Showing papers in "Journal of The Optical Society of America A-optics Image Science and Vision in 2020"

State-of-the-art active optical techniques for three-dimensional surface metrology: a review [Invited].

Abstract: This paper reviews recent developments of non-contact three-dimensional (3D) surface metrology using an active structured optical probe. We focus primarily on those active non-contact 3D surface measurement techniques that could be applicable to the manufacturing industry. We discuss principles of each technology, and its advantageous characteristics as well as limitations. Towards the end, we discuss our perspectives on the current technological challenges in designing and implementing these methods in practical applications.

TomoGAN: low-dose synchrotron x-ray tomography with generative adversarial networks: discussion.

Abstract: Synchrotron-based x-ray tomography is a noninvasive imaging technique that allows for reconstructing the internal structure of materials at high spatial resolutions from tens of micrometers to a few nanometers. In order to resolve sample features at smaller length scales, however, a higher radiation dose is required. Therefore, the limitation on the achievable resolution is set primarily by noise at these length scales. We present TomoGAN, a denoising technique based on generative adversarial networks, for improving the quality of reconstructed images for low-dose imaging conditions. We evaluate our approach in two photon-budget-limited experimental conditions: (1) sufficient number of low-dose projections (based on Nyquist sampling), and (2) insufficient or limited number of high-dose projections. In both cases, the angular sampling is assumed to be isotropic, and the photon budget throughout the experiment is fixed based on the maximum allowable radiation dose on the sample. Evaluation with both simulated and experimental datasets shows that our approach can significantly reduce noise in reconstructed images, improving the structural similarity score of simulation and experimental data from 0.18 to 0.9 and from 0.18 to 0.41, respectively. Furthermore, the quality of the reconstructed images with filtered back projection followed by our denoising approach exceeds that of reconstructions with the simultaneous iterative reconstruction technique, showing the computational superiority of our approach.

Modal analysis of structured light with spatial light modulators: a practical tutorial.

Abstract: A quantitative analysis of optical fields is essential, particularly when the light is structured in some desired manner, or when there is perhaps an undesired structure that must be corrected for. A ubiquitous procedure in the optical community is that of optical mode projections—a modal analysis of light—for the unveiling of amplitude and phase information of a light field. When correctly performed, all the salient features of the field can be deduced with high fidelity, including its orbital angular momentum, vectorial properties, wavefront, and Poynting vector. Here, we present a practical tutorial on how to perform an efficient and effective optical modal decomposition, with emphasis on holographic approaches using spatial light modulators, highlighting the care required at each step of the process.

Approaching quantum-limited imaging resolution without prior knowledge of the object location.

Abstract: Passive imaging receivers that demultiplex an incoherent optical field into a set of orthogonal spatial modes prior to detection can surpass canonical diffraction limits on spatial resolution. However, these mode-sorting receivers exhibit sensitivity to contextual nuisance parameters (e.g., the centroid of a clustered or extended object), raising questions on their viability in realistic scenarios where prior information about the scene is limited. We propose a multistage detection strategy that segments the total recording time between different physical measurements to build up the required prior information for near quantum-optimal imaging performance at sub-Rayleigh length scales. We show, via Monte Carlo simulations, that an adaptive two-stage scheme that dynamically allocates recording time between a conventional direct detection measurement and a binary mode sorter outperforms idealized direct detection alone when no prior knowledge of the object centroid is available, achieving one to two orders of magnitude improvement in mean squared error for simple estimation tasks. Our scheme can be generalized for more sophisticated tasks involving multiple parameters and/or minimal prior information.

Spatial power spectrum of natural water turbulence with any average temperature, salinity concentration and light wavelength

Abstract: The power spectrum of water optical turbulence is shown to vary with its average temperature ⟨T⟩ and average salinity concentration ⟨S⟩, as well as with light wavelength λ. This study explores such variations for ⟨T⟩∈[0∘C,30∘C], ⟨S⟩∈[0ppt,40ppt] covering most of the possible natural water conditions within the Earth's boundary layer and for visible electromagnetic spectrum, λ∈[400nm,700nm]. For illustration of the effects of these parameters on propagating light, we apply the developed power spectrum model for estimation of the scintillation index of a plane wave (the Rytov variance) and the threshold between weak and strong turbulence regimes.

