Label-Free Three-Dimensional Morphological Characterization of Cell Death Using Holographic Tomography.

This study presents a novel label-free approach for characterizing cell death states, eliminating the need for complex molecular labeling that may yield artificial or ambiguous results due to technical limitations in microscope resolution. The proposed holographic tomography technique offers a label-free avenue for capturing precise three-dimensional (3D) refractive index morphologies of cells and directly analyzing cellular parameters like area, height, volume, and nucleus/cytoplasm ratio within the 3D cellular model. We showcase holographic tomography results illustrating various cell death types and elucidate distinctive refractive index correlations with specific cell morphologies complemented by biochemical assays to verify cell death states. These findings hold promise for advancing in situ single cell state identification and diagnosis applications.

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.

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

This feature issue is a continuation of a tradition to follow the conclusion of the Optica Topical Meeting on Digital Holography and 3D Imaging (DH+3D). It addresses current research topics in digital holography and 3D imaging that are also in line with the topics of Applied Optics and Journal of the Optical Society of America A.

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

This feature issue is a continuation of a tradition to follow the conclusion of the Optica Topical Meeting on Digital Holography and 3D Imaging (DH+3D). It addresses current research topics in digital holography and 3D imaging that are also in line with the topics of Applied Optics and Journal of the Optical Society of America A.

Influence of Yokukansan on the refractive index of neuroblastoma cells.

Yokukansan (YKS) is a traditional Japanese herbal medicine that is increasingly being studied for its effects on neurodegenerative diseases. In our study, we presented a novel methodology for a multimodal analysis of the effects of YKS on nerve cells. The measurements of 3D refractive index distribution and its changes performed by holographic tomography were supported with an investigation by Raman micro-spectroscopy and fluorescence microscopy to gather complementary morphological and chemical information about cells and YKS influence. It was shown that at the concentrations tested, YKS inhibits proliferation, possibly involving reactive oxygen species. Also substantial changes in the cell RI after few hours of YKS exposure were detected, followed by longer-term changes in cell lipid composition and chromatin state.

Investigation of Nonlinear Optical Properties of Quantum Dots Deposited onto a Sample Glass Using Time-Resolved Inline Digital Holography.

We report on the application of time-resolved inline digital holography in the study of the nonlinear optical properties of quantum dots deposited onto sample glass. The Fresnel diffraction patterns of the probe pulse due to noncollinear degenerate phase modulation induced by a femtosecond pump pulse were extracted from the set of inline digital holograms and analyzed. The absolute values of the nonlinear refractive index of both the sample glass substrate and the deposited layer of quantum dots were evaluated using the proposed technique. To characterize the inhomogeneous distribution of the samples' nonlinear optical properties, we proposed plotting an optical nonlinearity map calculated as a local standard deviation of the diffraction pattern intensities induced by noncollinear degenerate phase modulation.

Roadmap on Digital Holography-Based Quantitative Phase Imaging.

Quantitative Phase Imaging (QPI) provides unique means for the imaging of biological or technical microstructures, merging beneficial features identified with microscopy, interferometry, holography, and numerical computations. This roadmap article reviews several digital holography-based QPI approaches developed by prominent research groups. It also briefly discusses the present and future perspectives of 2D and 3D QPI research based on digital holographic microscopy, holographic tomography, and their applications.

Application of digital holographic tomography in antitumor effect of cantharides complex on 4T1 breast cancer cells.

The study focuses on a methodology providing noninvasive monitoring and evaluation of the antitumor effect of traditional Chinese medicine, cantharides complex (canth), on 4T1 breast tumor cells. Digital holographic tomography (DHT) and developed data post-processing algorithms were used for quantitative estimation of changes in optical and morphological parameters of cells. We calculated and compared data on the refractive index, thickness, and projected area of 4T1 breast tumor cells in control untreated specimens and those treated with doxorubicin hydrochloride (DOX), canth, and their combinations. Post-treatment changes in cellular morphology recorded by DHT demonstrated that the two drugs led to noticeably different morphological changes in cells that can be presumably associated with different pathways of their death, apoptosis, or necrosis. The effect of combined treatment with these two drugs strongly depended on their relative concentrations and could lead to changes characteristic either for DOX or for canth; however, being more profound than those obtained when using each drug solely. The results obtained by DHT are in a good correspondence with commonly used cell viability analysis and immunofluorescent analysis of changes in cellular cytoskeleton.

