Object Wave Research Articles

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A reflectional quantitative differential phase microscopy (RQDPM) based on polarized wavefront phase modulation and partially coherent full‐aperture illumination is introduced for imaging thick and opaque samples. RQDPM utilizes the polarization‐dependent characteristic of a phase‐type spatial light odulator to divide the object wave into two identical copies with a certain shear distance. When loading different modulation images to the spatial light modulator, phase derivative images with different shearing directions and phase shifts can be obtained. Finally, the phase distribution of the sample is obtained.For further details please visit the article by Ying Ma, Taiqiang Dai, Lan Yu, Lin Ma, Sha An, Yang Wang, Min Liu, Juanjuan Zheng, Liang Kong, Chao Zuo, and Peng Gao (e202200325).image

Reducing the computational complexity of high-resolution hologram calculations using polynomial approximation.

In this paper, we have proposed a hologram calculation method using polynomial approximations for reducing the computational complexity of point-cloud-based hologram calculations. The computational complexity of existing point-cloud-based hologram calculations is proportional to the product of the number of point light sources and hologram resolution, whereas that of the proposed method can be reduced to approximately proportional to the sum of the number of point light sources and hologram resolution by approximating the object wave with polynomials. The computation time and reconstructed image quality were compared with those of the existing methods. The proposed method was approximately 10 times faster than the conventional acceleration method, and did not produce significant errors when the object was far from the hologram.

Synchronous Phase-Shifting Interference for High Precision Phase Imaging of Objects Using Common Optics.

Quantitative phase imaging and measurement of surface topography and fluid dynamics for objects, especially for moving objects, is critical in various fields. Although effective, existing synchronous phase-shifting methods may introduce additional phase changes in the light field due to differences in optical paths or need specific optics to implement synchronous phase-shifting, such as the beamsplitter with additional anti-reflective coating and a micro-polarizer array. Therefore, we propose a synchronous phase-shifting method based on the Mach-Zehnder interferometer to tackle these issues in existing methods. The proposed method uses common optics to simultaneously acquire four phase-shifted digital holograms with equal optical paths for object and reference waves. Therefore, it can be used to reconstruct the phase distribution of static and dynamic objects with high precision and high resolution. In the experiment, the theoretical resolution of the proposed system was 1.064 µm while the actual resolution could achieve 1.381 µm, which was confirmed by measuring a phase-only resolution chart. Besides, the dynamic phase imaging of a moving standard object was completed to verify the proposed system's effectiveness. The experimental results show that our proposed method is suitable and promising in dynamic phase imaging and measurement of moving objects using phase-shifting digital holography.

Quantitative Phase Contrast Microscopy with Optimized Partially Coherent Illumination

This paper presents a partially coherent illumination quantitative phase contrast microscopic (PCI-QPCM) prototype. In the PCI-QPCM prototype, the light scattered by a rotating diffuser is coupled into a multi-mode fiber, and the output light is used as the illumination for PCI-QPCM. The illumination wave has a constrained spectrum with a diameter of tens of micrometers, which can reduce speckle noise and will not broaden the dc term of the object wave. In the Fourier plane of the object wave, grating-masked phase shifters generated by a spatial light modulator (SLM) allow for measuring the intensity of the undiffracted and diffracted components of the object wave, as well as the phase-shifted interference patterns of the two. Quantitative phase images can be reconstructed from the recorded intensity images. The proposed PCI-QPCM was demonstrated with quantitative phase imaging of a transparent waveguide and a phase-step sample.

Analog-to-digital conversion of information archived in display holograms: II. photogrammetric digitization.

We demonstrate the opportunities of photogrammetry in digitizing information about objects by acquiring a set of photographic images captured from three-dimensional scenes, which are reconstructed from volume reflection holograms. The corresponding requirements are determined for both recording the display hologram and digitizing the information reconstructed from it by photogrammetry. They include the choice of the radiation source used to reconstruct the object wave from the hologram; requirements for object positioning when recording a display hologram relative to the recording medium; and requirements for the glare minimization procedure during the construction of a photogrammetric three-dimensional model.

