Quantitative phase imaging based on holography: trends and new perspectives.

In 1948, Dennis Gabor proposed the concept of holography, providing a pioneering solution to a quantitative description of the optical wavefront. After 75 years of development, holographic imaging has become a powerful tool for optical wavefront measurement and quantitative phase imaging. The emergence of this technology has given fresh energy to physics, biology, and materials science. Digital holography (DH) possesses the quantitative advantages of wide-field, non-contact, precise, and dynamic measurement capability for complex-waves. DH has unique capabilities for the propagation of optical fields by measuring light scattering with phase information. It offers quantitative visualization of the refractive index and thickness distribution of weak absorption samples, which plays a vital role in the pathophysiology of various diseases and the characterization of various materials. It provides a possibility to bridge the gap between the imaging and scattering disciplines. The propagation of wavefront is described by the complex amplitude. The complex-value in the complex-domain is reconstructed from the intensity-value measurement by camera in the real-domain. Here, we regard the process of holographic recording and reconstruction as a transformation between complex-domain and real-domain, and discuss the mathematics and physical principles of reconstruction. We review the DH in underlying principles, technical approaches, and the breadth of applications. We conclude with emerging challenges and opportunities based on combining holographic imaging with other methodologies that expand the scope and utility of holographic imaging even further. The multidisciplinary nature brings technology and application experts together in label-free cell biology, analytical chemistry, clinical sciences, wavefront sensing, and semiconductor production.

Deep learning sheds new light on non-orthogonal optical multiplexing.

A deep neural network for non-orthogonal input channel encoding is proposed to recover speckle images through a multimode fiber. This novel approach could shed new light on the non-orthogonal optical multiplexing over a scattering medium.

Optical information hiding for different surface images.

Optical hiding often requires the selection of specific artificial optical components as carriers, which results in poor versatility of the carriers and high costs for the hiding system. To conceal secret information on different surfaces such as metal, wood, and paper, we propose an optical information hiding method. In this method, we use images of surfaces, whose grayscale histograms have the characteristic of symmetric distribution. Based on this characteristic, we first scramble the surface image, and then adjust part of the gray value of the surface image to the complementary value to embed the secret information into a scrambled surface image to generate a key image. In the extraction process, a projector is used to reproduce the scrambled surface image and the key image, which are then incoherently superimposed to extract the secret information using the human visual system. The extraction process does not require complex optical knowledge and is simple and feasible. Simulation experiments and optical experiments indicate that this method is applicable in practice and possesses good security and imperceptibility. Furthermore, we prove the reliability of this method by embedding secret information in different surface images, demonstrating the potential application of more surface images in the field of optical information hiding. Finally, we discuss the applicability of surface information images and analyze the imperceptibility of key images.

Functional Anatomy of Split Compound Eyes of the Whirligig Beetles Dineutus mellyi (Coleoptera: Gyrinidae).

The functional anatomy of the split compound eyes of whirligig beetles Dineutus mellyi (Coleoptera: Gyrinidae) was examined by advanced microscopy and microcomputed tomography. We report the first 3D visualization and analysis of the split compound eyes. On average, the dorsal and ventral eyes contain 1913 ± 44.5 facets and 3099 ± 86.2 facets, respectively. The larger area of ventral eyes ensures a higher field of vision underwater. The ommatidium of the split compound eyes is made up of laminated cornea lenses that offer protection against mechanical injuries, bullet-shaped crystalline cones that guide light to the photoreceptive regions, and screening pigments that ensure directional light passage. The photoreceptive elements, made up of eight retinular cells, exhibit a tri-tiered rhabdom structure, including the upper distal rhabdom, a clear zone that ensures maximum light passage, and an enlarged lower distal rhabdom that ensures optimal photon capture.

A self-locking mechanism of the frog-legged beetle Sagra femorata.

Insect legs play a crucial role in various modes of locomotion, including walking, jumping, swimming, and other forms of movement. The flexibility of their leg joints is critical in enabling various modes of locomotion. The frog-legged leaf beetle Sagra femorata possesses remarkably enlarged hind legs, which are considered to be a critical adaptation that enables the species to withstand external pressures. When confronted with external threats, S. femorata initiates a stress response by rapidly rotating its hind legs backward and upward to a specific angle, thereby potentially intimidating potential assailants. Based on video analysis, we identified 4 distinct phases of the hind leg rotation process in S. femorata, which were determined by the range of rotation angles (0°-168.77°). Utilizing micro-computed tomography (micro-CT) technology, we performed a 3-dimensional (3D) reconstruction and conducted relative positioning and volumetric analysis of the metacoxa and metatrochanter of S. femorata. Our analysis revealed that the metacoxa-trochanter joint is a "screw-nut" structure connected by 4 muscles, which regulate the rotation of the legs. Further testing using a 3D-printed model of the metacoxa-trochanter joint demonstrated its possession of a self-locking mechanism capable of securing the legs in specific positions to prevent excessive rotation and dislocation. It can be envisioned that this self-locking mechanism holds potential for application in bio-inspired robotics.