On-machine surface defect detection using light scattering and deep learning

Abstract: This paper presents an on-machine surface defect detection system using light scattering and deep learning A supervised deep learning model is used to mine the information related to defects from light scattering patterns A convolutional neural network is trained on a large dataset of scattering patterns that are predicted by a rigorous forward scattering model The model is valid for any surface topography with homogeneous materials and has been verified by comparing with experimental data Once the neural network is trained, it allows for fast, accurate, and robust defect detection The system capability is validated on microstructured surfaces produced by ultraprecision diamond machining

Photoelectric switch and triple-mode frequency modulator based on dual-PIT in the multilayer patterned graphene metamaterial.

Abstract: A multilayer patterned graphene metamaterial composed of rectangular graphene, square graphene, and X-shaped graphene is proposed to achieve dual plasmon-induced transparency (PIT) at terahertz frequency. The coupled mode theory calculations are highly consistent with the finite-difference time-domain numerical results. Interestingly, a photoelectric switch has been realized, whose extinction ratio and modulation degree of amplitude can be 7.77 dB and 83.3% with the insertion loss of 7.2%. In addition, any dips can be modulated by tuning the Fermi levels of three graphene layers with minor or ignorable changes of the other two dips. The modulation degrees of frequency are 8.0%, 7.4% and 11.7%, respectively, which can be used to design a triple-mode frequency modulator. Moreover, the group index of the multilayer structure can be as high as 150. Therefore, it is reasonable to believe that a multifunctional device can be realized by the proposed structure.

Field-Only Surface Integral Equations: Scattering from a Dielectric Body

Abstract: An efficient field-only nonsingular surface integral method to solve Maxwell’s equations for the components of the electric field on the surface of a dielectric scatterer is introduced. In this method, both the vector wave equation and the divergence-free constraint are satisfied inside and outside the scatterer. The divergence-free condition is replaced by an equivalent boundary condition that relates the normal derivatives of the electric field across the surface of the scatterer. Also, the continuity and jump conditions on the electric and magnetic fields are expressed in terms of the electric field across the surface of the scatterer. Together with these boundary conditions, the scalar Helmholtz equation for the components of the electric field inside and outside the scatterer is solved by a fully desingularized surface integral method. Compared with the most popular surface integral methods based on the Stratton–Chu formulation or the Poggio–Miller–Chew–Harrington–Wu–Tsai (PMCHWT) formulation, our method is conceptually simpler and numerically straightforward because there is no need to introduce intermediate quantities such as surface currents, and the use of complicated vector basis functions can be avoided altogether. Also, our method is not affected by numerical issues such as the zero-frequency catastrophe and does not contain integrals with (strong) singularities. To illustrate the robustness and versatility of our method, we show examples in the Rayleigh, Mie, and geometrical optics scattering regimes. Given the symmetry between the electric field and the magnetic field, our theoretical framework can also be used to solve for the magnetic field.

Stochastic complex transmittance screens for synthesizing general partially coherent sources.

Abstract: We develop a method to synthesize any partially coherent source (PCS) with a genuine cross-spectral density (CSD) function using complex transmittance screens. Prior work concerning PCS synthesis with complex transmittance screens has focused on generating Schell-model (uniformly correlated) sources. Here, using the necessary and sufficient condition for a genuine CSD function, we derive an expression, in the form of a superposition integral, that produces stochastic complex screen realizations. The sample autocorrelation of the screens is equal to the complex correlation function of the desired PCS. We validate our work by generating, in simulation, three PCSs from the literature-none has ever been synthesized using stochastic screens before. Examining planar slices through the four-dimensional CSD functions, we find the simulated results to be in excellent agreement with theory, implying successful realization of all three PCSs. The technique presented herein adds to the existing literature concerning the generation of PCSs and can be physically implemented using a simple optical setup consisting of a laser, spatial light modulator, and spatial filter.

