a holographic microscope with a partially coherent broad source illumination. We exploit intrinsic coherence-gating properties of the partially coherent light combined with the oblique illumination provided by the diffraction on a simple phase grating placed in proximity of the specimen. We sequentially coherence gate the light scattered into each grating’s diffraction order, and we use the acquired images to synthesize QPI with significantly increased spatial frequency bandwidth. The resolution of QPI is increased substantially beyond Abbe’s diffraction limit while a large field of view of low numerical aperture objectives is kept. This paper presents a thorough theoretical treatment of the coherence-gated imaging process supplemented by a detailed measurement methodology. The capability of the proposed method is demonstrated by imaging a phase resolution target and biological specimens. We envision our work providing an easily implementable super-resolution QPI method particularly suitable for high-throughput biomedical applications.
... Digital holographic microscopy (DHM) is a simple, noninvasive, and non-destructive optical technique with actual and potential applications in diverse research fields [1]. During the past years, DHM has proven to be a powerful tool for measuring very small deformations or displacements [2], vibrations [3], refractive indices [4,5], surface morphology and 3D shape [6,7], thermal variations in fluids [8,9], tracking particles [10,11], and measurements of biological samples [12][13][14], to mention a few examples. DHM exploits the advantages of digital holography regarding 3D information (amplitude + phase) with the lateral resolution of conventional optical microscopy (≈1 µm), i.e., at the so-called diffraction limit [15]. ...
... For this reason, we tested the performance of the holographic setup with a relatively simple system, whose reconstructed phase was quite predictable. By implementing Eq. (6) for each matrix element of the obtained ϕ, we could reconstruct a 3D height map of features on the sample surface. The results are shown in Fig. 4(a). ...
We report the implementation of lensless off-axis digital holographic microscopy as a non-destructive optical analyzer for nano-scale structures. The measurement capacity of the system was validated by analyzing the topography of a metallic grid with ${\approx} 150\;{\rm{nm}}$ ≈ 150 n m thick opaque features. In addition, an experimental configuration of self-reference was included to study the dynamics of the capillary filling phenomena in nanostructured porous silicon. The fluid front position as a function of time was extracted from the holograms, and the typical square root of time kinematics was recovered. The results shown are in agreement with previous works on capillary imbibition in similar structures and confirm a first step towards unifying holographic methods with fluid dynamics theory to develop a spatially resolved capillary tomography system for nanoporous materials characterization.
... Mico et al. utilized a vertical-cavity surface-emitting laser (VCSEL) array to generate multi-directional oblique illumination of DHM and retained a resolution gain with a factor of five 47 . The use of scanning elements has also been reported as a technological improvement for providing more flexible oblique beam illumination 28,33,37,51 , which has also been validated 29,31,52 in comparison with the tilting of the illumination direction. For instance, Cheng et al. used a 2D Galvo-scanner to generate oblique illumination for DHM ( Fig. 3b), achieving a two-fold isotropic resolution enhancement. ...
... Oblique beam illumination techniques have recently been implemented in a commercial upright Olympus microscope 39 . Notably, the maximum synthetic numerical aperture is limited by NA<1 in imaging systems with dry objectives, and further resolution improvements to λ/3.7 were demonstrated using evanescent waves 29 . In addition, axial rather than transversal resolution improvement has also been validated by SA generation 61 , and an application of the technique to edge processing was also reported 62 . ...