Influence of nanoparticle dispersion in a transparent liquid on the spatial characteristics of a four-wave radiation converter

Abstract – The spatial characteristics of a four-wave radiation converter in a transparent heterogeneous polydisperse medium are studied in this paper considering the nanoparticle flow caused by the gravity action with a normal size distribution of particle. Three ranges of average nanoparticle radii (small, intermediate and large), for which different types of spatial spectra of the object waves are characteristic, are distinguished. Shown that in the range of small average nanoparticle radii an increase in the standard deviation leads to an increase in the half-width of the spatial frequency band cut out by a four-wave radiation converter from the spatial spectrum of the object wave. In the range of intermediate average nanoparticle radii an increase in the standard deviation can lead to both an increase and a decrease in the width of the «ring» cut out by a four-wave radiation converter. At large average nanoparticle radii a change in the standard deviation doesn’t affect the spatial selectivity of the four-wave radiation converter.

Incoherent color holography lattice light-sheet for subcellular imaging of dynamic structures

The purpose of the article is to explore the need and advantages of using the incoherent color holography lattice light-sheet (ICHLLS) to provide multiwavelength quantitative monitoring of 3D cellular dynamics in live tissue to further understand complex functions of cells and cellular compartments. We have explored the use of incoherent color holography lattice light-sheet to investigate colocalization of fluorescent markers in live cells in intact tissue. Neuronal structures provide an attractive target for incoherent color holography lattice light-sheet. The cells show a complex architecture in 3D space in which signaling both between cells and within subcellular structures requires colocalization of proteins and lipids to function. During activity and over long periods it is important in understanding these signaling functions in Parkinson’s, Alzheimer’s and motoneuron diseases within live cells in intact tissue. As a proof of concept this article recalls the key aspects in lattice light-sheet imaging and provides a description of the incoherent detection system configuration to actively control dual diffractive lenses phase-shifting at multiple excitation wavelengths sequentially, and per each z-galvo scanning level, with extended field-of-view. The incoherent color holography lattice light-sheet system will allow simultaneous recording of multidimensional object waves that contain intensity in 3D space, phase, and wavelength information. We measure colocalization of fluorescence indicators introduced into live cells in intact neural tissue.

Spatial and time characteristics of a four-wave radiation converter in a parabolic waveguide with resonant nonlinearity

Spatial and temporal characteristics of a degenerate four-wave converter in a multimode waveguide with resonant nonlinearity in a scheme with counter-pumping waves are analyzed using the time response function and the point spread function. For single-mode pump waves with equal mode numbers, the dependences of the time response width on the waveguide length, the intensity of the first pump waves, and the mode number in the mode expansion of the object wave amplitude are obtained for the four-wave converter. The greatest contribution to the object wave amplitude is shown to be from the waveguide mode whose number coincides with the mode number of single-mode pump waves. For the stationary model, taking into account the spatial structure of the Gaussian pump wave leads to a monotonous decrease with a decrease in the pump beam width, followed by a constant value of the PSF module width. With single-mode pump waves with equal mode numbers, An increase in the mode number of the pump waves leads to a redistribution of energy concentrated in the side maxima of the point signal image and improvement in the quality of the wavefront reversal for a model with single-mode pump waves with equal mode numbers.