Analysis of numerical diffraction calculation methods: from the perspective of phase space optics and the sampling theorem.

Abstract: Diffraction calculations are widely used in applications that require numerical simulation of optical wave propagation. Different numerical diffraction calculation methods have their own transform and sampling properties. In this study, we provide a unified analysis where five popular fast diffraction calculation methods are analyzed from the perspective of phase space optics and the sampling theorem: single fast Fourier transform-based Fresnel transform, Fresnel transfer function approach, Fresnel impulse response approach, angular spectrum method, and Rayleigh-Sommerfeld convolution. The evolutions of an input signal's space-bandwidth product (SBP) during wave propagation are illustrated with the help of a phase space diagram (PSD) and an ABCD matrix. It is demonstrated that all of the above methods cannot make full use of the SBP of the input signal after diffraction; and some transform properties have been ignored. Each method has its own restrictions and applicable range. The reason why different methods have different applicable ranges is explained with physical models. After comprehensively studying and comparing the effect on the SBP and sampling properties of these methods, suggestions are given for choosing the proper method for different applications and overcoming the restrictions of corresponding methods. The PSD and ABCD matrix are used to illustrate the properties of these methods intuitively. Numerical results are presented to verify the analysis, and potential ways to develop new diffraction calculation methods are also discussed.

Field-only surface integral equations: scattering from a perfect electric conductor

Abstract: A field-only boundary integral formulation of electromagnetics is derived without the use of surface currents that appear in the Stratton–Chu formulation. For scattering by a perfect electrical conductor (PEC), the components of the electric field are obtained directly from surface integral equation solutions of three scalar Helmholtz equations for the field components. The divergence-free condition is enforced via a boundary condition on the normal component of the field and its normal derivative. Field values and their normal derivatives at the surface of the PEC are obtained directly from surface integral equations that do not contain divergent kernels. Consequently, high-order elements with fewer degrees of freedom can be used to represent surface features to a higher precision than the traditional planar elements. This theoretical framework is illustrated with numerical examples that provide further physical insight into the role of the surface curvature in scattering problems.

Pixel reassignment in image scanning microscopy: a re-evaluation.

Abstract: Image scanning microscopy is a technique based on confocal microscopy, in which the confocal pinhole is replaced by a detector array, and the resulting image is reconstructed, usually by the process of pixel reassignment. The detector array collects most of the fluorescent light, so the signal-to-noise ratio is much improved compared with confocal microscopy with a small pinhole, while the resolution is improved compared with conventional (wide-field) microscopy. In previous studies, it has usually been assumed that pixels should be reassigned by a constant factor, to a point midway between the illumination and detection spots. Here it is shown that the peak intensity of the effective point spread function (PSF) can be further increased by 4% by a new choice of the pixel reassignment factor. For an array of two Airy units, the peak of the effective PSF is 1.90 times that of a conventional microscope, and the transverse resolution is 1.53 times better. It is confirmed that image scanning microscopy gives optical sectioning strength identical to that of a confocal microscope with a pinhole equal to the size of the detector array. However, it is shown that image scanning microscopy exhibits axial resolution superior to a confocal microscope with a pinhole the same size as the detector array. For a two-Airy-unit array, the axial resolution is 1.34 times better than in a conventional microscope for the standard reassignment factor, and 1.28 times better for the new reassignment factor. The axial resolution of a confocal microscope with a two-Airy-unit pinhole is only 1.04 times better than conventional microscopy. We also examine the signal-to-noise ratio of a point object in a uniform background (called the detectability), and show that it is 1.6 times higher than in a confocal microscope.

Global polarizability matrix method for efficient modeling of light scattering by dense ensembles of non-spherical particles in stratified media.

