Showing papers on "Physical optics published in 2020"
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TL;DR: A review of the recent results on the generation and observation of polarization singularities in metaphotonics can be found in this article, where a discussion of various photonic-crystal structures, for which both near and far-field patterns manifest diverse polarization singularity characterized by the integer Poincare or more general half-integer Hopf indices (topological charges).
Abstract: Polarization singularities of vectorial electromagnetic fields locate at the positions (such as points, lines, or surfaces) where properties of polarization ellipses are not defined. They are manifested as circular and linear polarization, for which respectively the semi-major axes and normal vectors of polarization ellipses become indefinite. First observed in conical diffraction in the 1830s, the field of polarization singularities has been systematically reshaped and deepened by many pioneers of wave optics. Together with other exotic phenomena such as non-Hermiticity and topology, polarization singularities have been introduced into the vibrant field of nanophotonics, rendering unprecedented flexibilities for manipulations of light-matter interactions at the nanoscale. Here we review the recent results on the generation and observation of polarization singularities in metaphotonics. We start with the discussion of polarization singularities in the Mie theory, where both electric and magnetic multipoles are explored from perspectives of local and global polarization properties. We then proceed with the discussion of various photonic-crystal structures, for which both near- and far-field patterns manifest diverse polarization singularities characterized by the integer Poincare or more general half-integer Hopf indices (topological charges). Next, we review the most recent studies of conversions from polarization to phase singularities in scalar wave optics, demonstrating how bound states in the continuum can be exploited to generate directly optical vortices of various charges. Throughout our paper, we discuss and highlight several fundamental concepts and demonstrate their close connections and special links to metaphotonics. We believe polarization singularities can provide novel perspectives for light-matter manipulation for both fundamental studies and their practical applications.
39 citations
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20 Feb 2020TL;DR: In this article, the authors derive a general link between the degree of polarization and wave-particle duality of light and derive a measure describing the complementarity strength between photon path predictability and Stokes visibility, taking into account both intensity and polarization variations in the observation plane.
Abstract: The dual wave–particle nature of light and the degree of polarization are fundamental concepts in quantum physics and optical science, but their exact relation has not been explored within a full vector-light quantum framework that accounts for interferometric polarization modulation. Here, we consider vector-light quantum complementarity in double-pinhole photon interference and derive a general link between the degree of polarization and wave–particle duality of light. The relation leads to an interpretation for the degree of polarization as a measure describing the complementarity strength between photon path predictability and so-called Stokes visibility, the latter taking into account both intensity and polarization variations in the observation plane. It also unifies results advanced in classical studies by showing that the degree of polarization can be viewed as the ability of a light beam to exhibit intensity and polarization-state fringes. The framework we establish thus provides novel aspects and deeper insights into the role of the degree of polarization in quantum-light complementarity and photon interference.
29 citations
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TL;DR: In this article, the time delay between two signals in the presence of lensing was analyzed for binary sources with an associated electromagnetic counterpart, and it was shown that during the inspiral of a binary, peaks of the GW waveform can arrive before their EM counterpart.
Abstract: We consider gravitational wave (GW) sources with an associated electromagnetic (EM) counterpart and analyze the time delay between both signals in the presence of lensing. If GWs have wavelengths comparable to the Schwarzschild radius of astrophysical lenses, they must be treated with wave optics, whereas EM waves are typically well within the approximation of geometric optics. With concrete examples, we confirm that the GW signal never arrives before its EM counterpart, if both are emitted at the same time. However, during the inspiral of a binary, peaks of the GW waveform can arrive before their EM counterpart. We stress that this is only an apparent superluminality, since the GW waveform is both distorted and further delayed with respect to light. In any case, measuring the multimessenger time delay and correctly interpreting it has important implications for unveiling the distribution of lenses, testing the nature of gravity, and probing the cosmological expansion history.
21 citations
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TL;DR: In this paper, the evolutions of polarization and orbital angular momentum (OAM) states of light in helically twisted birefringent photonic crystal fibers (TB-PCFs) are analyzed.