Noncollinear degenerate phase modulation in samples with inhomogeneous optical nonlinear properties [Invited].

Digital inline pump-probe holography can be applied to estimate parameters of samples' optical nonlinear properties. Here we propose a mathematical model to describe noncollinear degenerate phase modulation in samples with inhomogeneities of nonlinear refractive index over all three dimensions, namely, two-layered samples and samples with local impurities. The impact of sample parameters in the considered configurations is analyzed. We show that analysis of inline digital holograms obtained by time-resolved inline digital holography can be successfully used for rapid detection and characterization of various types of nonlinear refractive index inhomogeneities.

Holographic tomography: techniques and biomedical applications [Invited].

Holographic tomography (HT) is an advanced label-free optical microscopic imaging method used for biological studies. HT uses digital holographic microscopy to record the complex amplitudes of a biological sample as digital holograms and then numerically reconstruct the sample's refractive index (RI) distribution in three dimensions. The RI values are a key parameter for label-free bio-examination, which correlate with metabolic activities and spatiotemporal distribution of biophysical parameters of cells and their internal organelles, tissues, and small-scale biological objects. This article provides insight on this rapidly growing HT field of research and its applications in biology. We present a review summary of the HT principle and highlight recent technical advancement in HT and its applications.

Influence of noise-reduction techniques in sparse-data sample rotation tomographic imaging.

Data acquisition and processing is a critical issue for high-speed applications, especially in three-dimensional live cell imaging and analysis. This paper focuses on sparse-data sample rotation tomographic reconstruction and analysis with several noise-reduction techniques. For the sample rotation experiments, a live Candida rugosa sample is used and controlled by holographic optical tweezers, and the transmitted complex wavefronts of the sample are recorded with digital holographic microscopy. Three different cases of sample rotation tomography were reconstructed for dense angle with a step rotation at every 2°, and for sparse angles with step rotation at every 5° and 10°. The three cases of tomographic reconstruction performance are analyzed with consideration for data processing using four noise-reduction techniques. The experimental results demonstrate potential capability in retaining the tomographic image quality, even at the sparse angle reconstructions, with the help of noise-reduction techniques.

Unconventional Imaging: introduction to the feature issue.

This feature issue of Applied Optics is dedicated to the international meeting of Information Photonics 2020 (IP'20), which was held September 11-12, 2020, in Taipei, Taiwan. IP'20 covered a broad range of topics, including advanced display techniques, optical computing, and optical storage. This feature issue, however, limits topics to unconventional imaging techniques, such as digital holography, artificial-intelligence associated imaging, compressive imaging, and single-pixel imaging.

Adaptive wavefront correction structured illumination holographic tomography.

In this study, a novel adaptive wavefront correction (AWC) technique is implemented on a compactly developed structured illumination holographic tomography (SI-HT) system. We propose a mechanical movement-free compact scanning architecture for SI-HT systems with AWC, implemented by designing and displaying a series of computer-generated holograms (CGH) composed of blazed grating with phase Fresnel lens on a phase-only spatial light modulator (SLM). In the proposed SI-HT, the aberrations of the optical system are sensed by digital holography and are used to design the CGH-based AWC to compensate the phase aberrations of the tomographic imaging system. The proposed method was validated using a standard Siemens star target, its potential application was demonstrated using a live candida rugosa sample, and its label-free three-dimensional refractive index profile was generated at its subcellular level. The experimental results obtained reveal the ability of the proposed method to enhance the imaging performance in both lateral and axial directions.

Digital hologram for data augmentation in learning-based pattern classification.

This study proposes a novel data augmentation method based on numerical focusing of digital holography to boost the performance of learning-based pattern classification. To conduct digital holographic data augmentation (DHDA), a complex pattern diffraction approach is used to provide the least separation of confusion in the effective diffraction regime to access the full-field wavefront information of a target sample. By using DHDA, the accessible amount of labeled data is increased to complement the data manifold and to provide various three-dimensional diffraction characteristics for improving the performance of learning-based pattern classification. Experimental results demonstrated that overall accuracy of pattern classification with DHDA (95.1%) was higher than that without DHDA (90.9%).

One-shot synthetic aperture digital holographic microscopy with non-coplanar angular-multiplexing and coherence gating.

