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1. Single-pixel fluorescent diffraction tomography

   https://doi.org/10.1364/OPTICA.400547  

   Stockton, Patrick_A; Field, Jeffrey_J; Squier, Jeff; Pezeshki, Ali; Bartels, Randy_A (November 2020, Optica)

   Optical diffraction tomography (ODT) is an indispensable tool for studying objects in three dimensions. Until now, ODT has been limited to coherent light because spatial phase information is required to solve the inverse scattering problem. We introduce a method that enables ODT to be applied to imaging incoherent contrast mechanisms such as fluorescent emission. Our strategy mimics the coherent scattering process with two spatially coherent illumination beams. The interferometric illumination pattern encodes spatial phase in temporal variations of the fluorescent emission, thereby allowing incoherent fluorescent emission to mimic the behavior of coherent illumination. The temporal variations permit recovery of the spatial distribution of fluorescent emission with an inverse scattering model. Simulations and experiments demonstrate isotropic resolution in the 3D reconstruction of a fluorescent object. 

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2. Spatial light interference microscopy: principle and applications to biomedicine

   https://doi.org/10.1364/AOP.417837  

   Chen, Xi; Kandel, Mikhail_E; Popescu, Gabriel (May 2021, Advances in Optics and Photonics)

   In this paper, we review spatial light interference microscopy (SLIM), a common-path, phase-shifting interferometer, built onto a phase-contrast microscope, with white-light illumination. As one of the most sensitive quantitative phase imaging (QPI) methods, SLIM allows for speckle-free phase reconstruction with sub-nanometer path-length stability. We first review image formation in QPI, scattering, and full-field methods. Then, we outline SLIM imaging from theory and instrumentation to diffraction tomography. Zernike’s phase-contrast microscopy, phase retrieval in SLIM, and halo removal algorithms are discussed. Next, we discuss the requirements for operation, with a focus on software developed in-house for SLIM that enables high-throughput acquisition, whole slide scanning, mosaic tile registration, and imaging with a color camera. We introduce two methods for solving the inverse problem using SLIM, white-light tomography, and Wolf phase tomography. Lastly, we review the applications of SLIM in basic science and clinical studies. SLIM can study cell dynamics, cell growth and proliferation, cell migration, mass transport, etc. In clinical settings, SLIM can assist with cancer studies, reproductive technology, blood testing, etc. Finally, we review an emerging trend, where SLIM imaging in conjunction with artificial intelligence brings computational specificity and, in turn, offers new solutions to outstanding challenges in cell biology and pathology. 

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3. Quantitative 3D refractive index tomography of opaque samples in epi-mode

   https://doi.org/10.1364/OPTICA.410135  

   Ledwig, Patrick; Robles, Francisco_E (December 2020, Optica)

   Three-dimensional (3D) refractive index (RI) tomography has recently become an exciting new tool for biological studies. However, its limitation to (1) thin samples resulting from a need of transmissive illumination and (2) small fields of view (typically $\sim <\#comment/>50\text{µ<\#comment/>}\mathrm{m}\times <\#comment/>50\text{µ<\#comment/>}\mathrm{m}$) has hindered its utility in broader biomedical applications. In this work, we demonstrate 3D RI tomography with a large field of view in opaque, arbitrarily thick scattering samples (unsuitable for imaging with conventional transmissive tomographic techniques) with a penetration depth of ca. one mean free scattering path length ( $\sim <\#comment/>100\text{µ<\#comment/>}\mathrm{m}$in tissue) using a simple, low-cost microscope system with epi-illumination. This approach leverages a solution to the inverse scattering problem via the general non-paraxial 3D optical transfer function of our quantitative oblique back-illumination microscopy (qOBM) optical system. A theoretical analysis is presented along with simulations and experimental validations using polystyrene beads, and rat and human thick brain tissues. This work has significant implications for the investigation of optically thick, semi-infinite samples in a non-invasive and label-free manner. This unique 3D qOBM approach can extend the utility of 3D RI tomography for translational and clinical medicine. 

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4. Grain-Scale Stress Heterogeneity in Concrete from In-Situ X-Ray Measurements

   https://doi.org/10.2139/ssrn.5025153  

   Thakur, Mohmad Mohsin; Henningsson, Axel; Engqvist, Jonas; Pierre, Olivier Autran; Wright, J; Hurley, Ryan (November 2024, SSRN)

   Concrete features significant microstructural heterogeneity which affects its mechanical behavior. Strain localization in the matrix phase of concrete has received significant attention due to its relation to microcracking and our ability to quantify it with X-ray computed tomography (XRCT). In contrast, stresses in sand and aggregates remain largely unmeasured but remain critical for micromechanics-based theories of failure. Here, we use a combination of in-situ XRCT, 3D X-ray diffraction (3DXRD), and scanning 3DXRD to directly measure strain and stress within sand grains in two samples of mortar containing different sand volume fractions. Our results reveal that, in contrast to inclusion theories from continuum micromechanics, aggregates feature a broad distribution of average stresses and significant gradients in their internal stress fields. Our work furnishes the first known dataset with these quantitative stress measurements and motivates improvements in micromechanics models for concrete which can capture stress heterogeneity. 

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5. Time-of-Flight Quantum Tomography of Single Atom Motion

   https://doi.org/10.48550/arXiv.2203.03053  

   Brown, M.O.; Muleady, S.R.; Dworschack, W.J.; Lewis-Swan, R.J.; Rey, A.M.; Romero-Isart, O; Regal, C.A. (July 2022, ArXivorg)

   Time of flight is an intuitive way to determine the velocity of particles and lies at the heart of many capabilities ranging from mass spectrometry to fluid flow measurements. Here we show time-of-flight imaging can realize tomography of a quantum state of motion of a single trapped atom. Tomography of motion requires studying the phase space spanned by both position and momentum. By combining time-of-flight imaging with coherent evolution of the atom in an optical tweezer trap, we are able to access arbitrary quadratures in phase space without relying on coupling to a spin degree of freedom. To create non-classical motional states, we harness quantum tunneling in the versatile potential landscape of optical tweezers, and our tomography both demonstrates Wigner function negativity and assesses coherence of non-stationary states. Our demonstrated tomography concept has wide applicability to a range of particles and will enable characterization of non-classical states of more complex systems or massive dielectric particles. 

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