Abstract: The evolutions of polarization and orbital angular momentum (OAM) states of light in helically twisted birefringent photonic crystal fibers (TB-PCFs) are analyzed. It is shown that a circular polarization (CP) component (S3 of a Stokes parameter) is periodically excited when usual linearly polarized (LP) modes of PCF are launched. The excitation originates from a geometric phase in TB-PCFs. The S3 excitation is larger for larger linear birefringence for a fixed twisting rate. If the linear birefringence is large enough, a CP filtering behavior can be seen in addition to the S3 excitation. From the analytical consideration of the sign of the geometric phase, the TB-PCF with periodical inversion of twisting is proposed to generate arbitrary polarization state on the Poincare sphere. Next, an OAM state generation in multimode TB-PCFs is shown for higher-order LP mode input. By observing a far-field interference pattern from TB-PCF mixed with LP01 mode, a vortex associated with the OAM state can be seen. Similar to the single-mode case, by using periodical twisting inversion, efficient OAM generation is possible. These results indicate that by simply launching fiber’s LP mode into TB-PCF, arbitrary polarization and OAM states can be generated, leading to a novel mechanism for the manipulation of the spatial state of light.
20 citations
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TL;DR: In this article, the backward scattering characteristics of the perfect electrical conductor (PEC) sphere and PEC cone were analyzed for axial symmetric objects, and the radar cross section for PEC sphere and cone were calculated, respectively.
Abstract: To evaluate the interaction between the orbital angular momentum (OAM) beams and the electrically large standard objects, the backward scattering characteristics of the perfect electrical conductor (PEC) sphere and PEC cone are studied. First, the incident vortex electromagnetic field carrying OAM is generated by Hertizian dipole arrays. Subsequently, the backward-scattered field is calculated by the physical optics algorithm. The phase profiles and OAM spectra are analyzed in detail, which indicates that the scattered field for axial symmetric objects still keeps the main characters of the vortex field due to the angular momentum conservation. Finally, the radar cross section for PEC sphere and cone are calculated, respectively. The backward scattering features show significant differences when OAM beams change their topological charges. Consequently, given a specific propagation direction, compared to plane waves, more information will be offered by the OAM beams for object detection and recognition.
20 citations
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TL;DR: A theory of generalized ray-wave duality is put forward, describing all previous geometric modes as well as new classes of RWD geometric modes that cannot be generated from laser cavities that are verified by the free-of-cavity creation method.
Abstract: Structured lights, particularly those with tunable and controllable geometries, are highly topical due to a myriad of their applications from imaging to communications. Ray-wave duality (RWD) is an exotic physical effect in structured light that the behavior of light can be described by both the geometric ray-like trajectory and a coherent wave-packet, thus providing versatile degrees of freedom (DoFs) to tailor more general structures. However, the generation of RWD geometric modes requires a solid-state laser cavity with strict mechanical control to fulfill the ray oscillation condition, which limits the flexiblility of applications. Here we overcome this confinement to generate on-demand RWD geometric modes by digital holographic method in free space without a cavity. We put forward a theory of generalized ray-wave duality, describing all previous geometric modes as well as new classes of RWD geometric modes that cannot be generated from laser cavities, which are verified by our free-of-cavity creation method. Our work not only breaks the conventional cavity limit on RWD but also enriches the family of geometric modes. More importantly, it offers a new way of digitally tailoring RWD geometric modes on-demand, replacing the prior mechanical control, and opening up new possibilities for applications of ray-wave structured light.
19 citations
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TL;DR: In this article, wave-optics simulations were used to look at the Monte Carlo averages associated with turbulence and time-dependent thermal blooming (TDTB), and the results showed that the log-amplitude variance and branch-point density increase significantly due to TTBI.
