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Dielectric tensor tomography reconstructs the three-dimensional dielectric tensors of microscopic objects and provides information about the crystalline structure orientations and principal refractive indices. Because dielectric tensor tomography is based on transmission measurement, it suffers from the missing cone problem, which causes poor axial resolution, underestimation of the refractive index, and halo artifacts. In this study, we study the application of total variation and positive semi-definiteness regularization to three-dimensional tensor distributions. In particular, we demonstrate the reduction of artifacts when applied to dielectric tensor tomography.

This study investigates key country-level economic factors that influence listed real estate investment trust (REIT) market capitalization across 23 countries that currently operate active REIT mar...

Dielectric tensor tomography (DTT) enables the reconstruction of three-dimensional (3D) dielectric tensors, which provides a physical measure of 3D optical anisotropy. Herein, we present a cost-effective and robust method for DTT measurement using a multiplexing approach. By exploiting two orthogonally polarized reference beams with different angles in an off-axis interferometer, two polarization-sensitive interferograms were overlapped and recorded using a single camera. Then, the two multiplexed interferograms were separated in the Fourier domain, enabling the reconstruction of polarization-sensitive fields. Finally, by measuring the polarization-sensitive fields for various illumination angles, 3D dielectric tensor tomograms were reconstructed. The proposed method was experimentally demonstrated by reconstructing the 3D dielectric tensors of various liquid crystal particles with radial and bipolar orientational configurations.

This study aims to bridge the gap between two perspectives of explainability−machine learning and engineering, and economics and standard econometrics−by applying three marginal measurements. The existing real estate literature has primarily used econometric models to analyze the factors that affect the default risk of mortgage loans. However, in this study, we estimate a default risk model using a machine learning-based approach with the help of a U.S. securitized mortgage loan database. Moreover, we compare the economic explainability of the models by calculating the marginal effect and marginal importance of individual risk factors using both econometric and machine learning approaches. Machine learning-based models are quite effective in terms of predictive power; however, the general perception is that they do not efficiently explain the causal relationships within them. This study utilizes the concepts of marginal effects and marginal importance to compare the explanatory power of individual input variables in various models. This can simultaneously help improve the explainability of machine learning techniques and enhance the performance of standard econometric methods.

Histopathology relies upon the staining and sectioning of biological tissues, which can be laborious and may cause artefacts and distort tissues. Here, we demonstrate label-free volumetric imaging of thick-tissue slides, exploiting refractive index distributions as intrinsic imaging contrast. The present method systematically exploits label-free quantitative phase imaging techniques, volumetric reconstruction of intrinsic refractive index distributions in tissues, and numerical algorithms for the seamless stitching of multiple 3D tomograms and for reducing scattering-induced image distortion. We demonstrate demonstrated label-free volumetric imaging of thick tissues with the field of view of 2 mm × 1.75 mm × 0.2 mm with a spatial resolution of 170 nm × 170 nm × 1200 nm. The number of optical modes, calculated as the reconstructed volume divided by the size of the point spread function, was approximately 20 Giga voxels. We have also demonstrated that different tumour types, and a variety of precursor lesions and pathologies can be visualized with the present method.Abstract Figure

The dielectric tensor is a physical descriptor of fundamental light-matter interactions, characterizing anisotropic materials with principal refractive indices and optic axes. Despite its importance in scientific and industrial applications ranging from material science to soft matter physics, the direct measurement of the three-dimensional dielectric tensor has been limited by the vectorial and inhomogeneous nature of light scattering from anisotropic materials. Here, we present a dielectric tensor tomographic approach to directly measure dielectric tensors of anisotropic structures including the spatial variations of principal refractive indices and directors. The anisotropic structure is illuminated with a polarized plane wave with various angles and polarization states. Then, the scattered fields are holographically measured and converted into vectorial diffracted field components. Finally, by inversely solving a vectorial wave equation, the three-dimensional dielectric tensor is reconstructed. Using this approach, we demonstrate quantitative tomographic measurements of various nematic liquid-crystal structures and their fast three-dimensional non-equilibrium dynamics.

We realized multiscale label-free volumetric histopathology of thick-tissue slides. The present method exploits label-free volumetric reconstruction of intrinsic refractive index distributions in tissues, and numerical algorithms for seamless stitching and reduction of scattering-induced image distortion.