Microseismic positioning of an isolated working face under complex geological conditions and its engineering application

In view of the inability to accurately locate vibrations in isolated workings under complex geological conditions, an adaptive rotational categorization method, a downhill comparison method based on time-frequency analysis (TFA-DC method), a variable-step acceleration search method, and a dual-phase seismic source location method (TD-DL method) are proposed. A set of integrated software with features of “visualization”, “interactive” and “one-click” was developed for microseismic data processing. Results show that compared with the improved STA/LTA method, the recognition accuracy of the island working face microseismic signal by the adaptive wheel classification method is increased by 4.8%. Compared with the improved STA/LTA method, the TFA-DC method has the advantage that it can simultaneously pick up the exact p wave and the peak S wave, and the failure ratio is 0. Compared with simulated annealing algorithm and genetic algorithm, stepwise accelerated search method has better results. The standard deviation of objective function value, location error and wave velocity error are all 0. Method improves the positioning of the TD - DL detector coordinates, dual phase and coherence of known information, such as the positioning result positioning error is only the p wave and S wave ChanZhen phase positioning method of 9.5% and 14.5%, to a certain extent offset the p wave and S wave ChanZhen phase calculation of the positioning error, so as to improve the effect of source localization precision of the inversion.

Co-linear common-path shearography with a zero-approaching shear amount and separate control of the spatial carrier for single-shot phase measurement.

A co-linear common-path shearography is proposed with spatial phase shift for single-shot phase measurement. The co-linear common-path configuration brings an enhanced robustness and stability of the measuring system, because the two laterally sheared interfering object waves propagate essentially along the same path, which cancels out the disturbance and noise in surroundings. Two functional features, which break through the limitations in conventional co-linear common-path shearography, are proposed and implemented, namely the zero-approaching shear amount and the separate control of the spatial carrier. Seldom shearography configured by co-linear common-path structure possesses with these two features, because the linearly aligned optics restricts the control parameters in regards to the shear amount and the spatial carrier. In the proposed scheme, an intermediate real image plane is created in the linearly aligned light path to address the issue of zero-approaching shear amount. A 4-f imaging system is embedded with an aperture in between to implement a separate control of the spatial carrier. The zero-approaching shear amount provides the sufficiently small shear to make sure the strain or slope field of complex deformation is resolvable. Meanwhile, the separate control of the spatial carrier further guarantees a well-distributed spatial frequency spectrum when the required zero-approaching shear amount is configured.

Adaptive mixed-constraint Gerchberg-Saxton algorithm for phase-only holographic display

At present, spatial light modulators are incapable of modulating both the amplitude and phase of the wavefront simultaneously. Therefore, when a spatial light modulator is used for holographic display, it is necessary to encode the complex amplitude of the object wave into amplitude-only or phase-only computer-generated-hologram. The phase-only holographic display has attracted much attention of researchers due to its characteristics of high diffraction efficiency and no conjugate image. However, current optimization algorithms for generating phase-only hologram have the problems of iterative divergence, slow convergence speed, and poor reconstruction quality, which is difficult to satisfy the requirements for high-quality holographic display. In this work, we propose an accurate adaptive mixed constraint Gerchberg-Saxton algorithm by constraining the frequency bandwidth in the hologram plane and adaptively constraining the amplitude of the reconstructed image in the image plane based on the angular spectrum propagation theory. Firstly, we use the angular spectrum propagation model without paraxial approximation to simulate the forward and backward propagation of the light wave for ensuring the accuracy of the wavefront propagation. Secondly, dividing the image plane into signal area and noise area according to the spatial distribution of target image, and different adaptive feedback strategies are set up for the two regions based on the optimized effect of the phase-only hologram. The adaptive feedback strategy is established, which can accelerate the convergence speed of the proposed algorithm and enhance the hologram of freedom of the optimization. Finally, the frequency bandwidth constraint strategy is introduced in the hologram plane to optimize the edge pixels and compensate for the frequency information loss of the phase-only computer-generated hologram, which improves the reconstruction quality of the hologram. After 100 iterations, the average correlation coefficient of the holographic reconstructed image of the proposed algorithm is about 0.9857, and the average peak signal-to-noise ratio is about 31.02 dB. The correlation coefficient and the peak signal-to-noise ratio of the reconstructed images of the proposed algorithm are better than those of the Gerchberg-Saxton algorithm with only frequency bandwidth constraint strategy, and the proposed algorithm has clearer texture and better display effect. The results of numerical simulations and optical experiments show the feasibility and effectiveness of the proposed method. The proposed adaptive mixed constraint Gerchberg-Saxton algorithm is a promising technology for high-quality holographic display.

