Showing papers on "Physical optics published in 1989"
TL;DR: In this article, a ray-shooting approach is presented for calculating the interior radar cross section (RCS) from a partially open cavity, where a dense grid of rays is launched into the cavity through the opening.
Abstract: A ray-shooting approach is presented for calculating the interior radar cross section (RCS) from a partially open cavity. In the problem considered, a dense grid of rays is launched into the cavity through the opening. The rays bounce from the cavity walls based on the laws of geometrical optics and eventually exit the cavity via the aperture. The ray-bouncing method is based on tracking a large number of rays launched into the cavity through the opening and determining the geometrical optics field associated with each ray by taking into consideration: (1) the geometrical divergence factor, (2) polarization, and (3) material loading of the cavity walls. A physical optics scheme is then applied to compute the backscattered field from the exit rays. This method is so simple in concept that there is virtually no restriction on the shape or material loading of the cavity. Numerical results obtained by this method are compared with those for the modal analysis for a circular cylinder terminated by a PEC plate. RCS results for an S-bend circular cylinder generated on the Cray X-MP supercomputer show significant RCS reduction. Some of the limitations and possible extensions of this technique are discussed. >
831 citations
01 May 1989
TL;DR: A summary of the development and verifications of a computer code, RECOTA (return from complex target), developed at Boeing Aerospace for calculating the radar cross section of complex targets is presented in this article.
Abstract: A summary of the development and verifications of a computer code, RECOTA (return from complex target), developed at Boeing Aerospace for calculating the radar cross section of complex targets is presented. The code utilizes a computer-aided design package for modeling target geometry in terms of facets and wedges. It is based on physical optics, physical theory of diffraction, ray tracing, and semiempirical formulations, and it accounts for shadowing, multiple scattering and discontinuities for monostatic calculations. >
195 citations
TL;DR: A modified Kirchhoff approximation (MKA) is developed for the scattering of light by randomly oriented crystals that contains a particle size dependence, which is not included in ray optics treatments, and satisfactory results can be obtained for size parameters larger than ten.
Abstract: A modified Kirchhoff approximation (MKA) is developed for the scattering of light by randomly oriented crystals. The reflected and transmitted near fields are calculated from ray tracing; the corresponding far fields are then obtained via the vector Kirchhoff integral. On the shadow side of the particle, an additional near field exactly cancels the incident field and causes the forward diffraction. MKA contains a particle size dependence, which is not included in ray optics treatments, and satisfactory results can be obtained for size parameters larger than ten. The scattering phase functions and degrees of linear polarization are calculated for some hexagonal and cubic water ice crystals using MKA. The Kirchhoff approximation for particles other than crystals is discussed, and attention is paid to the backscattering enhancement due to the cyclic passage of internally or multiply externally reflected electromagnetic waves.
119 citations
TL;DR: The scattering phase function and the degree of linear polarization for small crystals oriented randomly in space have been computed using the geometric ray tracing theory and assuming that the crystals are homogeneous and isotropic.
Abstract: The scattering phase function and the degree of linear polarization for small crystals oriented randomly in space have been computed using the geometric ray tracing theory and assuming that the crystals are homogeneous and isotropic. Calculations have been carried out for the main crystal geometries. Detection of halos from crystals other than hexagonal water ice is briefly discussed. The crystal size and shape parameters have also been averaged over some simple distributions in order to examine general light scattering properties of sharp-edged particles. A scalar physical optics correction has been developed for the geometric optics phase functions. Results can be applied to light scattering from regoliths and planetary rings, and possibly also to atmospheric halos. Retroreflecting crystals in the regolith would cause an opposition spike, a phenomenon observed for many bright satellites.
112 citations
TL;DR: In this paper, the single particle phase function and the linear polarization for large stochastically deformed spheres have been calculated by Monte Carlo simulation using the geometrical optics approximation, and applications of this theory to the photometric properties of atmosphereless bodies and interplanetary dust are discussed.