Optical diffraction tomography (ODT) is a label-free three-dimensional (3D) microscopy technique allowing to retrieve the refractive-index distributions of optically translucent samples. Until recently, the histopathological applications of ODT have been impeded by the difficulty of imaging thick and wide tissues. Here, we demonstrate rapid, wide-field 3D ODT for imaging biological tissues. We designed a high-speed stitching ODT platform exploiting a digital micromirror device and a motorized stage. Developing a fast algorithmic framework that relieves the stitching artifacts and contrast loss due to multiple scattering, we demonstrate high-contrast 3D imaging of 100-m-thick, square-millimeter-wide pathological tissues at sub-micrometer resolution.

In this paper, an 11-bit ring amplifier (RAMP) pipeline ADC with settling-time improvement scheme is proposed. A RAMP-based ADC is adopted to achieve the reduced current consumption and hardware area. Novel technique utilizing the highpass filter is incorporated to improve the settling time of the amplifier. Each stage consists of a 1.5-bit multiplying digital-to-analog (MDAC) and flash ADC (FADC) since the unity-gain frequency of RAMP is affected by the load of MDAC. The conventional sample and hold amplifier (SHA) is used instead of RAMP in order to relieve the nonlinear distortion at the first stage. The pipelined ADC is designed in a 65nm CMOS process. For a single supply voltage of 1.2V, total current consumption is 15.5mA. At the sampling rate of 100MS/sec, SNDR and ENOB are 66.83dB and 10.81bits, respectively.

We investigated the in-situ photothermal response of human red blood cells (RBCs) by combining photothermal heat generation and 3D quantitative phase imaging techniques. Gold-nanorod-coated substrates were excited using near-infrared light to generate local heat to RBCs, and response was measured by imaging 3-D refractive index tomograms of cells under various near infrared (NIR) excitation conditions. On photothermal treatment, cell morphology changed from discoid to crescent shapes, cell volume and dry mass decreased, and hemoglobin concentration increased. We also investigated the irreversible deformation of RBCs when multiple intense excitation shocks are applied. These results provide a new understanding of thermodynamic aspects of cell biology and hematology. O_FIG_DISPLAY_L [Figure 1] M_FIG_DISPLAY C_FIG_DISPLAY

Intact optical information of an object delivered through an imaging system is deteriorated by imperfect optical elements and unwanted defects. Image deconvolution has been widely exploited as a recovery technique due to its practical feasibility, and operates by assuming linear shift-invariant property of the imaging system. However, shift invariance does not rigorously hold in all imaging situations and is not a necessary condition for solving an inverse problem of light propagation. Several improved deconvolution techniques exploiting spatially variant point spread functions have been proposed in previous studies. However, the full characterization of an optical imaging system for compensating aberrations has not been considered. Here, we present a generalized method to solve the linear inverse problem of coherent light propagations without any regularization method or constraint on shift invariance by fully measuring the transmission matrix of the imaging system. Our results show that severe aberrations produced by a tilted lens or an inserted disordered layer can be corrected properly only by the proposed generalized image deconvolution. This work generalizes the theory of image deconvolution, and enables distortion-free imaging under general imaging condition.

Measurement and control of a microscopic system's temperature distribution are increasingly important in diverse applications, yet measuring a three-dimensional (3D) temperature distribution at the microscale has remained out of reach. Here researchers use quantitative phase imaging to measure microscopically the 3D refractive-index distribution of a medium, from which its 3D temperature distribution is retrieved. This approach can facilitate our understanding of various thermal phenomena and applications spanning nanotechnology, bioengineering, and the semiconductor industry.

Optical diffraction tomography (ODT), which is one of the 3-D imaging techniques, enables non-invasive, label-free, and quantitative imaging of microscopic particles by retrieving multiple optical fields and reconstructing the 3-D hologram image of a sample. However, ODT employing the illumination scanning method suffers from poor axial resolution. In order to remedy this problem, we introduce TOmographic MOuld for optical TRAPping (TOMOTRAP) in ODT, which can control the orientation and shape of arbitrarily shaped dielectric objects. From optical field images of a sample rotated by several angles via TOMOTRAP, we reconstruct the 3-D RI distributions of samples with isotropic spatial resolution.