The Morphological Transformation of the Thorax during the Eclosion of Drosophila melanogaster (Diptera: Drosophilidae).

The model organism Drosophila melanogaster, as a species of Holometabola, undergoes a series of transformations during metamorphosis. To deeply understand its development, it is crucial to study its anatomy during the key developmental stages. We describe the anatomical systems of the thorax, including the endoskeleton, musculature, nervous ganglion, and digestive system, from the late pupal stage to the adult stage, based on micro-CT and 3D visualizations. The development of the endoskeleton causes original and insertional changes in muscles. Several muscles change their shape during development in a non-uniform manner with respect to both absolute and relative size; some become longer and broader, while others shorten and become narrower. Muscular shape may vary during development. The number of muscular bundles also increases or decreases. Growing muscles are probably anchored by the tissues in the stroma. Some muscles and tendons are absent in the adult stage, possibly due to the hardened sclerites. Nearly all flight muscles are present by the third day of the pupal stage, which may be due to the presence of more myofibers with enough mitochondria to support flight power. There are sexual differences in the same developmental period. In contrast to the endodermal digestive system, the functions of most thoracic muscles change in the development from the larva to the adult in order to support more complex locomotion under the control of a more structured ventral nerve cord based on the serial homology proposed herein.

Two new species of the Longitarsusviolentus group from China (Coleoptera, Chrysomelidae, Galerucinae, Alticini).

Two new species of Longitarsus Latreille, 1829 from China are described: L.pekingensis Liang, Konstantinov & Ge, sp. nov. (Beijing) and L.xinjiangensis Liang, Konstantinov & Ge, sp. nov. (Xinjiang). Images of dorsal and lateral habitus, pronotum, head, and male and female genitalia are provided. The records of Longitarsusviolentus Weise, 1893 and Longitarsusweisei Guillebeau, 1895 in China are discussed. Holotypes of L.marguzoricus Konstantinov in Konstantinov & Lopatin, 2000 and L.violentoides Konstantinov in Konstantinov & Lopatin, 2000 are illustrated with images of pronotum and median lobe of aedeagus. A key to species of L.violentus species group is provided.

DGE-CNN: 2D-to-3D holographic display based on a depth gradient extracting module and ZCNN network.

Holography is a crucial technique for the ultimate three-dimensional (3D) display, because it renders all optical cues from the human visual system. However, the shortage of 3D contents strictly restricts the extensive application of holographic 3D displays. In this paper, a 2D-to-3D-display system by deep learning-based monocular depth estimation is proposed. By feeding a single RGB image of a 3D scene into our designed DGE-CNN network, a corresponding display-oriented 3D depth map can be accurately generated for layer-based computer-generated holography. With simple parameter adjustment, our system can adapt the distance range of holographic display according to specific requirements. The high-quality and flexible holographic 3D display can be achieved based on a single RGB image without 3D rendering devices, permitting potential human-display interactive applications such as remote education, navigation, and medical treatment.

Adaptive constraints by morphological operations for single-shot digital holography.

Digital holography provides access to quantitative measurement of the entire complex field, which is indispensable for the investigation of wave-matter interactions. The emerging iterative phase retrieval approach enables to solve the inverse imaging problem only from the given intensity measurements and physical constraints. However, enforcing imprecise constraints limits the reconstruction accuracy and convergence speed. Here, we propose an advanced iterative phase retrieval framework for single-shot in-line digital holography that incorporates adaptive constraints, which achieves optimized convergence behavior, high-fidelity and twin-image-free reconstruction. In conjunction with morphological operations which can extract the object structure while eliminating the irrelevant part such as artifacts and noise, adaptive constraints allow the support region to be accurately estimated and automatically updated at each iteration. Numerical reconstruction of complex-valued objects and the capability of noise immunity are investigated. The improved reconstruction performance of this approach is experimentally validated. Such flexible and versatile framework has promising applications in biomedicine, X-ray coherent diffractive imaging and wavefront sensing.

Hough transform-based multi-object autofocusing compressive holography.