Abstract: The single particle phase function and the linear polarization for large stochastically deformed spheres have been calculated by Monte Carlo simulation using the geometrical optics approximation. The radius vector of a particle is assumed to obey a bivariate lognormal distribution with three free parameters: mean radius, its standard deviation and the coherence length of the autocorrelation function. All reflections/refractions which include sufficient energy have been included. Real and imaginary parts of the refractive index can be varied without any restrictions. Results and comparisons with some earlier less general theories are presented. Applications of this theory to the photometric properties of atmosphereless bodies and interplanetary dust are discussed.
86 citations
TL;DR: In this article, it was shown that the Hermite-Gauss-and Laguerre-type solutions of paraxial optics with complex arguments are closely related to a hidden symmetry in the parabolic equation.
Abstract: It is shown that the Hermite–Gauss- and Laguerre–Gauss-type solutions of paraxial optics whose corresponding Hermite and Laguerre polynomials have complex arguments are closely related to a hidden symmetry in the parabolic equation. These solutions are generated from the fundamental Gaussian beam solution by applying the powers of the infinitesimal operators of this symmetry group. The Fourier spectrum of these solutions is obtained from the Fourier spectrum of the fundamental Gaussian beam solution in a similar manner. The Gaussian beam solutions containing Hermite polynomials with complex arguments that were derived by Siegman [ J. Opt. Soc. Am.63, 1093 ( 1973)] represent a limiting case of the more-general solutions considered here. The generalized Gaussian beam solutions show a sharp mode picture with exact zeros in the field distribution only in the focal or waist plane. Unconventional applications of the parabolic approximation in optics including focus wave modes are demonstrated.
56 citations
01 May 1989
TL;DR: In this paper, the current-based hybrid formulation is summarized for classes of two-and three-dimensional scatterers for perfectly conducting, partially penetrable, and totally coated bodies.
Abstract: Depending on the angle of illumination, electrically large scatterers can support a variety of electromagnetic (EM) phenomena, such as traveling waves, creeping waves, and edge/surface diffraction effects. The electrical size of a body limits the tractability of numerical methods such as the method of moments (MM), and the geometric complexity of an object circumscribes the applicability of optics-derived methods. Hybrid methods incorporating both numerical and high-frequency asymptotic techniques have the potential to substantially enlarge the class of EM scattering problems that can be treated. In this discussion, the current-based hybrid formulation is summarized for classes of two- and three-dimensional scatterers. The use of Ansatz solutions derived from physical optics, the physical theory of diffraction, and the Fock theory is illustrated for perfectly conducting, partially penetrable, and totally coated bodies. For the latter, a generalization rooted in the impedance boundary (Leontovich) condition is used. Complementing these Ansatz solutions, the Galerkin representation is used for regions where the foregoing are computationally or physically intractable. The above cases are illustrated by representative solutions explicating the approach. >
48 citations
TL;DR: Grazing-incidence x-ray optics have been reviewed and shown to have several interesting properties as mentioned in this paper, including the ability to make use of multiple reflection of x rays, which is of interest in surface research, medicine, etc.
Abstract: Grazing-incidence x-ray optics is briefly reviewed and shown to have several interesting properties. Capillary focusing systems which make use of multiple reflection of x rays are described. This optics is of interest in surface research, medicine, etc.
01 Mar 1989
TL;DR: Reflectance models based on physical optics and geometrical optics are studied and a reflectance framework comprising three components is proposed: the diffuse lobe, the specular lobe, andThe specular spike is proposed.
Abstract: Reflectance models based on physical optics and geometrical optics are studied. Specifically, the authors consider the Beckmann-Spizzichino (physical optics) model and the Torrance-Sparrow (geometrical optics) model. These two models were chosen because they have been reported to fit experimental data well. Each model is described in detail, and the conditions that determine the validity of the model are clearly stated. By studying reflectance curves predicted by the two models, the authors propose a reflectance framework comprising three components: the diffuse lobe, the specular lobe, and the specular spike. The effects of surface roughness on the three primary components are analyzed in detail. >
TL;DR: A ray tracing technique is presented based on the fundamental laws of ray and wave optics; it has been used to calculate the scattering properties of hexagonal ice crystals and the anisotropy of the scattered radiation is clearly shown.