In coherent imaging systems, parasitic fringes and concentric patterns could commonly be found due to the unwanted multiple reflections [1]. One fundamental solution for the coherent noise is to use a temporally incoherent light source. However, maintaining the full-field interference fringe contrast using temporally incoherent light is not straightforward for interferometric imaging techniques such as quantitative phase imaging (QPI). Fortunately, several brilliant incoherent QPI techniques have been realized for wide-field imaging mainly through the common-path interferometer geometries [2-4]. However, it has been more difficult to implement incoherent-light-based optical diffraction tomography (ODT) due to the additional angle-scanning illumination unit that induces severe decoherence over the camera field-of-view [5]. Here, we suggest a temporally low-coherence optical diffraction tomography by angle-scanning broadband illumination based on general Mach-Zehnder interferometric geometry. We have designed an angle-scanning unit composed of two digital micromirror devices (DMDs) to maintain interference fringe contrast across the whole field of view during the angle-scanning sequence. Further, we have developed the theoretical framework for ODT reconstruction using incoherent light. In the light of our recent developments, we will discuss the theoretical and practical constraints, and suggest the best degree of incoherency for incoherent ODT. We will also demonstrate the incoherent optical diffraction tomography of plastic microspheres, human blood cells and rat pheochromocytoma cells. References 1. I. Choi, K. Lee, and Y. Park, "Compensation of aberration in quantitative phase imaging using lateral shifting and spiral phase integration," Opt. Express 25, 30771-30779 (2017). 2. Z. Wang, L. Millet, M. Mir, H. Ding, S. Unarunotai, J. Rogers, M. U. Gillette, and G. Popescu, "Spatial light interference microscopy (SLIM)," Opt. Express 19, 1016-1026 (2011). 3. B. Bhaduri, H. Pham, M. Mir, and G. Popescu, "Diffraction phase microscopy with white light," Opt. Lett. 37, 1094-1096 (2012). 4. Y. Baek, K. Lee, J. Yoon, K. Kim, and Y. Park, "White-light quantitative phase imaging unit," Opt. Express 24, 9308-9315 (2016). 5. M. Rinehart, Y. Zhu, and A. Wax, "Quantitative phase spectroscopy," Biomed. Opt. Express 3, 958-965 (2012).

© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Temporally low-coherent optical diffraction tomography (ODT) is proposed and demonstrated based on angle-scanning Mach-Zehnder interferometry. Using a digital micromirror device based on diffractive tilting, the full-field interference of incoherent light is successfully maintained during every angle-scanning sequences. Further, current ODT reconstruction principles for temporally incoherent illuminations are thoroughly reviewed and developed. Several limitations of incoherent illumination are also discussed, such as the nondispersive assumption, optical sectioning capacity and illumination angle limitation. Using the proposed setup and reconstruction algorithms, low-coherent ODT imaging of plastic microspheres, human red blood cells and rat pheochromocytoma cells is experimentally demonstrated.

Optical diffraction tomography (ODT) enables the reconstruction of the three-dimensional (3D) refractive-index (RI) distribution of a biological cell, which provides invaluable information for cellular and subcellular structures in a non-invasive manner. However, ODT suffers from an inferior axial resolution, due to the limited accessible angles imposed by the numerical aperture of the objective lens. In this study, we propose and experimentally demonstrate an approach to enhance the 3D reconstruction performance in ODT. By employing trapezoidal micromirrors, side scattered signals from the sample are measured for various side plane-wave-illumination angles. By combining the side scattered fields with the forward scattered fields, the axial resolution and 3D image quality of ODT are improved, without changing optical instruments. The feasibility and applicability of the proposed method are demonstrated by reconstructing the 3D RI distribution of a red blood cell and HeLa cells in hydrogel. We also present systematic analyses of the improved 3D imaging performance using numerical simulations and experimental measurements for the 3D transfer function, a point object, and a microsphere. The analyses demonstrate an improved axial resolution of 0.31 μm, 4.8 times smaller than that of the conventional method. The proposed method enables the non-invasive and accurate 3D imaging of 3D cultured cells, which is crucial for cell biology studies.

The measurement of three-dimensional (3D) images and the analysis of subcellular organelles are crucial for the study of the pathophysiology of cells and tissues. Optical diffraction tomography (ODT) facilitates label-free and quantitative imaging of live cells by reconstructing 3D refractive index (RI) distributions. In many cases, however, the contrast in RI distributions is not strong enough to effectively distinguish subcellular organelles in live cells. To realize label-free and quantitative imaging of subcellular organelles in unlabeled live cells with enhanced contrasts, we present a computational approach using ODT. We demonstrate that the contrast of ODT can be enhanced via spatial high-pass filtering in a 3D spatial frequency domain, and that it yields theoretically equivalent results to physical dark-field illumination. Without changing the optical instruments used in ODT, subcellular organelles in live cells are clearly distinguished by applying a simple but effective computational approach that is validated by comparison with 3D epifluorescence images. We expect that the proposed method will satisfy the demand for label-free organelle observations, and will be extended to fully utilize complex information in 3D RI distributions.

