Abstract Digital Holography (DH) enables high-accuracy quantitative phase imaging but is limited by reduced lateral resolution and coherent artifacts, such as diffraction noise, unwanted interference due to reflections and edge ringing. This work introduces Speckle Illumination Digital Holography (SIDH) for reflective surface samples, integrating DH with multiple decorrelated speckle illuminations to combine the phase sensitivity of DH with the resolution enhancement and noise suppression of incoherent imaging. An on-axis phase-shifting DH setup uses a holographic diffuser on a motorized stage to generate uncorrelated speckle fields, followed by object field reconstruction via calibration and averaging. Experiments on a USAF 1951 test target, supported by numerical simulations, demonstrate that SIDH enhances lateral phase resolution and significantly reduces edge ringing compared to plane-wave illumination. However, instrument transfer function (ITF) analysis reveals that contrast transfer decreases at higher spatial frequencies, limiting quantitative phase accuracy and preventing the full realization of theoretical resolution gains. These results highlight SIDH’s potential and limits.

Context. As the Extremely Large Telescope (ELT) approaches operational status, optimising its imaging performance is critical. A differential piston, arising from either the adaptive optics (AO) control loop, thermomechanical effects, or other sources, significantly degrades the image quality and is detrimental to the telescope’s overall performance. Aims. In a numerical simulation set-up, we propose a method for estimating the differential piston between the petals of the ELT’s M4 mirror using images from a 2 × 2 Shack-Hartmann wavefront sensor (SH-WFS), commonly used in the ELT’s tomographic AO mode. We aim to identify the limitations of this approach by evaluating its sensitivity to various observing conditions and sources of noise. Methods. Using a deep learning model based on a ResNet architecture, we trained a neural network (NN) on simulated datasets to estimate the differential piston. We assessed the robustness of the method under various conditions, including variations in Strehl ratio, polychromaticity, and detector noise. The performance was quantified using the root mean square error (RMSE) of the estimated differential piston aberration. Results. This method demonstrates the ability to extract differential piston information from 2 × 2 SH-WFS images. Temporal averaging of frames makes the differential piston signal emerge from the turbulence-induced speckle field and leads to a significant improvement in the RMSE calculation. As expected, better seeing conditions result in improved accuracy. Polychromaticity only degrades the performance by less than 5%, compared to the monochromatic case. In a realistic scenario, detector noise is not a limiting factor, as the primary limitation rather arises from the need for sufficient speckle averaging. The network was also shown to be applicable to input images other than the 2 × 2 SH-WFS data.

Abstract The demand for high performance strain sensors with both high accuracy and efficient computation is escalating in fields such as aerospace, civil engineering, and machinery manufacturing. However, integrating high measurement precision and low computational complexity in a single sensor remains a challenge. Here, we propose a multi-fiber speckle strain sensor based on structure-data fusion. The sensor is innovatively designed by optimizing the spatial topological structure of multiple fibers, with a single-turn coaxial fiber bundle as the core sensing architecture, consisting of one central transmitting fiber (TF) and six surrounding receiving fibers (RFs). When coherent light from the TF is reflected by the measured object, the RFs capture speckle patterns with strong correlation. Through coding preprocessing of these speckles and analysis via a backpropagation neural network system (including six Sub-BPNNs and one Gross-BPNN), strain measurement is achieved. As the sensor detects strain changes, the structured speckle field formed by the multi-fiber layout encodes abundant strain-feature information, reducing the complexity of subsequent signal processing. The fusion of spatial structure information and speckle data features effectively mitigates algorithmic uncertainty. Benefiting from this structure-data fusion strategy, the sensor achieves high measurement accuracy (MAE = 0.1133, RMSE = 0.1591) with low computational requirements. The proposed multi-fiber speckle sensing methodology shows significant potential for applications in complex engineering environments.