Abstract: A ray tracing technique is presented based on the fundamental laws of ray and wave optics; it has been used to calculate the scattering properties of hexagonal ice crystals. These crystals were assumed to be oriented preferably horizontal, and, therefore, the resulting phase functions have been plotted vs direction in 3-D space contrary to earlier calculations of other authors. The anisotropy of the scattered radiation is clearly shown; on the average the phase function varies over ~2 orders of magnitude. From these single scattering results the multiple scattering between various ice crystals has also been calculated.
TL;DR: In this paper, the authors discuss the instability and chaos in Quantum Optics, and propose a method to solve the problem of quantum instability and Chaos in quantum Optics (COCO).
Abstract: (1989). Instabilities and Chaos in Quantum Optics. Journal of Modern Optics: Vol. 36, No. 1, pp. 149-149.
TL;DR: In this paper, the authors consider a reflector antenna system, consisting of a point light source O, a reflecting surface F, and an object T in space, to be illuminated in this system.
Abstract: Consider a reflector antenna system, consisting of a point light source O, a reflecting surface F, and an object T in space, to be illuminated in this system. Under the assumptions of the geometric optics theory it is required to construct the surface F when the position of the light source and the object T are given, and the power distribution is a function prescribed in advance on T. In addition, the aperture of the incidence ray cone is also prescribed. Using differential geometric methods the author studies this inverse problem and obtains certain relations between elements of the system. In the radially symmetric case the author establishes conditions for existence and uniqueness of a solution to the problem.
TL;DR: In this article, the authors describe the non-imaging optics for flux concentration and discuss the developments in the geometrical optics and physical optics of concentrators, including the second-stage optics and truncation.
Abstract: Publisher Summary This chapter describes the nonimaging optics for flux concentration The chapter discusses the developments in the geometrical optics and physical optics of concentrators Two-dimensional systems using mirrors are designed as theoretically perfect concentrators Refracting elements play an auxiliary role in nonimaging concentrators 3D systems are concentrators with axial symmetry Reflecting surfaces are essential for achieving a near approach to ideal concentrator performance Refracting components play a useful part in making concentrators more compact and more convenient to combine with other optical elements The chapter discusses the second-stage optics and truncation The simplest nonspecular form of reflection is Lambertian, in which the angular distribution of the reflected light is that of black-body radiation for any angle of incidence The edge-ray principle and the associated idea of maximum slope have led to many useful concentrator designs, but they do not show how the jumble of rays from multiple reflections inside a concentrator eventually yields a Lambertian or near-Lambertian output The geometrical vector flux formalism helps to understand this process The chapter discusses the attempts that have been made to extend the ideas of nonimaging optics beyond the geometrical optics model
TL;DR: Stochastic optics allows predictions for the empirical correlations very close, but not identical, to the quantum ones, and the theory is applied to the analysis of all experiments designed to test the Bell inequalities by measuring polarization correlations of photon pairs.
Abstract: Stochastic optics may be considered as simply a local realistic interpretation of quantum optics and, in this sense, it is a first step in the reinterpretation of the whole of quantum theory. However, as it is not possible to interpret all the details of quantum theory in a local realistic manner, as shown by Bell's theorem, minor changes are introduced in the formalism with the consequence that the new theory makes different predictions in some special cases. In stochastic optics, the quantum-operator formalism is simply considered a formal way of dealing with stochastic fields. In particular, the quantum zero point is taken as a real random electromagnetic radiation filling the whole of space. This radiation noise has the same nature as light signals, the only difference being the greater intensity of the latter. We assume that photon detectors have an intensity threshold just above the level of the noise, thus detecting only signals. Transmission of radiation through polarizers follows Malus's law, but the interplay of signal and noise leads quite naturally to the prediction that the detection probability of some signals is enhanced, which is known to be a necessary condition for the violation of the empirically tested Bell inequalities. In our view, correlated photon pairs are pairs of light signals supercorrelated in polarization, in the sense that, as well as the signal, the accompanying noise is also correlated. Thus stochastic optics allows predictions for the empirical correlations very close, but not identical, to the quantum ones. The theory is applied to the analysis of all experiments designed to test the Bell inequalities by measuring polarization correlations of photon pairs. The predictions agree with quantum optics and experiments within statistical errors, except for the Holt-Pipkin experiment. In this case, the experimental results agree with stochastic optical predictions within two standard deviations while violating quantum optics by four.