Quantitative phase imaging (QPI) has emerged as one of the powerful imaging tools for the study of live cells in a non-invasive manner. In particular, multimodal approaches combining QPI and fluorescence microscopic techniques have been recently developed for superior spatiotemporal resolution as well as high molecular specificity. In this review, we briefly summarize recent advances in three-dimensional QPI combined with fluorescence techniques for the correlative study of cell pathophysiology. Through this review, biologists and clinicians can be provided with insights on this rapidly growing field of research and may find broader applications to investigate unrevealed nature in cell physiology and related diseases.

Microalgae are promising candidates for biofuel production due to their high lipid content. To facilitate utilization of the microalgae for biofuel, rapid quantification of the lipid contents in microalgae is necessary. However, conventional methods based on the chemical extraction of lipids require a time-consuming destructive extraction process. Here, we demonstrate label-free, non-invasive, rapid quantification of the lipid contents in individual micro-algal cells measuring the three-dimensional refractive index tomograms. We measure three-dimensional refractive index distributions within Nannochloropsis oculata cells and find that lipid droplets are identifiable in tomograms by their high refractive index. In addition, we alter N. oculata under nitrogen deficiency by measuring the volume, lipid weight, and dry cell weight of individual cells. Characterization of individual cells allows correlative analysis between the lipid content and size of individual cells.

The structure of pollen grains is related to the reproductive function of the plants. Here, three-dimensional (3D) refractive index maps were obtained for individual conifer pollen grains using optical diffraction tomography (ODT). The 3D morphological features of pollen grains from pine trees were investigated using measured refractive index maps, in which distinct substructures were clearly distinguished and analyzed. Morphological and physiochemical parameters of the pollen grains were quantified from the obtained refractive index (RI) maps and used to quantitatively study the interspecific differences of pollen grains from different strains. Our results demonstrate that ODT can assess the structure of pollen grains. This label-free and rapid 3D imaging approach may provide a new platform for understanding the physiology of pollen grains.

We propose and experimentally demonstrate a method of polarization-sensitive quantitative phase imaging using two photodetectors and a digital micromirror device. Instead of recording wide-field interference patterns, finding the modulation patterns maximizing focused intensities in terms of the polarization states enables polarization-dependent quantitative phase imaging without the need for a reference beam and an image sensor. The feasibility of the present method is experimentally validated by reconstructing Jones matrices of several samples including a polystyrene microsphere, a maize starch granule, and a mouse retinal nerve fiber layer. Since the present method is simple and sufficiently general, we expect that it may offer solutions for quantitative phase imaging of birefringent materials.

We present a multimodal approach for measuring the three-dimensional (3D) refractive index (RI) and fluorescence distributions of live cells by combining optical diffraction tomography (ODT) and 3D structured illumination microscopy (SIM). A digital micromirror device is utilized to generate structured illumination patterns for both ODT and SIM, which enables fast and stable measurements. To verify its feasibility and applicability, the proposed method is used to measure the 3D RI distribution and 3D fluorescence image of various samples, including a cluster of fluorescent beads, and the time-lapse 3D RI dynamics of fluorescent beads inside a HeLa cell, from which the trajectory of the beads in the HeLa cell is analyzed using spatiotemporal correlations.

SummaryThe structure of pollen grains is related to the reproductive function of the plants. Here, three-dimensional (3D) refractive index maps were obtained for individual conifer pollen grains using optical diffraction tomography (ODT).The 3D morphological features of pollen grains from pine trees were investigated using measured refractive index maps, in which distinct substructures were clearly distinguished and analyzed.Morphological and physiochemical parameters of the pollen grains were quantified from the obtained refractive index (RI) maps and used to quantitatively study the interspecific differences of pollen grains from different strains.Our results demonstrate that ODT can assess the structure of pollen grains. This label-free and rapid 3D imaging approach may provide a new platform for understanding the physiology of pollen grains.

Optical diffraction tomography (ODT) provides three-dimensional refractive index (RI) tomograms of a transparent microscopic object. However, because of the finite numerical aperture of objective lenses, ODT has a limited access to diffracted light and suffers from poor spatial resolution, particularly along the axial direction. To overcome the limitation of the quality of RI tomography, we present an algorithm that accurately reconstructs RI tomography of a specimen with discrete and uniform RI, using prior information about the RI levels. Through simulations and experiments on various samples, including microspheres, red blood cells, and water droplets, we show that the proposed method can precisely reconstruct RI tomograms of samples which have discrete and homogenous RI distributions in the presence of the missing information and noise.

