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- 实验方案
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Comparative appraisal of global and local thresholding methods for binarisation of off-axis digital holograms
摘要： Binary digital and computer-generated holograms are used in a number of digital micromirror device (DMD) applications, including holographic displays, media characterisation, optical encryption, and others. Binarisation is one of the most simple and e?cient methods of hologram compression. In this paper, 12 local and 18 global thresholding techniques of di?erent groups were analysed and compared based on attribute similarity, clustering, entropy, histogram shape, and local adaptive factors. Optically recorded o?-axis digital holograms of di?erent objects were binarised using these methods. The amplitude quality of the obtained reconstructed images was compared using PSNR and SSIM values. The clustering-based methods achieved the highest quality. The results of binarisation by global and local methods were comparable on average.
关键词： Image binarisation,Hologram compression,Thresholding,Digital holography,Digital image processing,Digital micromirror device
更新于2025-09-23 15:21:21
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Fast reconstruction of two-wavelength off-axis multiplexed holograms using division-multiplexing and critical sampling
摘要： Benefiting from two-wavelength information multiplexed into one hologram, two-wavelength off-axis holography can perform simultaneous quantitative phase imaging in an extended thickness range. However, its present phase processing still adopts the traditional Fourier-based method at the expense of the reconstruction speed. Hence, we propose a fast approach by combining critical sampling with division multiplexing. In our approach, the critical sampling is used to remove the redundant data, and the division multiplexing is developed to eliminate the redundant calculation processes. Experimental results illustrate that our approach can yield faster reconstruction with frame rates up to 46 fps even for one megapixel multiplexed holograms at two wavelengths on a single-core personal computer.
关键词： Critical sampling,Multiplex holography,Dual-wavelength digital holography,Fast phase retrieval
更新于2025-09-23 15:21:01
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A right-handed circularly polarized wave generated by a waveguide-fed holographic metasurface
摘要： We propose a novel method superposed two linearly polarized components to generate a right-handed circularly polarized (RCP) wave by using a holographic waveguide-fed metasurface. Combining with the holography principle and the polarizable particles based method, the expected RCP wave can be steered flexibly only by changing the slot state of each unit cell. A prototype generating a RCP wave at boresight direction is simulated, fabricated and measured, respectively. Both simulation and experiment results verify the good capability of the proposed metasurface. Applying this method, the resultant metasurface does not need a complex feeding network and can be easily extended to a reconfigurable CP metasurface. Therefore, the proposal has a huge potential in reconfigurable multifunctional CP devices.
关键词： waveguide-fed,metasurface,circularly polarized wave,holography
更新于2025-09-23 15:21:01
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Real-time pollen monitoring using digital holography
摘要： We present the ?rst validation of the Swisens Poleno, currently the only operational automatic pollen monitoring system based on digital holography. The device provides in-?ight images of all coarse aerosols, and here we develop a two-step classi?cation algorithm that uses these images to identify a range of pollen taxa. Deterministic criteria based on the shape of the particle are applied to initially distinguish between intact pollen grains and other coarse particulate matter. This ?rst level of discrimination identi?es pollen with an accuracy of 96 %. Thereafter, individual pollen taxa are recognized using supervised learning techniques. The algorithm is trained using data obtained by inserting known pollen types into the device, and out of eight pollen taxa six can be identi?ed with an accuracy of above 90 %. In addition to the ability to correctly identify aerosols, an automatic pollen monitoring system needs to be able to correctly determine particle concentrations. To further verify the device, controlled chamber experiments using polystyrene latex beads were performed. This provided reference aerosols with traceable particle size and number concentrations in order to ensure particle size and sampling volume were correctly characterized.
关键词： Swisens Poleno,pollen monitoring,particle classification,digital holography,automatic pollen monitoring system
更新于2025-09-23 15:21:01
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Nonlinear Langevin dynamics via holography
摘要： In this work, we consider non-linear corrections to the Langevin effective theory of a heavy quark moving through a strongly coupled CFT plasma. In AdS/CFT, this system can be identified with that of a string stretched between the boundary and the horizon of an asymptotically AdS black brane solution. We compute the Feynman-Vernon influence phase for the heavy quark by evaluating the Nambu-Goto action on a doubled string configuration. This configuration is the linearised solution of the string motion in the doubled black brane geometry which has been proposed as the holographic dual of a thermal Schwinger-Keldysh contour of the CFT. Our expression for the influence phase passes non-trivial consistency conditions arising from the underlying unitarity and thermality of the bath. The local effective theory obeys the recently proposed non-linear fluctuation dissipation theorem relating the non-Gaussianity of thermal noise to the thermal jitter in the damping constant. This furnishes a non-trivial check for the validity of these relations derived in the weak coupling regime.