High-contrast imaging relies on advanced coronagraphs and adaptive optics (AO) to attenuate the starlight. However, residual aberrations, especially non-common path aberrations between the AO channel and the coronagraph channel, limit the instrument performance. While post-processing techniques such as spectral or angular differential imaging (ADI) can partially address those issues, they suffer from self-subtraction and inefficiencies at small angular separations or when observations are conducted far from transit. We previously demonstrated the on-sky performance of coherent differential imaging (CDI), which offers a promising alternative. It allows for isolating coherent starlight residuals through speckle modulation, which can then be subtracted from the raw images during post-processing. This work aims to validate a CDI method on real science targets using VLT/SPHERE, demonstrating its effectiveness in imaging almost face-on circumstellar disks, which are typically challenging to retrieve with ADI. We temporally modulated the speckle field in VLT/SPHERE images, applying small phase offsets on the AO deformable mirror while observing stars surrounded by circumstellar material: HR 4796A, CPD-36 6759, HD 169142, and HD 163296. We hence separated the astrophysical scene from the stellar speckle field, whose lights are mutually incoherent. Combining a dozen of data frames and reference coronagraph point spread functions through a Karhunen–Loève image projection framework, we recover the circumstellar disks without the artifacts that are usually introduced by common post-processing algorithms (e.g., self-subtraction). The CDI method therefore represents a promising strategy for calibrating the effect of static and quasi-static aberrations in future direct imaging surveys. Indeed, it is efficient, does not require frequent telescope slewing, and does not introduce image artifacts to first order.

The parametric amplification of angularly multiplexed waves is studied via modeling and experiments. The phase-matching properties of the amplification process with a single pump, including parasitic interactions of pairs of signal/idler, are investigated. An experimental demonstration with up to six signal waves is presented, with a quantification of the output properties, including stability relative to the input pump and seeds. A proof-of-concept study of beam smoothing induced by combining up to 12 speckle fields generated from six signal waves and six idler waves is shown.

We develop a prescription for constructing split-step models for computationally efficient numerical propagation of optical fields through distributed atmospheric phase screens in imaging geometries with both an aperture stop and a field stop. We use phase-space optics to show that our prescription yields efficient spatial sampling values, efficient in the sense that they closely match the minimum space-bandwidth product requirements for sampling a generic speckled field that passes through both stops. We also compute the computational complexity for propagating fields through our split-step models using fast Fourier transform methods. Compared with a typical split-step model, our efficient prescription provides more than a 6× reduction in computational complexity with excellent fidelity.

We proposed vortex beam dynamic speckle interference microscopy (VSIM), a novel, to our knowledge, imaging technique that combines dynamic speckle illumination and common-path phase-shifting interferometry for high-resolution quantitative phase imaging. By exploiting the angular properties of perfect optical vortex beams, VSIM generates a refined speckle pattern, providing clear benefits compared to traditional coherent imaging systems. Experimental validation demonstrates that VSIM improves spatial resolution by 1.39-fold and enhances the signal-to-noise ratio (SNR) from 16.4 dB to 34.3 dB. The proposed method achieved phase modulation between the scattered light from the sample and the unscattered reference light in a robust common-path configuration, which circumvents the stringent requirements of spatial correlation in speckle field interference and effectively mitigates the effects of environmental disturbances.This approach enables high-resolution, noninvasive, and label-free phase retrieval, establishing VSIM as a reliable tool for biomedical imaging, as demonstrated with red blood cells (RBCs) and A549 cells in this paper.

Speckle decorrelation noise significantly reduces the quality of phase fringe patterns in speckle interferometry. Conventional filtering methods often involve a trade-off between noise suppression and computational efficiency. To address this limitation, we propose a speckle noise suppression approach based on angular diversity in illumination. A spatial light modulator (SLM) is employed to precisely and repeatably modulate the illumination angle while simultaneously enabling temporal phase shifting. Multiple uncorrelated speckle fields are acquired and coherently averaged to reduce noise. Theoretical analysis shows that the standard deviation of the speckle noise scales inversely with the square root of the number of averages 1/N. The experimental results validate the theoretical predictions and demonstrate that the proposed method significantly suppresses speckle decorrelation noise, improving the practical performance of speckle interferometry.