Abstract: Part II of this two-part paper uses wave-optics simulations to look at the Monte Carlo averages associated with turbulence and time-dependent thermal blooming (TDTB). The goal is to investigate turbulence thermal blooming interaction (TTBI). At wavelengths near 1 μm, TTBI increases the amount of constructive and destructive interference (i.e., scintillation) that results from high-power laser beam propagation through distributed-volume atmospheric aberrations. As a result, we use the spherical-wave Rytov number, the number of wind-clearing periods, and the distortion number to gauge the strength of the simulated turbulence and TDTB. These parameters simply greatly given propagation paths with constant atmospheric conditions. In addition, we use the log-amplitude variance and the branch-point density to quantify the effects of TTBI. These metrics result from a point-source beacon being backpropagated from the target plane to the source plane through the simulated turbulence and TDTB. Overall, the results show that the log-amplitude variance and branch-point density increase significantly due to TTBI. This outcome poses a major problem for beam-control systems that perform phase compensation.
19 citations
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24 Apr 2020TL;DR: Differences between the exact and approximated solutions are explored by characterizing errors made in different spatial positions and acquisition methods (confocal, non-confocal scanning) and a lateral resolution is derived based on the exact phasor field propagator, which can be used as a reference for theoretical evaluations and comparisons.
Abstract: Non-Line-of-Sight imaging has been linked to wave diffraction by the recent phasor field method. In wave optics, the Wigner Distribution Function description for an optical imaging system is a powerful analytical tool for modeling the imaging process with geometrical transformations. In this paper, we focus on illustrating the relation between captured signals and hidden objects in the Wigner Distribution domain. The Wigner Distribution Function is usually used together with approximated diffraction propagators, which is fine for most imaging problems. However, these approximated diffraction propagators are not valid for Non-Line-of-Sight imaging scenarios. We show that the exact phasor field propagator (Rayleigh-Sommerfeld Diffraction) does not have a standard geometrical transformation, as compared to approximated diffraction propagators (Fresnel, Fraunhofer diffraction) that can be represented as shearing or rotation in the Wigner Distribution Function domain. Then, we explore differences between the exact and approximated solutions by characterizing errors made in different spatial positions and acquisition methods (confocal, non-confocal scanning). We derive a lateral resolution based on the exact phasor field propagator, which can be used as a reference for theoretical evaluations and comparisons. For targets that lie laterally outside a relay wall, the loss of resolution is geometrically illustrated in the context of the Wigner Distribution Function.
17 citations
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TL;DR: A new theoretical framework using wave optics to explain the working mechanism of the grating based X-ray differential phase contrast imaging (XPCI) interferometer systems consist of more than one phase grating, which indicated that it is better to keep the periods of the two phase gratings different to generate large period diffraction fringes.
Abstract: In this work, we developed a new theoretical framework using wave optics to explain the working mechanism of the grating based X-ray differential phase contrast imaging (XPCI) interferometer systems consist of more than one phase grating. Under the optical reversibility principle, the wave optics interpretation was simplified into the geometrical optics interpretation, in which the phase grating was treated as a thin lens. Moreover, it was derived that the period of an arrayed source, e.g., the period of a source grating, is always equal to the period of the diffraction fringe formed on the source plane. When a source grating is utilized, the theory indicated that it is better to keep the periods of the two phase gratings different to generate large period diffraction fringes. Experiments were performed to validate these theoretical findings.
16 citations
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TL;DR: An appropriate formalism based on wave optics is introduced, which allows a particularly fast and simple correction of any interference based effects of Poly(methyl methacrylate) layers on silicon substrates and can be used as benchmark to test the performance of other methods for interference fringe removal.
Abstract: Substantial refractive index mismatches between substrate and layers lead to undulating baselines, which are known as interference fringes. These fringes can be attributed to multiple reflections inside the layers. For thin and plane parallel layers, these multiple reflections result in wave interference and electric field intensities which strongly depend on the location within the layer and wavenumber. In particular, the average electric field intensity is increased in spectral regions where the reflectance is reduced. Therefore, the most important precondition for the Beer-Lambert law to hold, absorption as the single reason for electric field intensity changes, is no longer valid and, since absorption is proportional to the electric field intensity, considerable deviations from the Beer-Lambert law result. Fringe removal is consequently synonymous with correcting deviations from the Beer-Lambert law in the spectra. Within this contribution, we introduce an appropriate formalism based on wave optics, which allows a particularly fast and simple correction of any interference based effects. We applied our approach for correcting transmittance spectra of Poly(methyl methacrylate) layers on silicon substrates. The interference effects were successfully removed and correct baselines, in good agreement with the calculated spectra, were obtained. Due to its sound theoretical foundation, our formalism can be used as benchmark to test the performance of other methods for interference fringe removal.