Expanded field of view frequency-selective incoherent holography by using a triple-beam setup.

We propose a new, to the best of our knowledge, method of incoherent optical frequency selection called three-pack frequency-selective incoherent holography. Compressed holography is reconstructed using phase shift intercepts and spatial transfer function convolution in the form of separation without loss of magnification or resolution. The frequency-selective reconstruction process removes the conjugate and DC terms along with the interception of the object wave. This work attempts three-dimensional reconstruction and selected-frequency phase extraction of axial slices in submicron steps, and the experimental results show the potential of the proposed method in areas such as compressed holography, extended field of view, and slice tomography.

Complex wave and phase retrieval from a single off-axis interferogram.

Single-frame off-axis holographic reconstruction is promising for quantitative phase imaging. However, reconstruction accuracy and contrast are degraded by noise, frequency spectrum overlap of the interferogram, severe phase distortion, etc. In this work, we propose an iterative single-frame complex wave retrieval based on an explicit model of object and reference waves. We also develop a phase restoration algorithm that does not resort to phase unwrapping. Both simulation and real experiments demonstrate higher accuracy and robustness compared to state-of-the-art methods, for both complex wave estimation and phase reconstruction. Importantly, the allowed bandwidth for the object wave is significantly improved in realistic experimental conditions (similar amplitudes for object and reference waves), which makes it attractive for large field-of-view and high-resolution imaging applications.

An interference iterative reconstruction algorithm based on a single off-axis digital hologram

Compared with in-line digital holography, off-axis digital holography can be used to image more kinds of objects without the limitation of weak phase and sparsity, but the resolution is lower. In this paper, we put forward a high-resolution iterative reconstruction algorithm for off-axis holography which requires only the recording of a single off-axis hologram. Interference and inverse interference processes are used to extract the object wave from the off-axis hologram. A frequency domain filter with increasing radius is used to improve the competitive advantage of low frequency information in the early iterations, while retaining the high frequency information. The constraints of total variation and positive absorption are implemented at the object plane to enhance the robustness of the algorithm. Numerical simulations and experiments show that the resolution of our method is higher than traditional off-axis digital holography. In addition, it is suitable for phase image when the object has a strong phase fluctuation, as well as for imaging dynamical objects.

Single-pixel imaging interferometer based on the synthesis of spatial coherence.

In this study, an interferometric method with conventional optical components without pixelated devices for the single-pixel imaging of a spatially incoherent light source is proposed. The tilting mirror performs linear phase modulation to extract each spatial frequency component from the object wave. The intensity at each modulation is detected sequentially to synthesize the spatial coherence such that the Fourier transform computation reconstructs the object image. Experimental results are provided to confirm that interferometric single-pixel imaging enables reconstruction with spatial resolution determined by the relation between the spatial frequency and tilt of the mirrors.

Computer‐Generated Holographic Nanoprinting

AbstractMetasurface‐assisted nanoprinting is usually enabled by spectrum‐modulation and/or polarization‐modulation at the subwavelength scale. The spectrum‐modulated nanoprint works under unpolarized white‐light and requires the minimalist observation conditions, but it can hardly modulate light brightness; the polarization‐modulated nanoprint can continuously control light brightness, but it requires complex and precise polarization control both at the input and output ends to decode a nanoprinting image. In this study, computer‐generated holographic nanoprinting is designed and experimentally demonstrated, enabled by Pancharatnam–Berry phase modulation of light, which has both the advantages of the two types of nanoprintings while avoiding their disadvantages. Specifically, a general platform is built to implement single‐channel/multichannel/color nanoprinting in a holography way, which presents its unique characteristics like incoherent light illumination, arbitrary brightness modulation, polarization insensitivity, and zero‐dispersion. A periodic phase is further attached to the target object wave during the holographic interference pattern generation, and the reconstructed nanoprinting image only appears in the zero‐order diffraction direction, thus making the information delivery safer. This study can empower advanced research on metasurface‐based nanoprinting, which can find its markets in ultracompact image‐display, data storage, information multiplexing, and many other related fields.