Reconstruction of multiple objects from one hologram can be affected by the focus metric judgment of autofocusing. Various segmentation algorithms are applied to obtain a single object in the hologram. Each object is unambiguously reconstructed to acquire its focal position, which produces complicated calculations. Herein, Hough transform (HT)-based multi-object autofocusing compressive holography is presented. The sharpness of each reconstructed image is computed by using a focus metric such as entropy or variance. According to the characteristics of the object, the standard HT is further used for calibration to remove redundant extreme points. The compressive holographic imaging framework with a filter layer can eliminate the inherent noise in in-line reconstruction including cross talk noise of different depth layers, two-order noise, and twin image noise. The proposed method can effectively obtain 3D information on multiple objects and achieve noise elimination by only reconstructing from one hologram.

Phase aberration separation for holographic microscopy by alternating direction sparse optimization.

The morphology and dynamics of label-free tissues can be exploited by sample-induced changes in the optical field from quantitative phase imaging. Its sensitivity to subtle changes in the optical field makes the reconstructed phase susceptible to phase aberrations. We import variable sparse splitting framework on quantitative phase aberration extraction based on alternating direction aberration free method. The optimization and regularization in the reconstructed phase are decomposed into object terms and aberration terms. By formulating the aberration extraction as a convex quadratic problem, the background phase aberration can be fast and directly decomposed with the specific complete basis functions such as Zernike or standard polynomials. Faithful phase reconstruction can be obtained by eliminating global background phase aberration. The aberration-free two-dimensional and three-dimensional imaging experiments are demonstrated, showing the relaxation of the strict alignment requirements for the holographic microscopes.

The fecal shield is a double-edged sword for larvae of a leaf beetle.

Larvae of some leaf beetles carry masses of feces covering parts or all of the body, which is called a "fecal shield". In general, the shield is thought to be a defense structure against natural enemies. However, some studies have suggested that defense effectiveness varies depending on the natural enemy. In this study, we used a fecal retention leaf beetle Ophrida xanthospilota (Coleoptera: Chrysomelidae), and 2 local generalist predators (an ant, Camponotus japonicus (Hymenoptera: Formicidae) and a stinkbug, Arma custos [Hemiptera: Pentatomidae]) as a system to test the hypothesis that the fecal shield of O. xanthospilota plays different roles in predation behavior of different predators and can provide multiple chemical communication signals in predator-prey interactions. Prey bioassays showed that the fecal shield of O. xanthospilota larvae repelled the ant C. japonicus while attracting the stinkbug A. custos. The results also strongly demonstrated that hexane extracts of the fecal shield significantly repelled C. japonicus, while dichloromethane (DCM) extracts did not inhibit ant predation. Interestingly, DCM extracts attracted A. custos, but hexane extracts did not. Therefore, we suggest that the fecal shield is a double-edged sword for the larvae of O. xanthospilota. Our results also indicated that the risk-benefit tradeoff of an insect should be estimated at a community level involving multiple enemies (predators and parasites) and herbivores, rather than in a single prey-predator pair.

Physics-enhanced neural network for phase retrieval from two diffraction patterns.

In this work, we propose a physics-enhanced two-to-one Y-neural network (two inputs and one output) for phase retrieval of complex wavefronts from two diffraction patterns. The learnable parameters of the Y-net are optimized by minimizing a hybrid loss function, which evaluates the root-mean-square error and normalized Pearson correlated coefficient on the two diffraction planes. An angular spectrum method network is designed for self-supervised training on the Y-net. Amplitudes and phases of wavefronts diffracted by a USAF-1951 resolution target, a phase grating of 200 lp/mm, and a skeletal muscle cell were retrieved using a Y-net with 100 learning iterations. Fast reconstructions could be realized without constraints or a priori knowledge of the samples.

Climate shapes the spatiotemporal variation in color morph diversity and composition across the distribution range of Chrysomela lapponica leaf beetle.

Color polymorphism offers rich opportunities for studying the eco-evolutionary mechanisms that drive the adaptations of local populations to heterogeneous and changing environments. We explored the color morph diversity and composition in a Chrysomela lapponica leaf beetle across its entire distribution range to test the hypothesis that environmental and climatic variables shape spatiotemporal variation in the phenotypic structure of a polymorphic species. We obtained information on 13 617 specimens of this beetle from museums, private collections, and websites. These specimens (collected from 1830-2020) originated from 959 localities spanning 33° latitude, 178° longitude, and 4200 m altitude. We classified the beetles into five color morphs and searched for environmental factors that could explain the variation in the level of polymorphism (quantified by the Shannon diversity index) and in the relative frequencies of individual color morphs. The highest level of polymorphism was found at high latitudes and altitudes. The color morphs differed in their climatic requirements; composition of colour morphs was independent of the geographic distance that separated populations but changed with collection year, longitude, mean July temperature and between-year temperature fluctuations. The proportion of melanic beetles, in line with the thermal melanism hypothesis, increased with increasing latitude and altitude and decreased with increasing climate seasonality. Melanic morph frequencies also declined during the past century, but only at high latitudes and altitudes where recent climate warming was especially strong. The observed patterns suggest that color polymorphism is especially advantageous for populations inhabiting unpredictable environments, presumably due to the different climatic requirements of coexisting color morphs.