16 citations
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TL;DR: An accelerated ray-tracing algorithm is proposed to improve the computational efficiency of composite scattering from the 3-D ship target located on a random sea surface by using a new neighbor search technique, with a new 0–1 transformation rule and arrangement of octree nodes.
Abstract: This article proposes an accelerated ray-tracing algorithm to improve the computational efficiency of composite scattering from the 3-D ship target located on a random sea surface. The ray tracing is accelerated by using a new neighbor search technique, with a new 0–1 transformation rule and arrangement of octree nodes. It can reduce the code complexity and improve the computational efficiency. Combined with this technique, an accelerated algorithm based on the geometrical optics, physical optics with physical theory of diffraction (GO-PO/PTD) and capillary wave modification facet scattering model (CWMFSM) is further established. This is meaningful for the simulation of scattered echoes for wideband synthetic aperture radar (SAR), enabling SAR images to be formed using an imaging algorithm. The effectiveness of the proposed method was verified by comparing the simulation results with those produced by the FEKO-based multilevel fast multipole method (MLFMM). Further confirmation of its accuracy was obtained by comparing the simulated images with the measured ship image.
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TL;DR: In this paper, the convergence of the diffraction integral for gravitational lensing of GWs was investigated and the accuracy and efficiency of a number of numerical methods that can be used to calculate this integral, including integral mean method, asymptotic expansion method, Levin's method, zero points integral method, etc.
Abstract: Wave optics may need to be considered when studying the lensed waveforms of gravitational waves (GWs). However, the computation of the diffraction integral (amplification factor) in wave optics is challenging and time consuming. It is vital to develop an accurate and efficient method to calculate the amplification factor for detecting lensed GW systems. In this paper, we investigate the convergence of the diffraction integral for gravitational lensing of GWs and analyze the accuracy and efficiency of a number of numerical methods that can be used to calculate this integral, including the integral mean method, asymptotic expansion method, Levin's method, zero points integral method, etc. We further introduce a new method by combining the zero points integral and the asymptotic expansion methods to calculate the diffraction integral, which provides an efficient and accurate way to calculate the lensed waveform of GWs.
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TL;DR: A high-index contrast dielectric grating design for polarization-independent narrowband transmission filtering that provides a filter response that is simultaneously polarization independent and functional at normal incidence, overcoming limitations of 1D asymmetric gratings and 2D symmetric grating.
Abstract: We present a high-index contrast dielectric grating design for polarization-independent narrowband transmission filtering. A reduced symmetry hexagonal lattice allows coupling to symmetry-protected modes (bound states in the continuum) at normal incidence, enabling high-Q spectral peaks. The peak linewidth is tunable via degree of geometric symmetry reduction. Using diffraction efficiency calculations, we gain further insight into the design and physics of one-dimensional (1D) and two-dimensional (2D) asymmetric high contrast gratings. The grating design provides a filter response that is simultaneously polarization independent and functional at normal incidence, overcoming limitations of 1D asymmetric gratings and 2D symmetric gratings.
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TL;DR: In this article, the authors investigated the propagation of gravitational waves in wave optics, particularly focusing on the difference between their arrival time and the arrival time of light, and they argued that gravitational waves never arrive at an observer earlier than light when both gravitational waves and light are emitted from the same source simultaneously.
Abstract: It is known that geometrical optics no longer applies to the gravitational lensing if the wavelength of a propagating wave becomes comparable to or larger than the Schwarzshild radius of a lensing object. We investigate the propagation of gravitational waves in wave optics, particularly focusing on the difference between their arrival time and the arrival time of light. We argue that, contrary to the observation in the previous work, gravitational waves never arrive at an observer earlier than light when both gravitational waves and light are emitted from a same source simultaneously.