Abstract: We introduce a numerical method that enables efficient modeling of light scattering by large, disordered ensembles of non-spherical particles incorporated in stratified media, including when the particles are in close vicinity to each other, to planar interfaces, and/or to localized light sources. The method consists of finding a small set of fictitious polarizable elements—or numerical dipoles—that quantitatively reproduces the field scattered by an individual particle for any excitation and at an arbitrary distance from the particle surface. The set of numerical dipoles is described by a global polarizability matrix that is determined numerically by solving an inverse problem relying on fullwave simulations. The latter are classical and may be performed with any Maxwell’s equations solver. Spatial non-locality is an important feature of the numerical dipoles set, providing additional degrees of freedom compared to classical coupled dipoles to reconstruct complex scattered fields. Once the polarizability matrix describing scattering by an individual particle is determined, the multiple scattering problem by ensembles of such particles in stratified media can be solved using a Green tensor formalism and only a few numerical dipoles, thereby with a low physical memory usage, even for dense systems in close vicinity to interfaces. The performance of the method is studied with the example of large high-aspect-ratio high-index dielectric cylinders. The method is easy to implement and may offer new possibilities for the study of complex nanostructured surfaces, which are becoming widespread in emerging photonic technologies.

Multi-view fringe projection system for surface topography measurement during metal powder bed fusion.

Abstract: Metal powder bed fusion (PBF) methods need in-process measurement methods to increase user confidence and encourage further adoption in high-value manufacturing sectors. In this paper, a novel measurement method for PBF systems is proposed that uses multi-view fringe projection to acquire high-resolution surface topography information of the powder bed. Measurements were made using a mock-up of a commercial PBF system to assess the system’s accuracy and precision in comparison to conventional single-view fringe projection techniques for the same application. Results show that the multi-view system is more accurate, but less precise, than single-view fringe projection on a point-by-point basis. The multi-view system also achieves a high degree of surface coverage by using alternate views to access areas not measured by a single camera.

Suprathreshold contrast response in normal and anomalous trichromats.

Abstract: Maximum likelihood difference scaling was used to measure suprathreshold contrast response difference scales for low-frequency Gabor patterns, modulated along luminance and L-M color directions in normal, protanomalous, and deuteranomalous observers. Based on a signal-detection model, perceptual scale values, parameterized as $ d^\prime $d', were estimated by maximum likelihood. The difference scales were well fit by a Michaelis-Menten model, permitting estimates of response and contrast gain parameters for each subject. Anomalous observers showed no significant differences in response or contrast gain from normal observers for luminance contrast. For chromatic modulation, however, anomalous observers displayed higher contrast and lower response gain compared to normal observers. These effects cannot be explained by simple pigment shift models, and they support a compensation mechanism to optimize the mapping of the input contrast range to the neural response range. A linear relation between response and contrast gain suggests a neural trade-off between them.

Introduction to electromagnetic scattering, part II: tutorial

Abstract: In this paper, some generalizations of electromagnetic scattering problems by elementary shapes are presented. In particular, the aim of the paper is to provide solutions to the scattering problem by multiple objects with simple shapes, either in concentric configuration or arbitrarily distributed in the space. The vector harmonics, representing the fields, and their properties are applied in order to solve five different problems: the electromagnetic scattering by an infinitely long circular stratified cylinder, by a multilayered sphere, by an ensemble of parallel cylinders, by an ensemble of multi-spheres, and ultimately by a sphere embedded in a circular cylinder. Numerical results in particularly important configurations are shown.

Absolute laser ranging by time-of-flight measurement of ultrashort light pulses [Invited]

Abstract: Ultrashort pulse lasers are emerging as an advanced tool of distance measurement, with their unique temporal and spectral characteristics being extended to diverse principles of absolute ranging and instrumentation Here, a systematic methodology is presented for absolute ranging by means of the time-of-flight measurement of ultrashort light pulses using dual-comb asynchronous optical sampling Based on an elaborate uncertainty analysis, influencing system parameters such as the pulse duration, repetition rate, and averaging time are optimized to achieve a sub-µm measurement accuracy The absolute ranging system developed in this study demonstrates a combined standard uncertainty of 0986 µm for a 05 ms averaging over a distance range of 30 m, with a further reduction to 0056 µm when the averaging time is increased to 05 s The outstanding performance leads to unprecedented multitarget applications: machine feed control with thermal error compensation in real time as well as the nondestructive inspection of multilens assembly in a production line

Superconical aplanatic ovoid singlet lenses.