A new genus of Languriinae from Mexico (Coleoptera, Erotylidae), with comments on the potential mimic phenomenon of some languriines.

A new genus of Languriinae, Tomolanguria Huang, gen. nov. is erected for a single species, Languria aculeata Gorham, 1887 from Mexico. It is similar to the Neotropical genus Languria Latreille, 1802. The differential diagnosis of this new genus is based on the structural features of the elytral apices and slight impressions present on each elytron. Languria aculeata is designated as the type species of the new genus. This species is redescribed and illustrated (all the three specimens examined are shown in the dorsal, ventral, and lateral views). Finally, a mimic relationship between this new genus and genus Paederus Fabricius, 1775 (Staphylinidae) is discussed.

Three-dimensional localized Airy-Gaussian wave packets in a gradient-index medium.

By solving the Schrödinger equation in spatial and temporal coordinates, the exact solution of the chirped Airy-Gaussian (CAiG) wave packets in a gradient-index medium is obtained. Based on that, we conduct a theoretical analysis about the properties of CAiG wave packets and discover that the chirp factor, the distribution factor, the initial velocity, as well as the propagation distance have an effect on the wave packets in both the propagation process and the spatiotemporal profiles. Among these, the Gaussian distribution factor, which is first added to the initial pulses, also alters the peculiarities of the Airy-Gaussian beams in the temporal domain and spatial domain. In addition, the investigation about the radiation force illuminates certain evolution properties of the CAiG wave packets well.

A taxonomic review of the genus Callilanguria Crotch, 1876 (Coleoptera: Erotylidae: Languriinae).

A worldwide review of the genus Callilanguria is presented. Three new species are described: C. weiweii Huang Yang, sp. nov. from Sabah, Malaysia; C. helleri Huang Yang, sp. nov. from Panay, the Philippines; and C. nigripes Huang Yang, sp. nov. from Samar Island, the Philippines. Callilanguria scrupulosa Heller, 1918 is transferred to the genus Doubledaya. The other species are C. eximia Fowler, 1885; C. gorhami Villiers, 1945; C. asymmetrica Heller, 1900; C. ruficeps Achard, 1923; C. milloti Villiers, 1945; C. stenosoma (Harold, 1879); C. flaviventris Fowler, 1886; C. wallacii Crotch, 1876; and C. luzonica Crotch, 1876. In total, twelve species are recognized in the genus Callilanguria, and a key to the described species of the genus is provided.

Three-dimensional localized chirped Airy-circular wave packets in free space.

By solving the (3+1)-dimensional free-space Schrödinger equation in circular cylindrical coordinates, we have systematically analyzed the propagation of chirped Airy-circular (CAiCi) wave packets. The complex amplitude of the CAiCi wave packets is constructed by the Airy function, the Gaussian function, and the confluent hypergeometric function. We find that the CAiCi wave packets are some coaxial ring pulses stacked along the temporal domain in the initial position, which are modulated by the chirped factor, the initial velocity, the distribution factor, and the propagation distance. Meanwhile, the wave packets will appear to undergo intensity attenuation, diffusion, convergence, and so on. We can also modulate the shape of the wave packets and change their optical properties by altering the mode numbers. Furthermore, we analyze the evolution properties of the wave packets in detail from the aspects of the gradient force, the scattering force, phase, the Poynting vector, and the angular momentum, and find some interesting phenomena.

Three-dimensional localized Airy-Cartesian and Airy-helical-Cartesian wave packets in free space.

We have analytically investigated three-dimensional (3D) Airy-Cartesian (AiC) and Airy-helical-Cartesian (AiHC) wave packets by solving the (3+1)-dimensional free space Schrödinger equation. The complex amplitude of the AiC and AiHC wave packets is described by the product of the Hermite polynomials, the Gaussian functions, and the Airy functions. We find that the AiC and AiHC wave packets will gradually spread along the propagation distances, but attenuate along the time domain. The distributions of the radiation force depend on the distribution factor. In addition, the chirp factor has the effect of the energy concentration of the wave packets. The different 3D spatiotemporal profiles, the photoelasticity, and vortex rings can be obtained by choosing different values of the mode number, the distribution factor, the chirp factor, the initial velocity, and the propagation distances.