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Stockholm University1, Cornell University2, Pontifical Catholic University of Chile3, University of Pennsylvania4, University of California, Berkeley5, Princeton University6, University of Chicago7, University of Sussex8, University of California, San Diego9, Cardiff University10, Institute for the Physics and Mathematics of the Universe11, Arizona State University12, University of KwaZulu-Natal13, University of Milano-Bicocca14, Haverford College15, Lawrence Berkeley National Laboratory16, University of Melbourne17, Fermilab18, Goddard Space Flight Center19
TL;DR: Geometrical and physical optics simulation results for the Simons Observatory Large Aperture Telescope are presented and nonsequential ray tracing used to inform the design of the cold optics, including absorbers internal to each optics tube are described.
Abstract: We present geometrical and physical optics simulation results for the Simons Observatory Large Aperture Telescope. This work was developed as part of the general design process for the telescope; allowing us to evaluate the impact of various design choices on performance metrics and potential systematic effects. The primary goal of the simulations was to evaluate the final design of the reflectors and the cold optics which are now being built. We describe non-sequential ray tracing used to inform the design of the cold optics, including absorbers internal to each optics tube. We discuss ray tracing simulations of the telescope structure that allow us to determine geometries that minimize detector loading and mitigate spurious near-field effects that have not been resolved by the internal baffling. We also describe physical optics simulations, performed over a range of frequencies and field locations, that produce estimates of monochromatic far field beam patterns which in turn are used to gauge general optical performance. Finally, we describe simulations that shed light on beam sidelobes from panel gap diffraction.
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23 Apr 2020TL;DR: In this paper, a highly dispersive hologram is used together with a terahertz spectrometer to localize a corner-cube reflector placed in the region of interest.
Abstract: We present a new method to carry out localization based on distributed beamforming and neural networks. A highly dispersive hologram, is used together with a terahertz spectrometer to localize a corner-cube reflector placed in the region of interest. The transmission-type dielectric hologram transforms input pulse from the spectrometer into a complex pattern. The hologram causes complicated propagation paths which introduce delay so that different parts of the region of interest are interrogated in a unique way. We have simulated the emitted pulses propagating through the hologram. The hybrid simulation combines the finite-difference and physical optics methods in time domain and allows for evaluating the dispersion and directive properties of the hologram. The dispersive structure is manufactured of Rexolite and it has details resulting in varying delay from 1 to 19 wavelengths across the considered bandwidth. The spectrometer is configured in reflection mode with wavelets passing in to the region of interest through the hologram. A data-collecting campaign with a corner-cube reflector is carried out. The effective bandwidth for the localization is from 0.1 THz to 2.1 THz, and the measured loss is 57 dB at minimum. The collected data is used to train a fully-connected deep neural network with the known corner-cube positions as labels. Our first experimental results show that it is possible to predict the position of a reflective target in the region of interest. The accuracy of the prediction is 0.5-0.8 mm at a distance of 0.17 m.
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TL;DR: In this paper, a narrow surface element (NSE) method based on physical optics and physical theory of diffraction (PTD) is presented to improve the radar scattering characteristics of the target in the head direction.
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TL;DR: Coherent and partially coherent accurate wavefront propagation simulations using Synchrotron Radiation Workshop through thick two-dimensional Be compound refractive lenses are presented, taking into account the effects of phase errors obtained by X-ray speckle vectorial tracking at the BM05 Instrumentation Beamline at the ESRF.
Abstract: A framework based on physical optics for simulating the effect of imperfect compound refractive lenses (CRLs) upon an X-ray beam is described, taking into account measured phase errors obtained from at-wavelength metrology. A CRL stack is modelled, with increasing complexity, as a single thin phase element, then as a more realistic compound element including absorption and thickness effects, and finally adding realistic optical imperfections to the CRL. Coherent and partially coherent simulations using Synchrotron Radiation Workshop (SRW) are used to evaluate the different models, the effects of the phase errors and to check the validity of the design equations and suitability of the figures of merit.
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TL;DR: The phase-sensitive X-ray imaging technique based on the bilens interferometer allows acquiring the absolute value of a phase shift profile of the sample with a fairly high phase and spatial resolution.