The advancement of light-based structures has opened up new possibilities for controlling collective motion in various fields of study. In this paper, we show that speckle patterns (SPs), on the one hand, can be employed for smart collective manipulation of microscopic objects such as a bacterial bath. On the other hand, the analysis of SPs generated by the laser scattering from the sample can be used to detect and measure their statistical parameters. The SPs can be designed to apply different manipulation tasks on dynamic micro-objects, such as confinement, transport, and re-assembly. Simultaneously, the acquisition of sequences of SPs from such samples provides a remote, non-contact, non-invasive, and rapid methodology for phenomenological detection and measurement. We validate the integrated method by applying it on E. coli bacteria as a representative of the important class of active matter. Application of the methodology on light-sensitive and functional materials, without necessitating the identification and tracking of individual microscopic features, may introduce further opportunities.

This study introduces a vortex beam speckle imaging system for quantitative phase imaging (QPI) with high lateral resolution. By introducing vortex beams for non-diffracting speckle field regulation, the speckle size can be significantly reduced from 116.32 μm to 11.07 μm. With these advantages, the proposed imaging system has shown 1.52 folds of lateral resolution improvement compared to a traditional coherent imaging system. Furthermore, the intensity signal-to-noise ratio of the imaging system has also been improved from 13.26 dB to 30.62 dB. Transport-of-intensity equation (TIE) phase retrieval algorithms were applied to standard quantitative phase targets, and red blood cell samples were used to demonstrate the system's precise phase retrieval capability, indicating its potential applications for label-free, non-invasive biomedical imaging.

Classical ghost imaging (CGI), an extension of quantum ghost imaging (QGI), enables object reconstruction by leveraging the spatial correlation between a pair of beams. Traditionally, CGI requires a camera or point scan to capture the spatial information of the illumination source with intensity fluctuations. In this work, we propose a novel CGI scheme that utilizes an incoherent source to illuminate both the object and the modulations, without introducing any mutual interference between them. Through theoretical analysis and experimental validation, we demonstrate that the reconstruction process relies solely on the modulations and correlation signals of two single-pixel detectors. Concurrently, this scheme is also extended to ghost diffraction, verifying the correlation between two planes that are Fourier transform pairs of the speckle field. Moreover, our study reveals the intricate relationships between the speckle field, modulations, and object, and experimentally verifies the impact of speckle fields on image quality. Notably, this work provides a more comparable framework between CGI and QGI, offering a promising avenue to explore the classical–quantum relationship.

Experimental results are presented that provide insight into the physics of statistical imaging in heavily scattering random media based on measured speckle correlations as a function of the change in position of a moving object. In this way, definitive interpretation of a rather complex and earlier theory is achieved, making this work an experimental complement to that theory paper []. Motion could be natural, where the set of positions is estimated or separately obtained, or directed, where a mechanical stage can be used to adjust the object's position. In the experiment, a coherent laser illuminates two scattering diffusers, while an object is translated between them in the resulting speckled field and images are collected in a transmission configuration. Results are shown for various objects of differing size and geometry, allowing the theory to be validated and interpreted with new understanding. This work demonstrates imaging opportunities, and applications include material characterization, environmental imaging and sensing, and deep-tissue imaging. Published by the American Physical Society 2025