TL;DR: In this article, a multislice theory is proposed to solve Yoshioka's coupling equations for elastic and inelastic scattered high-energy electrons in a solid, which is capable of including the non-periodic crystal structures and the electron multiple scattering among all the excited states in the calculations.
Abstract: A multislice theory is proposed to solve Yoshioka's coupling equations for elastic and inelastic scattered high-energy electrons in a solid. This method is capable, in principle, of including the non-periodic crystal structures and the electron multiple scattering among all the excited states in the calculations. It is proved that the proposed theory for calculating the energy-filtered inelastic images [Wang (1989). Acta Cryst. A45, 193-199], based on the physical optics approach, is equivalent to the quantum-mechanical theory under some approximations. The basic theory of simulating the energy-filtered inelastic image of core-shell losses and thermal diffuse scattering is outlined.
Proceedings Article•
01 Jan 1989TL;DR: In this paper, a simple and efficient method for predicting the scattering of a leaf at millimeter wave frequencies was proposed, where the volume polarization current was approximated by the current which would exist in an infinite dielectric slab with the same profile.
Abstract: At millimeter wave frequencies a typical leaf is a significant fraction of a wavelength in thickness, and its nonuniform dielectric profile now affects the scattering. To provide a simple and efficient method for predicting the scattering, two types of physical optics approximations are examined. The first approximates the volume polarization current by the current which would exist in an infinite dielectric slab with the same profile, while the second (and simpler) one employs the surface current which, on the infinite slab, produces the known reflected field. It is shown that the first method is superior, and, provided the actual dielectric profile is used, it predicts the scattered field to an accuracy which is adequate for most practical purposes.
TL;DR: In this paper, a dual-reflector feed for the spherical reflector antenna in Arecibo is presented, which is analyzed over a large frequency range: at the lower frequencies by physical optics (PO) integration, and at the higher ones by a geometrical optic (GO) ray tracing technique described in another work.
Abstract: A proposed dual-reflector feed for the spherical reflector antenna in Arecibo is presented. This is analyzed over a large frequency range: at the lower frequencies by physical optics (PO) integration, and at the higher ones by a geometrical optic (GO) ray tracing technique described in another work. The latter calculations are extended with the transition region theory (TRT) to include edge diffraction. The results clearly demonstrate the usefulness of the time efficient TRT method. However, they also show that PO integration is important, as this has detected an underillumination of the central region of the aperture. This effect is related to a similar problem with the line feeds, but can in the present case be reduced by moving the subreflectors away from the paraxial focus.
01 Oct 1989
TL;DR: In this article, a geometrical optics approximation for waves in inhomogeneous chiral media is introduced based on the concept of normalized wave fields, which are certain complex combinations of the electric and magnetic fields, uncoupled for sufficiently slowly varying media.
Abstract: Geometrical optics approximation for waves in inhomogeneous chiral media is introduced based on the concept of normalized wave fields, which are certain complex combinations of the electric and magnetic fields, uncoupled for sufficiently slowly varying media. For small values of the chirality parameter, the geometrical optics rays can be calculated as for a chiral media and the main effect of the chirality is rotation of polarization along the ray. Thus, adding chirality to inhomogeneous lens antennas, their polarization properties can be improved. As an example, it is demonstrated how the inherent cross polarization of the Maxwell fish-eye lens is compensated through a suitable chirality distribution.
TL;DR: In this article, a physical interpretation of each term in the full-wave expansion of the vertically or horizontally polarized electromagnetic fields scattered by irregular stratified media is given, which provides a basis for the construction of physical models of nonspecular scatter in complex, irregular, layered structures.
Abstract: A physical interpretation is given of each term in the full-wave expansion of the vertically or horizontally polarized electromagnetic fields scattered by irregular stratified media. These solutions provide a basis for the construction of physical models of nonspecular scatter in complex, irregular, layered structures. The full wave solutions involve a pair of nonspecular reflection scattering coefficients and a pair of nonspecular transmission scattering coefficients that reduce to the familiar Fresnel reflection and transmission coefficients for the specular case. The full-wave solutions are shown to satisfy the reciprocity and duality relationships in electromagnetic theory, and they are invariant to coordinate transformations. The relationships between the full-wave solution, the high-frequency physical optics solution, and the low-frequency perturbation solution are demonstrated. The analysis is relevant to problems of communication in irregular stratified media and to problems of remote sensing. >
TL;DR: In this paper, an exact matrix optical propagator, in inhomogeneous media, is evaluated by the path integral formalism using an exact summation of the Feynman-Dyson perturbation series in the paraxial approximation.