Abstract: In this work, we return to Descartes's idea to develop a formalism to construct rigorously stigmatic singlet lenses comprising two Cartesian surfaces. Optical systems are built using a considerable number of spherical surfaces, presenting in most cases spherical aberration. Wasermann and Wolf proposed eliminating spherical aberration and minimizing third-order coma by using two adjacent aspherical surfaces. That is why, using a parametric formulation for Cartesian ovals, we propose the design of singlet lenses where the condition of rigorous stigmatism is guaranteed for each surface, and therefore, strictly speaking, in the pair of stigmatic points, the lens becomes an optical system free of spherical aberration. This formulation is unified to both refractive and reflective optical surfaces. Therefore, within the framework of the theory of rigorously stigmatic optical systems, making use of Cartesian surfaces for the construction of stigmatic ovoid singlet lenses, we achieve the same functionality of optical systems involving a set of spherical lenses. These lenses have the advantage of being formulated according to a generalized shape factor associated with the Coddington shape factor, allowing an easy classification of these stigmatic lenses. The ideal imaging is carried out by applying an exact ray-tracing method through these ovoid singlet lenses.

Fourier optics modeling of interference microscopes

Abstract: We propose a practical theoretical model of an interference microscope that includes the imaging properties of optical systems with partially coherent illumination. We show that the effects on measured topography of a spatially extended, monochromatic light source at low numerical apertures can be approximated in a simplified model that assumes spatially coherent light and a linear, locally shift-invariant transfer function that accounts for optical aberrations and the attenuation of diffracted plane wave amplitudes with increasing spatial frequencies. Simulation of instrument response using this model agrees with methods using numerical pupil-plane integration and with an experimental measurement of surface topography.

Digital Stokes polarimetry and its application to structured light: tutorial.

Abstract: Stokes polarimetry is a mature topic in optics, most commonly performed to extract the polarization structure of optical fields for a range of diverse applications. For historical reasons, most Stokes polarimetry approaches are based on static optical polarization components that must be manually adjusted, prohibiting automated, real-time analysis of fast changing fields. Here we provide a tutorial on performing Stokes polarimetry in an all-digital approach, exploiting a modern optical toolkit based on liquid-crystal-on-silicon spatial light modulators and digital micromirror devices. We explain in a tutorial fashion how to implement two digital approaches, based on these two devices, for extracting Stokes parameters in a fast, cheap, and dynamic manner. After outlining the core concepts, we demonstrate their applicability to the modern topic of structured light, and highlight some common experimental issues. In particular, we illustrate how digital Stokes polarimetry can be used to measure key optical parameters such as the state of polarization, degree of vectorness, and intra-modal phase of complex light fields.

Tunable bifunctional polarization-independent metamaterial device based on Dirac semimetal and vanadium dioxide.

Abstract: In this study, a tunable bifunctional polarization-independent metamaterial device based on Dirac semimetal films (DSFs) and vanadium dioxide (VO2) is investigated. At the VO2 insulator state, a polarization-independent electromagnetically induced reflectance effect can be achieved via destructive interference between bright and dark modes. When VO2 transitions to a metallic state, the proposed device behaves as a dual-band polarization-independent absorber with 99.9% and 94.5% absorptance at 9.06 and 10.9 THz, respectively, and is insensitive over a wide range of incidence angles. In both cases, refractive index sensing is achieved, and the response can be dynamically tuned by changing the Fermi energy of the DSF.

Relative contributions of melanopsin to brightness discrimination when hue and luminance also vary.