This paper proposes one-shot synthetic aperture digital holographic microscopy using a combination of angular-multiplexing and coherence gating. The proposed angular-multiplexing technique uses multiple noncoplanar incident beams into the synthetic aperture to create tight packed passbands so as to extend spatial frequency spectrum. Coherence gating is performed to prevent the self-interference among the multiple beams. Based on the design guideline proposed herein, a phase-only spatial light modulator is employed as an adjustable blazed grating to split multiple noncoplanar beams and perform angular-multiplexing, and then using coherence gating based on low-coherence-light, superresolution imaging is achieved after one-shot acquisition.

Integrated dual-tomography for refractive index analysis of free-floating single living cell with isotropic superresolution.

Digital holographic microtomography is a promising technique for three-dimensional (3D) measurement of the refractive index (RI) profiles of biological specimens. Measurement of the RI distribution of a free-floating single living cell with an isotropic superresolution had not previously been accomplished. To the best of our knowledge, this is the first study focusing on the development of an integrated dual-tomographic (IDT) imaging system for RI measurement of an unlabelled free-floating single living cell with an isotropic superresolution by combining the spatial frequencies of full-angle specimen rotation with those of beam rotation. A novel 'UFO' (unidentified flying object) like shaped coherent transfer function is obtained. The IDT imaging system does not require any complex image-processing algorithm for 3D reconstruction. The working principle was successfully demonstrated and a 3D RI profile of a single living cell, Candida rugosa, was obtained with an isotropic superresolution. This technology is expected to set a benchmark for free-floating single live sample measurements without labeling or any special sample preparations for the experiments.

Coded aperture structured illumination digital holographic microscopy for superresolution imaging.

This paper proposes a coded aperture structured illumination (CASI) technique in digital holographic microscopy (DHM). A CASI wave is generated using two binary phase codes (0° and 120°) for spatial phase shifting. The generated CASI wave then interferes with a reference wave to form a coded Fresnel hologram at a single exposure with compressive sensing (CS) to avoid the temporal phase-shifting process of the structured illumination (SI). The CS algorithm is applied to retrieve the missing data of decoded phase-shifted SI-modulated waves, which are used to separate overlapped spatial frequencies for obtaining a larger spatial frequency coverage to provide superresolution imaging. Two phase-only spatial light modulators are applied to generate a directional SI pattern for obtaining a coded aperture with a suitable size to perform one-shot acquisition in the DHM system.

Tunable time-resolved tick-tock pulsed digital holographic microscopy for ultrafast events.

This study presents a time-resolved imaging technique for detecting ultrafast events in the sample with tunable tick-tock pulses in common-path digital holographic microscopy. The tick-tock pulses are generated from the same single femtosecond pulse source and manipulated through a spatial-multiplexing encoding/decoding scheme with two complementary binary codes for digital hologram recording and reconstruction. The spatial-multiplexing encoding/decoding scheme with compressive sensing on the Fresnel digital hologram is used to recover missing data and achieve high-fidelity wavefront reconstruction. The elapsed time of tick-tock pulses can be adjusted by changing the optical path difference between the pulse pair arms for dynamic observation at various timescales. The proposed method is applied to explore the ultrafast physical phenomenon by quantitative phase imaging with a stopwatch-like tunable timescale ranging from nanoseconds to femtoseconds.

Experimental demonstration of square Fresnel zone plate with chiral side lobes.

In this study, we introduce what we believe is a novel holographic optical element called a chiral square Fresnel zone plate (CSFZP). The chirality is imposed on a square Fresnel zone plate (SFZP) using a nonclassical technique by rotating the half-period zones relative to one another. The rotation of the half-period zones, in turn, twists the side lobes of the diffraction pattern without altering the focusing properties inherent to a SFZP. As a consequence, the beam profile is hybrid, consisting of a strong central Gaussian focal spot with gradient force similar to that generated by a lens and twisted side lobes with orbital angular momentum. The optical fields at the focal plane were calculated and found to possess a whirlpool-phase profile and a twisted intensity profile. Analysis of the field variation along the direction of propagation revealed a spiraling phase and amplitude distribution. Poynting vector plot of the fields revealed the presence of angular momentum in the regions of chiral side lobes. The phase of the CSFZPs were displayed on a phase-only reflective spatial light modulator and illuminated using a laser. The intensity patterns recorded in the experiment match the calculated ones, with a strong central focal spot and twisted side lobes. The beam pattern was implemented in an optical trapping experiment and was found to possess particle trapping capabilities.