The mechanical properties and failure characteristics of coal have a significant impact on the efficiency of coalbed methane extraction. Cleat structures, which are widely distributed in coal reservoirs, exert a notable influence on the mechanical behavior of coal. In this study, coal-like specimens with various cleat structures were fabricated using three-dimensional printing technology, and uniaxial compression tests were conducted to investigate the effects of cleat quantity, cleat angle, and cleat combination on the mechanical behavior of coal. The experimental results reveal that as the cleat quantity increases, both the uniaxial compressive strength (UCS) and elastic modulus (E) of the specimens exhibit a decreasing trend. With increasing cleat angle, the UCS and E follow a V-shaped trend, initially decreasing and then increasing. Specimens with cleat angles of 0° and 30° primarily undergo compressive failure, while those with cleat angles of 45°, 60°, and 75° predominantly experience shear failure along the cleats. At a cleat angle of 90°, tensile splitting failure occurs. Combination cleats alter the stress distribution and load transfer paths, leading to enhanced crack propagation and coalescence during loading, which significantly reduces the load-bearing capacity of the specimens. The maximum acoustic emission (AE) energy shows a negative correlation with increasing cleat quantity, while the frequency and complexity of AE events also increase. The cleat angle has a significant nonlinear effect on the maximum AE energy, which fluctuates with increasing angles. The presence of a combination increases the compaction space required during loading, resulting in enhanced AE activity during the initial loading phase. In the early to mid-loading stages, the speckle deformation field exhibits indistinct zonal characteristics, with microcracks initiating on both sides of the preexisting cleats. As the peak stress is approached, the speckle deformation field displays clear zonal characteristics, with an increase in the number of microcracks and their coalescence into macroscopic fractures. In the post-peak stage, the displacement on both sides of the cleats further increases, leading to the complete formation and propagation of macroscopic fractures.

Our goal was to develop and experimentally validate a polarization-interference method for phase scanning of laser speckle fields generated by diffuse layers of birefringent biological tissues. This method isolates and uses new diagnostic parameters related to the “phase waves of local depolarization”. We combined polarization-interference registration with phase scanning of complex amplitude distributions in diffuse laser speckle fields to detect phase waves of local depolarization in birefringent fibrillar networks of biological tissue and measure their modulation depth. This approach led to the discovery of new criteria for differentiating various necrotic changes in diffuse histological samples of myocardial tissue from deceased individuals with “ischemic heart disease (IHD) — acute coronary insufficiency (ACI)”, even in the presence of a high level of depolarized background. To evaluate the degree of necrotic changes in the optical anisotropy of diffuse myocardial layers, a new quantitative parameter — modulation depth of local depolarization wave fluctuations — has been proposed. Using this approach, for the first time, differentiation of diffuse myocardial samples from deceased individuals with IHD and ACI was achieved with a very good 90.45% and outstanding accuracy of 95.2%.

This study focuses on the topographic structure of optical anisotropy maps (theziograms) of dehydrated blood plasma films (facies) to identify and utilize markers for diagnosing self-similarity (multifractality) in the birefringence parameters of supramolecular protein networks. The research is based on the Jones-matrix analytical framework, which describes the formation of polarization-structural speckle fields in polycrystalline blood plasma facies. In the proposed model, algorithms were developed to relate the real and imaginary parts of the complex elements of the Jones matrix to the theziograms of linear and circular birefringence. To experimentally implement these algorithms, a novel optical technology was introduced for polarization-interference registration and phase scanning of the laser speckle field of blood plasma facies. The laser-based Jones-matrix layer-by-layer theziography relies on polarization filtration and the digital recording of interference patterns from microscopic images of blood plasma facies. This process includes digital 2D Fourier reconstruction and phase-by-phase scanning of the object field of complex amplitudes, enabling the acquisition of phase sections of laser polarization-structural speckle field components scattered with varying multiplicities. Jones-matrix images of supramolecular networks, along with their corresponding theziograms of linear and circular birefringence, were obtained for each phase plane. The experimental data derived from laser layer-by-layer Jones-matrix theziography were quantitatively analyzed using two complementary approaches: statistical analysis (central moments of the 1st to 4th orders) and multifractal analysis (spectra of fractal dimension distributions). As a result, the most sensitive markers—namely asymmetry and kurtosis—were identified, highlighting changes in the statistical and scale self-similar structures of the theziograms of linear and circular birefringence in blood plasma facies. The practical aspect of this work is to evaluate the diagnostic potential of the Jones-matrix theziography method for identifying and differentiating changes in the birefringence of supramolecular networks in blood plasma facies caused by the long-term effects of COVID-19. For this purpose, a control group (healthy donors) and three experimental groups of patients, confirmed to have had COVID-19 one-to-three years prior, were formed. Within the framework of evidence-based medicine, the operational characteristics of the method—sensitivity, specificity, and accuracy—were assessed. The method demonstrated excellent accuracy in the differential diagnosis of the long-term effects of COVID-19. This was achieved by statistically analyzing the spectra of fractal dimensions of Jones-matrix theziograms reconstructed in the phase plane of single scattering within the volume of blood plasma facies.