Abstract: A large number of studies have shown the effect of melanopsin-dependent retinal ganglion cells on humans performing brightness discrimination tasks. These studies often utilized targets that only differ in their melanopsin activation levels, and not in their luminance or hue, which are both factors that make large contributions to brightness discrimination. The purpose of the present study was to evaluate the relative contribution of melanopsin activation to brightness discrimination when luminance and hue are also varying in addition to melanopsin activation. Using an apparatus consisting of three separate high luminance projectors, we were able to manipulate melanopsin-isolating stimulation, and L-, M-, and S-cone stimulation separately, thus allowing us to vary stimuli in their melanopsin activation, luminance, and hue category independently. We constructed three sets of target stimuli with three different levels of melanopsin activation (100%, 131%, and 167% relative melanopsin excitation) and five levels of luminance. We then had subjects do a two-alternative forced choice task where they compared the previously described target stimuli set to a set of four comparison stimuli that varied in their hue category but had identical luminances. We found that in our stimuli set the overall contribution of melanopsin activity to brightness discrimination was small (an average of 6% increase in likelihood to call a high melanopsin activity stimulus brighter compared to a low melanopsin activity stimulus) when luminance and hue also varied. However, a significant interaction showed that when the comparison was between stimuli differing only in melanopsin stimulation (with luminance and hue unchanged) the contribution of melanopsin to brightness judgments was about 3 times larger (an average of 18% increase in likelihood to call a high melanopsin activity stimulus brighter compared to a low melanopsin activity stimulus). This suggests that although luminance and hue have large effects on brightness discrimination such that the melanopsin contribution can become hard to detect, when there are minimal cone-dependent signals available, melanopsin can make a large contribution to brightness discrimination.

In vitro monitoring of photoinduced necrosis in HeLa cells using digital holographic microscopy and machine learning.

Abstract: Digital holographic microscopy supplemented with the developed cell segmentation and machine learning and classification algorithms is implemented for quantitative description of the dynamics of cellular necrosis induced by photodynamic treatment in vitro. It is demonstrated that the developed algorithms operating with a set of optical, morphological, and physiological parameters of cells, obtained from their phase images, can be used for automatic distinction between live and necrotic cells. The developed classifier provides high accuracy of about 95.5% and allows for calculation of survival rates in the course of cell death.

Observer metamerism in commercial displays.

Abstract: Two uniform patches presented on two displays under identical viewing conditions can appear as the same color to one observer but as mismatched colors to another observer. This phenomenon, called observer metamerism (OM), occurs due to individual differences in color matching functions. To avoid its potentially adverse impacts in display calibration and characterization, it is desirable to have a predictive model of OM. In this work, we report the computational results of how to use existing metrics to quantify the potential OM between commercial display pairs and a proposed OM metric that is verified through a psychophysical experiment.

Machine learning-aided classification of beams carrying orbital angular momentum propagated in highly turbid water.

Abstract: A set of laser beams carrying orbital angular momentum is designed with the objective of establishing an effective underwater communication link. Messages are constructed using unique Laguerre–Gauss beams, which can be combined to represent four bits of information. We report on the experimental results where the beams are transmitted through highly turbid water, reaching approximately 12 attenuation lengths. We measured the signal-to-noise ratio in each test scenario to provide characterization of the underwater environment. A convolutional neural network was developed to decode the received images with the objective of successfully classifying messages quickly. We demonstrate near-perfect classification in all scenarios, provided the training set includes some images taken under the same underwater conditions.

Digital sorting perturbed Laguerre-Gaussian beams by radial numbers.

Abstract: We developed a new alterative technique of the digital sorting of Laguerre-Gaussian beams (LG) by radial numbers resorting to algebra of the high-order intensity moments. The term "digital mode sorting" involves sorting the main mode characteristics (in the form of a mode spectrum) by the computer cells. If necessary, the spatial mode spectrum can be reproduced, for example, by means of a spatial light modulator. In the experiment, we investigated both a single LG mode and a composition of LG modes with the same topological charge but different radial numbers subjected to perturbations via a hard-edged circular aperture. The LG beams sorting was accomplished by monitoring the amplitude spectrum of the triggered secondary LG modes then recovering the sorted modes and the perturbed beam as a whole. We have revealed degenerate states of the perturbed LG beam composition when the one kth mode in the amplitude spectrum can be related to a set of LG modes with the same radial numbers. In order to decrypt and to sort beams in such a degenerate state, it is necessary to know several keys, the number of which is equal to the number of LG modes in the initial wave composition. We were also able to analyze and to sort such degenerate mode states. For monitoring the measure of uncertainty arising in the perturbed beam, we measured informational entropy (Shannon entropy).