Abstract: The phase-sensitive X-ray imaging technique based on the bilens interferometer is developed The essence of the method consists of scanning a sample, which is set upstream of the bilens across the beam of one lens of the interferometer by recording changes in the interference pattern using a high-resolution image detector The proposed approach allows acquiring the absolute value of a phase shift profile of the sample with a fairly high phase and spatial resolution The possibilities of the imaging technique were studied theoretically and experimentally using fibres with different sizes as the test samples at the ESRF ID06 beamline with 12 keV X-rays The corresponding phase shift profile reconstructions and computer simulations were performed The experimental results are fully consistent with theoretical concepts and appropriate numerical calculations Applications of the interferometric imaging technique are discussed, as well as future improvements
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TL;DR: In this article, the exact formulas for the induced electric surface current (in the scattering phenomenon) and the equivalent electric surface currents in the diffraction phenomenon on the open cylindrical surface due to an arbitrary narrow-band beam have been shown in their closed-form expressions within the context of the cylinear harmonics, which gives information about the validity of the Physical Optics (PO) approximation.
Abstract: The exact formulas for the induced electric surface current (in the scattering phenomenon) and the equivalent electric surface current (in the diffraction phenomenon) on the open cylindrical surface due to an arbitrary narrow-band beam have been shown in their closed-form expressions within the context of the cylindrical harmonics, which gives information about the validity of the Physical Optics (PO) approximation. Both the Electric Field Integral Equation (EFIE) and the Magnetic Field Integral Equation (MFIE) are used to find the induced (equivalent) electric surface currents in the context of the cylindrical harmonics. The numerical example of the scattering and diffraction of the Hermite Gaussian beam from the open cylindrical surface is shown. The result is useful for the evaluation of the validity of the PO approximation in the cylinder-like surface.
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TL;DR: In this article, it was shown that the classical and quantum dispersion relations are different due to the presence of the Bohm potential, and that the dispersion relation may also coincide when additional assumptions are made, such as WKB or eikonal approximations.
Abstract: It is showed that, in general, classical and quantum dispersion relations are different due to the presence of the Bohm potential. There are exact particular solutions of the quantum (wave) theory which obey the classical dispersion relation, but they differ in the general case. The dispersion relations may also coincide when additional assumptions are made, such as WKB or eikonal approximations, for instance. This general result also holds for non--quantum wave equations derived from classical counterparts, such as in ray and wave optics, for instance. Explicit examples are given for covariant scalar, vectorial and tensorial fields in flat and curved spacetimes.
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TL;DR: In this paper, the fast physical optics (FPO) method was proposed to calculate the scattered fields from the electrically large scatterers, where the quadratic patches were adopted to discretize the surfaces of the scatterer.
Abstract: In this article, we propose the fast physical optics (FPO) method to calculate the scattered fields from the electrically large scatterers. The quadratic patches are adopted to discretize the surfaces of the scatterers. Invoking the quadratic amplitude and phase functions approximations, the closed-form formulas could be obtained with the complementary error function. Hence, the FPO method is time-saving compared with the conventional methods. Moreover, the accuracy and the physical insight of the closed-form formulas are expounded. Numerical examples demonstrate the efficiency of the FPO method with respect to both the accuracy and CPU time.
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TL;DR: A realistic wave optics simulation method has been developed to study how wavefront distortions originating from heat load deformations can be corrected using adaptive X-ray optics.
Abstract: A realistic wave optics simulation method has been developed to study how wavefront distortions originating from heat load deformations can be corrected using adaptive X-ray optics. Several planned soft X-ray and tender X-ray insertion-device beamlines in the Advanced Light Source upgrade rely on a common design principle. A flat, first mirror intercepts the white beam; vertical focusing is provided by a variable-line-space monochromator; and horizontal focusing comes from a single, pre-figured, adaptive mirror. A variety of scenarios to cope with thermal distortion in the first mirror are studied by finite-element analysis. The degradation of the intensity distribution at the focal plane is analyzed and the adaptive optics that correct it is modeled. The range of correctable wavefront errors across the operating range of the beamlines is reported in terms of mirror curvature and spatial frequencies. The software developed is a one-dimensional wavefront propagation package made available in the OASYS suite, an adaptable, customizable and efficient beamline modeling platform.