TL;DR: In this article, a simplified method of estimating the equivalent surface resistance of a reflecting mesh is presented, which is obtained from the approximate mesh reflection coefficients, which are based on averaged boundary conditions, allowing an integral equation solution for the mesh reflector that is a simple extension of that for the perfectly conducting reflector.
Abstract: A simplified method of estimating the equivalent surface resistance of a reflecting mesh is presented. The equivalent resistance is obtained from the approximate mesh reflection coefficients, which are based on averaged boundary conditions. This resistance approximation allows an integral equation solution for the mesh reflector that is a simple extension of that for the perfectly conducting reflector. Paraboloid radiation patterns using physical optics in conjunction with the reflection coefficients are compared to an E-field integral equation solution for a resistive surface. The agreement is excellent for low to moderate resistance values, even in the sidelobe regions. >
TL;DR: In this article, a technique referred to as the on-surface radiation boundary condition (OSR) approach is applied to a variety of two-dimensional imperfectly conducting geometries.
Abstract: A technique referred to as the on-surface radiation boundary condition (OSR) approach is applied to a variety of two-dimensional imperfectly conducting geometries. Specifically, analytical solutions and numerical data are presented for the scattering by elliptical and rectangular cylinders and restrictive strips. These are then compared with calculations using the traditional physical optics (PO) approximation and moment method (MM). Emphasis is on the accuracy afforded by using OSRC as opposed to the MM or PO formulations. >
TL;DR: In this paper, a theory of many-wave optics of cholesteric blue phases is developed, and the solution of the phase problem (i.e., the determination of the relative phases of the Fourier harmonics of the blue-phase order parameter) by means of many wave diffraction is discussed.
Abstract: A theory of many-wave optics of cholesteric blue phases is developed. The solution of the phase problem (i.e. the determination of the relative phases of the Fourier harmonics of the blue-phase order parameter) by means of many-wave diffraction is discussed. In the framework of many-wave blue-phase optics, the experimentally observed intensities of the Kossel lines are described. It is shown that the (111) and (200) Bragg reflections, observed in BPII, may be caused by coherent multiple diffraction.
TL;DR: In this article, the exact moment method (PO) was compared with the moment method solution based on the impedance boundary condition for the case of the coated cone-sphere, which consistently gives the best numerical results.
Abstract: The familiar physical optics (PO) approximation is no longer valid when the perfectly conducting scatterer is coated with dielectric material. This paper reviews several possible PO formulations. By comparing the PO formulation with the moment method solution based on the impedance boundary condition for the case of the coated cone-sphere, a PO formulation using both electric and magnetic currents consistently gives the best numerical results. Comparisons of the exact moment method with the PO formulations using the impedance boundary condition and the PO formulation using the Fresnel reflection coefficient for the case of scattering from the cone-ellipsoid demonstrate that the Fresnel reflection coefficient gives the best numerical results in general.
20 Jun 1989
TL;DR: In this paper, the shape of CO2 laser beam by Kaleidoscope was analyzed by geometrical and physical optics, and the effects of angular and positional misalignments of the optics with respect to laser beam axis were discussed.
Abstract: Shaping of CO2 laser beam by Kaleidoscope, in which uniform intensity is obtained by multiple reflections, is analyzed by geometrical and physical optics. Gaussian beam is transformed into square beam spot with nonuniformity less than 2% when the beam reflects 2-3 times. Effects of angular and positional misalignments of the optics with respect to laser beam axis are also discussed. Through the analysis of the beam shaping, a novel optics has been developed, which produces rectangular-Gaussian beam spot with variable aspect ratio, unlike the case of Kaleidoscope where the aspect ratio of the beam spot is unchangeable. This optics provides higher efficiency of beam shaping and higher absorption in metal working by utilizing plane-polarized laser beam. Laser-surface hardening is demonstrated without absorption coating by using this optics.