Passive non-line-of-sight imaging using plenoptic information

Abstract: We present a methodology for recovering the perspective imagery of a non-line-of-sight scene based on plenoptic observations of indirect photons scattered from a homogeneous surface. Our framework segregates the visual contents observed along the scattering surface into angular and spatial components. Given the reflectance characteristics of the scatterer, we show that the former can be deduced from scattering measurements employing diversity in angle at individual surface points, whereas the latter can be deduced from captured images of the scatterer based on prior knowledge of occlusions within the scene. We then combine the visual contents from both components into a plenoptic modality capable of imaging at higher resolutions than what is allowed by the angular information content and discriminating against extraneous signals in complex scenes that spatial information struggles to discern. We demonstrate the efficacy of this approach by reconstructing the imagery of test scenes from both synthetic and measured data.

Estimating and measurement of atmospheric optical turbulence according to balloon-borne radiosonde for three sites in China.

Abstract: The distribution of optical turbulence (Cn2 profiles) is the fundamental parameter closely related to the design and application of optoelectronic systems. Since systematic direct measurements of optical turbulence for many climates and seasons are not available, it is useful to estimate Cn2 effectively from the routine meteorological parameters. The Cn2 profiles are estimated by routine meteorological parameters based on the Tatarskii model, and the estimated results are compared with the corresponding radiosonde measurements from the field campaigns at Rongcheng (122.37∘E, 37.15∘N), Taizhou (121.42∘E, 28.62∘N), and Dachaidan (95.35∘E, 37.74∘N) in China. The agreement between the estimation model and the measurement is very close, except for a portion of the atmosphere where it showed considerable difference. Additionally, statistical operators are used to quantify the performance of the estimated model, and the statistical results also show that the estimated and measured Cn2 profiles are consistent well. Furthermore, the integrated parameters (such as the Fried parameter, r0) from radiosonde measurement are 7.92 cm, 5.39 cm, and 3.68 cm at Rongcheng, Taizhou, and Dachaidan, respectively. Therefore, the Cn2 profiles and their characteristics in these typical climate sites provide useful information to assess the effect of laser transmission in the atmosphere, which are usually used in the design of optoelectronic systems and astronomical site testing.

Quantifying the loss of information from binning list-mode data.

Abstract: List-mode data are increasingly being used in single photon emission computed tomography (SPECT) and positron emission tomography (PET) imaging, among other imaging modalities. However, there are still many imaging designs that effectively bin list-mode data before image reconstruction or other estimation tasks are performed. Intuitively, the binning operation should result in a loss of information. In this work, we show that this is true for Fisher information and provide a computational method for quantifying the information loss. In the end, we find that the information loss depends on three factors. The first factor is related to the smoothness of the mean data function for the list-mode data. The second factor is the actual object being imaged. Finally, the third factor is the binning scheme in relation to the other two factors.

Non-interferometric technique to realize vector beams embedded with polarization singularities

Abstract: In this paper, we present a simple and flexible non-interferometric method to generate various polarization singularity lattice fields. The proposed method is based on a double modulation technique that uses a single reflective spatial light modulator to generate different lattice structures consisting of V-point and C-point polarization singularities. The present technique is compact with respect to previous experimental realization techniques. Different structures having star and lemon fields are generated without altering the experimental setup. In addition, the same setup can be used to obtain different types of inhomogeneous fields embedded with isolated polarization singularities even of higher orders. The Stokes polarimetry method has been used to obtain the polarization distributions of generated fields, which are in good agreement with simulated results.