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01 Feb 2020TL;DR: In this article, a split-step method was proposed to model the turbulence along the propagation path as a series of thin random phase screens with modified von Karman refractive index statistics using the Hufnagel-Valley turbulence profile.
Abstract: Modeling the effects of atmospheric turbulence on optical beam propagation is a key element in the design and analysis of free-space optical communication systems. Numerical wave optics simulations provide a particularly useful technique for understanding the degradation of the optical field in the receiver plane when the analytical theory is insufficient for characterizing the atmospheric channel. Motivated by such an application, we use a split-step method modeling the turbulence along the propagation path as a series of thin random phase screens with modified von Karman refractive index statistics using the Hufnagel-Valley turbulence profile to determine the effective structure constant for each screen. In this work, we employ a space-to-ground case study to examine the irradiance and phase statistics for both uniformly and non-uniformly spaced screens along the propagation path and compare to analytical results. We find that better agreement with the analytical theory is obtained using a non-uniform spacing with the effective structure constant for each screen chosen to minimize its contribution to the scintillation in the receiver plane. We evaluate this method as a flexible alternative to other standard layered models used in astronomical imaging applications.
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TL;DR: Physical simulation of optical measurement systems is focused on and the agreement of simulations with reality is a promising proof of concept for machine vision experts, to move towards automating the setup planning process by means of sensor-realistic simulations.
Abstract: Image acquisition plays a central role in optical measurement systems. To configure machine vision setups, engineers often go through some empirical best practices to evaluate the measurement in different geometrical and optical configurations. This approach turns out to be expensive, tedious, and sometimes even unsuitable for nontrivial tasks. To automate this process, realistic synthetic images allow us to evaluate and optimize imaging setups without employing physical parts and sensors. Available computer graphics rendering techniques can be very beneficial for realistic simulation of images in machine vision systems. Simulating optical measurement systems, however, requires taking extra simulation components into account, including the wave optics effects and realistic spectral response and stochastic noise of the digital sensor. In this article, we focus on physical simulation of optical measurement systems and further propose and verify a sensor-realistic simulation framework for this purpose. We demonstrate the results in different steps for a laser triangulation measurement system, and verify them against experimental images, both qualitatively and quantitatively. The measurement with a laser light source results in wave optics effects which cannot be modeled by conventional ray-tracing methods. The concepts of this article are, however, general to many optical systems with both coherent and/or incoherent light sources. The agreement of simulations with reality is a promising proof of concept for machine vision experts, to move towards automating the setup planning process by means of sensor-realistic simulations.
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TL;DR: In this paper, a two-lens high-density polyethylene (HDPE) $ f/1.6 $f/ 1.6 refractor design was compared to a similar twolens refractor using silicon lenses.
Abstract: We present a compact two-lens high-density polyethylene (HDPE) $ f/1.6 $f/1.6 refractor design that is capable of supporting a 28-deg diffraction-limited field of view at 1-mm wavelengths and contrast it to a similar two-lens refractor using silicon lenses. We compare the optical properties of these two systems as predicted by both geometrical and physical optics. The presented analysis suggests that by relaxing telecentricity requirements, a plastic two-lens refractor system can be made to have a surprisingly large field of view. Furthermore, this HDPE system is found to perform comparably to a similar silicon system across a wide field of view and wavelengths up to 1 mm. We show that for both telescope designs, cold stop spillover changes significantly across the field of view in a way that is somewhat inconsistent with Gaussian beam formalism and simple $ f $f-number scaling. We present results that highlight beam ellipticity dependence on both pixel location and pixel aperture size—an effect that is challenging to reproduce in standard geometrical optics. We show that a silicon refractor design suffers from larger cross-polarization compared to the HDPE design. Our results address the limitations of relying solely on geometrical optics to assess relative performance of two optical systems. We discuss implications for future refractor designs.