Doppler frequency shifts associated with the motions in cells range from mHz to Hz, requiring ultra-stable interferometry to capture frequency offsets at several parts in 1018. Common-path interferometers minimize the influence of mechanical disturbances when the signal and reference share common optical elements. In this paper, multi-mode speckle self-referencing via a Fresnel biprism demonstrates frequency stability down to 1 mHz. A low-coherence NIR source creates an OCT-like pseudo-coherence-gate in Fourier-domain holography without phase stepping, and the Fourier reconstruction of the self-referencing speckle fields produces an image-domain autocorrelation of the target. Fluctuation spectroscopy of dynamic speckle is performed on a semi-solid lipid emulsion that captures Brownian thermal signatures and on feline tissue culture that measures active intracellular transport. The extension of biodynamic imaging to lower frequencies opens the opportunity for studies of cell crawling in macroscopic living tissues.

Self-cleaning of nondiffracting speckle fields in second-harmonic generation

Dynamic speckle illumination-based quantitative phase microscopy (QPM) offers the capability to eliminate coherent noise and achieve depth selection; however, the low coherence of the illumination restricts the flexibility in objective lens selection. An asymmetric reflective quantitative phase microscopy method is proposed in this Letter. The speckle field correlation is maintained through identical exit pupil diameters in the objectives of both interference arms. Moreover, a light source system with a delay line compensates for the optical path difference introduced by the asymmetric objectives, thereby achieving a high-contrast interferogram. Experimental measurements on a resolution target and a transparent sample demonstrate the dynamic phase imaging and depth-selection capabilities of the system across different fields of view.

A rough-surfaced retardation plate is a particular polarization-dependent phase modulation device, whose performance is affected by its surface roughness structures. In previous research [J. Opt. Soc. Am. A32, 2346 (2015)JOAOD60740-323210.1364/JOSAA.32.002346], its decorrelation and depolarization effects have been investigated under an assumption of a rough surface model with large covariance of thickness fluctuations, giving a fully developed speckle field by transmission/reflection. This paper continues the analysis of the rough-surfaced retardation plate and then focuses on a smooth roughness model. When the thickness fluctuation is relatively small, partially developed speckle will be generated. The statistics of partially developed polarization speckle with non-uniform spatial distribution of polarization state will be discussed in the form of the matrix elements of the coherence-polarization matrix. The propagation of the partially developed speckle field will be traced within the framework of the complex-valued ABCD matrix theory under paraxial approximation to reveal the evolution of its degree change of coherence and polarization on propagation. This means that Gaussian apertures are included in the optical train of elements. The differences in statistical features from fully developed polarization speckle are emphasized.

Abstract Orbital angular momentum (OAM) beam’s spatial information captured using a camera, employs millions of single-pixel detectors arranged in a two-dimensional matrix. Poses challenges in OAM detection due to significant storage requirements, reduced speed due to low frame rate, and increased post-processing time. To address this bottleneck, a novel OAM detection technique utilizing only a diffuser and a single-pixel fast photodiode (FPD) is reported. The sixteen OAM beams, l = [ − 8 + 8 ] interact with the rotating diffuser resulting in a temporally varying speckle field. The 1D temporal speckle information (TSI) has been segregated from the temporally varying 2D speckle pattern images for each beam. The segregated 1D TSI has been classified by employing a machine learning model and achieved a classification accuracy of 97.1% and 97.3% on simulated and experimental data respectively. To further validate the proposed single-pixel OAM detection method, the 1D TSI is captured directly using a FPD. The experimentally captured 1D TSI captured via photodiode has been classified by a lightweight custom-designed 1D convolutional neural network and achieved an increased classification accuracy of 96%. This approach redefines OAM detection, operating in the temporal domain with a single-pixel FPD, thereby significantly reducing storage and computational costs while promising high-speed OAM detection.