Four-wave mixing on thermal nonlinearity with feedback for signal or object waves

The coincidence of the amplitude reflection coefficients, half-widths of the spatial frequencies bands of a four-wave radiation converter on thermal nonlinearity with feedback for signal or object waves has been shown at equal pump waves intensity. The dependence of the amplitude reflection coefficient, spatial selectivity of the four-wave radiation converter on thermal nonlinearity on the pump waves intensity has been analyzed. An increase in the half-width of the spatial frequency band is observed with an increase in the pump waves intensity at the compensation for the phase shift arising as a result of the propagation of the pump waves in the medium. There is a threshold value of the pump waves intensity, above which the value of the amplitude reflection coefficient of the four-wave converter with feedback for signal or object waves, is less than in the absence of feedback.

Two-dimensional quantitative near-field phase imaging using square and hexagonal interference devices

Abstract We demonstrate the formation of the near field with non-trivial phase distribution using surface plasmon interference devices, and experimental quantitative imaging of that phase with near-field phase microscopy. The phase distribution formed with a single device can be controlled by the polarization of the external illumination and the area of the device assigned to the object wave. A comparison of the experimental data to a numerical electromagnetic model and an analytical model assigns the origin of the near-field phase to the out-of-plane electric component of surface plasmon polaritons, and also verifies the predictive power of the models. We demonstrate a formation of near-field plane waves with different propagation directions on a single device, or even simultaneously at distinct areas of a single device. Our findings open the way to the imaging and tomography of phase objects in the near field.

Spatial and temporal characteristics of a four-wave radiation converter with due regard for Earth's gravity field acting on nanoparticles dissolved in a transparent liquid

A theoretical analysis of the dynamics of the spatial spectrum of the object wave in a degenerate four-wave mixing in a transparent solution of nanoparticles in the classical scheme with counterpropagating pump waves is carried out. It is shown that when pump waves propagate orthogonally to the gravity force, a dip arises in the modulus of the spatial spectrum of the object wave, with its half-width nonmonotonically decreasing over time and increasing in the direction of gravity force with increasing radius of the nanoparticles. There is an optimal time over which the half-width of the dip in the direction of the gravity force reaches the lowest value. This time decreases monotonically with increasing nanoparticle radius, as well as with a decrease in the solution thickness.

A Study of Resolution Improvement in Noncoherent Optical Coherence Imaging

Noncoherent light, as a common light source in life, can effectively avoid problems such as scattering noise caused by optical components incoherent light imaging, and through the design of the optical path can also trigger interference and holographic imaging of objects, allowing holography to be used in more fields. Various techniques have emerged for recording holograms using incoherent light sources as technology has developed. A recording method has been proposed that exploits the correlation between the object wave information and the Fresnel band sheet to achieve incoherent hologram recording. Using a spatial light modulator (SLM) loaded with a bit-phase mask with multiplexed lens function, the incident light wavefield is phase-modulated to achieve diffraction spectroscopy and phase shifting. And holograms with different phase shifts can be obtained and combined with phase-shifting techniques to eliminate the effects of twin images caused by coaxial holography in the reproduction process. Based on the study of this incoherent holographic imaging system, the influence of the characteristics of the main components of the system and the corresponding parameters on the resolution of the recorded and reproduced holograms is investigated, and optimization methods are given from both theoretical and experimental studies. The empirical analysis of the FINCH imaging system is carried out. The observed optical path is designed, and the method of making a bit-phase mask loaded on a spatial light modulator is presented. The effect of the focal length and recording distance of the dislocation mask on the resolution of the system is investigated by both computer simulation and experimental operation.