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TL;DR: In this paper, an inverse synthetic aperture radar (ISAR) imaging method using time-domain (TD) scattering echo simulated by timedomain physical optics (TDPO) method was proposed.
Abstract: In this letter, we propose an inverse synthetic aperture radar (ISAR) imaging method using time-domain (TD) scattering echo simulated by time-domain physical optics (TDPO) method. First, the TD pulse plane wave is taken as the incident wave and the transient scattering echo data matrix is obtained by using the TDPO method under different look angles of the target. Then, demodulation, pulse compression, and azimuth inverse fast Fourier transform (FFT) are performed on the echo data matrix to obtain the ISAR image under small bandwidth small angle. In this letter, considering the fact of TD pulse signals emitted by radar, electromagnetic scattering modeling method is adopted to obtain more accurate TD scattering echoes. This method combines the electromagnetic scattering algorithm and radar imaging algorithm effectively and is closer to practical application. Finally, ISAR images are given to verify the feasibility and fidelity of the presented method.
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TL;DR: In this article, a theory concerning scattering of electromagnetic (EM) waves with orbital angular momentum (OAM) is presented, in which a metallic sphere illuminated by OAM waves is adopted to simplify the study.
Abstract: In this letter, theory concerning scattering of electromagnetic (EM) waves with orbital angular momentum (OAM) is presented, in which a metallic sphere illuminated by OAM waves is adopted to simplify the study. Based on the series expansion and the physical optics (PO) methods, expressions of incident and scattered OAM waves are obtained. To get the expansion coefficients of the scattered fields, boundary conditions and Debye potentials are applied to establish the relationship between incident and scattered fields. Besides, a full EM wave simulation of the scattered field has been accomplished by the computer simulation technology (CST), the measurement of scattered field is done in an anechoic chamber. The simulated results are in good consistency with numerical calculations, demonstrating the interaction between the OAM EM waves and the metallic target sphere effectively. This letter also paves the way for research on scattering of complex targets of OAM waves, and for future studies on target detection.
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TL;DR: In this article, the authors present a methodology for non-scalar diffraction while maintaining the efficiency and ease of standard Fourier optics techniques, based on that of Braunbek, in which the Kirchhoff boundary values are replaced with the exact field in a narrow seam surrounding the edge of the diffracting element.
Abstract: Fourier optics is a powerful and efficient tool for solving many diffraction problems, but relies on the assumption of scalar diffraction theory and ignores the three-dimensional structure and material properties of the diffracting element. Recent experiments of sub-scale starshade external occulters revealed that the inclusion of these physical properties is necessary to explain the observed diffraction at 10−10 of the incident light intensity. Here, we present a methodology for implementing non-scalar diffraction while maintaining the efficiency and ease of standard Fourier optics techniques. Our methodology is based on that of Braunbek, in which the Kirchhoff boundary values are replaced with the exact field in a narrow seam surrounding the edge of the diffracting element. In this paper, we derive the diffraction equations used to implement non-scalar diffraction and outline the computational implementation used to solve those equations. We also provide experimental results that demonstrate our model can replicate the observational signatures of non-scalar diffraction in sub-scale starshades, in effect validating our model to better than 10−10 in relative intensity. We believe this method to be an efficient tool for including additional physics to the models of coronagraphs and other optical systems in which a full electromagnetic solution is intractable.
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TL;DR: In this article, a multilevel fast physical optics (MLFPO) method is proposed to accelerate the computation of the fields scattered from electrically large coated scatterers.
Abstract: The multilevel fast physical optics (MLFPO) is proposed to accelerate the computation of the fields scattered from electrically large coated scatterers. This method is based on the quadratic patch subdivision and the multilevel technology. First, the quadratic patches are employed rather than the planar patches to discretize the considered scatterer. Hence, the number of the contributing patches is cut dramatically, thus making the workload of the MLFPO method much lower than that of the traditional Gordon’s method. Next, the multilevel technology is introduced in this work to avoid calculating the physical optics scattered fields from the considered scatterer directly, so that the proposed algorithm can significantly reduce the computational complexity. Finally, numerical results have demonstrated the accuracy and efficiency of the MLFPO method based on the quadratic patches.