We propose a multimodal optical system combining ODT and 3-D SIM to measure both 3-D RI and fluorescence distribution of a sample with high spatiotemporal resolution as well as molecular specificity.

We present a method of reference-free single-point holographic imaging by exploiting the time-reversal nature of optical phase conjugation, without the need for an image sensor and a reference beam.

Microfluidic mixing plays a key role in various fields, including biomedicine and chemical engineering. To date, although various approaches for imaging microfluidic mixing have been proposed, they provide only quantitative imaging capability and require for exogenous labeling agents. Quantitative phase imaging techniques, however, circumvent these problems and offer label-free quantitative information about concentration maps of microfluidic mixing. We present the quantitative phase imaging of microfluidic mixing in various types of PDMS microfluidic channels with different geometries; the feasibility of the present method was validated by comparing it with the results obtained by theoretical calculation based on Fick’s law.

Optical diffraction tomography (ODT) has been an emerging optical technique for label-free imaging of three-dimensional (3-D) refractive index (RI) distribution of biological samples. ODT employs interferometric microscopy for measuring multiple holograms of samples with various incident angles, from which the Fourier diffraction theorem reconstructs the 3-D RI distribution of samples from retrieved complex optical fields. Since the RI value is linearly proportional to the protein concentration of biological samples where the proportional coefficient is called as refractive index increment (RII), reconstructed 3-D RI tomograms provide precise structural and biochemical information of individual biological samples. Because most proteins have similar RII value, however, ODT has limited molecular specificity, especially for imaging eukaryotic cells having various types of proteins and subcellular organelles. Here, we present an ODT system combined with structured illumination microscopy which can measure the 3-D RI distribution of biological samples as well as 3-D super-resolution fluorescent images in the same optical setup. A digital micromirror device (DMD) controls the incident angle of the illumination beam for tomogram reconstruction, and the same DMD modulates the structured illumination pattern of the excitation beam for super-resolution fluorescent imaging. We first validate the proposed method for simultaneous optical diffraction tomographic imaging and super-resolution fluorescent imaging of fluorescent beads. The proposed method is also exploited for various biological samples.

One of the fundamental limitations in photonics is the lack of a bidirectional transducer that can convert optical information into electronic signals or vice versa. In acoustics or at microwave frequencies, wave signals can be simultaneously measured and modulated by a single transducer. In optics, however, optical fields are generally measured via reference-based interferometry or holography using silicone-based image sensors, whereas they are modulated using spatial light modulators. Here, we propose a scheme for an optical bidirectional transducer using a spatial light modulator. By exploiting the principle of time-reversal symmetry of light scattering, two-dimensional reference-free measurement and modulation of optical fields are realized. We experimentally demonstrate the optical bidirectional transducer for optical information consisting of 128 x 128 spatial modes at visible and short-wave infrared wavelengths.

The properties of income-to-price ratios in asset markets have potentially far reaching implications for understanding investor behavior. Prevailing levels of commercial real estate (CRE) capitalization rates, similar to price/earnings ratios for stocks and owner equivalent rent-to-price relatives for houses, may foretell future investment returns and income growth rates. In CRE capitalization rate models, rent growth rates often proxy for the net operating income (NOI) growth rates. Empirical studies of capitalization rate predictive powers produce inconsistent results that may be due either to the use of these rent growth proxies, model misspecification, or both. We use a novel approach for generating NOI growth rate estimates that involves combining survey rent and the expense growth rates for U.S. apartments. Our GARCH analysis of the capitalization rate spread process using the estimated NOI growth rate produces theoretically consistent results. Importantly, we demonstrate efficiency gains from using...

Modern optical imaging possesses a huge information capacity whose corresponding space-bandwidth product (SBP) reaches tens of megapixels. However, despite the advances in optical and electronic devices, the SBP of an optical microscope is greatly limited, resulting in a reduced field of view or resolution of an image. In this paper, we exploit the Kramers–Kronig relations in digital holography to achieve high SBP imaging, demonstrating a complex amplitude image that can surpass the SBP of a bright-field image. The capability of the proposed method is demonstrated by imaging static samples and biological tissues. We successfully measure a 4.2-megapixel complex amplitude image whose bright-field counterpart exhibits 16.7 megapixels.