关键词： AdS-CFT Correspondence,Holography and quark-gluon plasmas,Quantum Dissipative Systems
更新于2025-09-23 15:21:01
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The Ball-Based Origami Theorem and a Glimpse of Holography for Traversing Flows
摘要： This paper describes a mechanism by which a traversally generic ?ow v on a smooth connected (n + 1)-dimensional manifold X with boundary produces a compact n-dimensional C W -complex T (v), which is homotopy equivalent to X and such that X embeds in T (v) × R. The C W -complex T (v) captures some residual information about the smooth structure on X (such as the stable tangent bundle of X ). Moreover, T (v) is obtained from a simplicial origami map O : Dn → T (v), whose source space is a ball Dn ? ? X . The ?bers of O have the cardinality (n + 1) at most. The knowledge of the map O, together with the restriction to Dn of a Lyapunov function : X → R for v, make it possible to reconstruct the topological type of the pair (X , F(v)), were F(v) is the 1-foliation, generated by v. This fact motivates the use of the word “holography” in the title. In a qualitative formulation of the holography principle, for a massive class of ODE’s on a given compact manifold X , the solutions of the appropriately staged boundary value problems are topologically rigid.
关键词： Boundary value problems,Trajectory spaces,Manifolds with boundary,Holography,Traversing ?ows
更新于2025-09-23 15:21:01
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Image plane interference co-phasing technology for synthetic digital holography
摘要： Synthetic aperture is a high-resolution imaging technique which can extend the resolution Rayleigh limit capability of an aperture, while digital holography is a useful digital imaging tool. When synthetic aperture meets digital holography, a high-resolution image can be digitally achieved without many complex optic path adjust systems. However, because of the position errors and phase errors, the synthesis is always di?cult to realize. In this paper, we analyzed the sources and in?uences of these errors which mainly include the phase errors and the shape and position errors, then proposed a valid image plane interference based digitally co-phasing method. A combination of the SPGD (stochastic parallel gradient descent) algorithm with the KAZE-based registration algorithm was proposed to respectively correct the de-phased errors and the shape and position errors. Experiment demonstrated that a high-resolution synthesized image can be achieved with this method without any adjust of the optical path. The biggest advantage of the proposed method is that it can be applied in short and long distance situations, or one sensor is far away from another, or the sensor is large sized, or the angle among sensors is relatively big.
关键词： SPGD,Synthetic aperture,KAZE based registration,Interference imaging,Digital holography,Speckle
更新于2025-09-23 15:21:01
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Optical scanning holography for tumor extraction from brain magnetic resonance images
摘要： Tumor segmentation from magnetic resonance images (MRI) is an error-prone and time-absorbing process. Recently, optical methods have opened a new avenue to tack with the aforementioned problem. In this paper, we propose a novel architecture adapting the Optical Scanning Holography (OSH) to the detection of the abnormal tissue regions in MRI. The proposed method combines an o?-axis optical scan, performed by a heterodyne fringe pattern, and a MR image display ensured by a spatial light modulator. The output in-phase component of the scanned current is collected digitally. Hence, a high-precision distribution of biological tissues is extracted using this in-phase component. Its maximum position is exactly the one of the tumor. Meanwhile, this position is used in an Active Contour Model (ACM) to perform a fast segmentation of the extent corresponding to the tumors. Several images of brain tumors from BRATS database, with tumors having di?erent contrast and form, are used to test the proposed system. Parameters reverted by the optical process are used to investigate the detection performance. Further, in terms of tumor segmentation, the proposed OSH-ACM process has high performance metrics compared to some of recently published method. The underlying physics of the precision superiority, presented by the OSH-ACM, is the high-precision extraction of the abnormal tissue regions by the in-phase component of the scanned current.
关键词： Active contour,Optical Scanning Holography (OSH),Segmentation,Brain tumor detection,In-phase component of the scanned current
更新于2025-09-23 15:21:01
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Birefringence measurement of biological tissue based on polarization-sensitive digital holographic microscopy
摘要： We present a polarization-sensitive digital holography to measure the birefringence of biological tissues with complex structures. The birefringence measurement system is established by incorporating the modified Mach–Zehnder interferometer and lab-developed software. Normal and cancerous bladder tissue samples are measured by using the proposed experimental system. The polarization-dependent phase-shifted holograms are recorded by rotating the polarizer. Moreover, the hybrid reconstruction and least-square unwrapping algorithms are used to extract phase information of biological tissues at different polarization states. The birefringence of tissue is obtained from the above-phase distributions. The results show that polarization sensitivity exists in the normal bladder tissue and cancerous bladder tissue, and the median birefringence value of the cancerous tissue is significantly higher than that of the normal tissue. These results will provide reference for pathological research and clinic diagnoses.
关键词： Mach–Zehnder interferometer,birefringence,polarization-sensitive digital holography,biological tissue,phase distribution
更新于2025-09-23 15:21:01
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Digital holographic sizer for coal powder size distribution measurement: preliminary simulation and experiment
摘要： On-line and continuous measurements of coal powder size distribution in coal-fired plants remain challenging. A coal powder size measurement system based on digital holography (DH) is developed. The effects of several factors, i.e. pixel size, recording distance, particle size, and concentration, on particle size measurement by the DH method are quantified by simulation, yielding the suitable pixel size, recording distance and particle concentration. The measurement system is implemented based on the simulation results and applied to measure particle size distribution of pulverized coal samples. Results show that the particles are clearly reconstructed from the hologram, and the measured size distributions agree well with those of the samples measured by laser particle size analyzer. This work shows that the digital holographic sizer has great potential in coal powder size distribution measurement in power plant pipes.
关键词： digital holography,particle size distribution,coal powder,on-line measurement
更新于2025-09-23 15:21:01