Showing papers on "Physical optics published in 1993"
TL;DR: Wave interactions, like diffraction and scattering, over the propagation path are described by the uniform theory of diffraction (UTD) and physical optics (PO) and models for rural and urban areas are presented for 2-D and 3-D ray tracing.
Abstract: Mobile communication links are severely influenced by propagation effects. Wave propagation in the VHF/UHF frequency range over natural and man-made terrain is strongly dependent on topography and morphography. Propagation modeling is based on a ray-optical approach. Wave interactions, like diffraction and scattering, over the propagation path are described by the uniform theory of diffraction (UTD) and physical optics (PO). Propagation models for rural and urban areas are presented for 2-D and 3-D ray tracing. Near-range models apply to the corresponding areas in forest and urban sites. The field-strength delay spectrum describes ray contributions with deterministic amplitudes but statistical phases are used to derive time-and frequency-domain channel characteristics. Comparisons between measured and predicted data are presented. >
218 citations
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TL;DR: In this article, the Gaussian beam-mode treatment of free-space propagation is extended to cover the transformations produced by conic-section reflectors or lenses, and both the propagation steps and the lens transformations are incorporated into a matrix formulation readily applicable to networks of such reflectors.
Abstract: The basis of the near-complete analytical methodology that now exists for the design of long-wave optical systems is set out. The Gaussian beam-mode treatment of free-space propagation is extended to cover the transformations produced by conic-section reflectors or lenses, and both the propagation steps and the lens transformations are incorporated into a matrix formulation readily applicable to networks of such reflectors or lenses. In the process the theorems of Fourier optics are demonstrated and the vectorial properties of the beam-fields are kept explicit. It is shown how recent formulations of partial coherence have made it possible to include partially coherent beams in the same methodology. For the design of high-performance systems, the inclusion of higher-order mode dispersion must be fully understood, the vector properties must be recoverable, and the paraxiality on which the methodology rests must be critically assessed. The authors emphasize these aspects and present a single systematic formulation embracing all the elements. >
115 citations
TL;DR: The sensitivity of the single-mode receiver surpasses that of a classical two-pinhole setup with a coherence factor of 0.8 by a factor of 4 and the advantage increases rapidly when a still higher coherence factors is desired.
Abstract: Single-mode optical fibers provide the ideal receiver optics for dynamic light-scattering measurements. Theoretical analysis shows that with a single-mode fiber one can achieve a theoretical limit of 1 for the coherence factor while maintaining a high light-collection efficiency. In fact, the sensitivity of the single-mode receiver surpasses that of a classical two-pinhole setup with a coherence factor of 0.8 by a factor of 4 and the advantage increases rapidly when a still higher coherence factor is desired. In addition, a single-mode fiber receiver offers the possibility of working with an arbitrary large scattering volume and with an arbitrary working distance. All these features are also demonstrated experimentally by a remarkably simple apparatus that consists, essentially, of a commercial laser beam delivery assembly.
111 citations
01 Dec 1993
TL;DR: In this article, the authors present an overview of a number of asymptotic and hybrid methods used to compute the radar cross section of objects that are large compared to the wavelength of the incident wave, and the effect of coating perfectly conducting bodies with dielectric materials.
Abstract: Asymptotic and hybrid methods are widely used to compute the Radar Cross Section (RCS) of objects that are large compared to the wavelength of the incident wave, and the objective of this paper is to present an overview of a number of these methods. The cornerstone of the asymptotic methods is the Geometrical Theory of Diffraction (GTD), which was originally introduced by J. B. Keller, and which represents a generalization of the classical Geometrical Optics (GO) by virtue of the inclusion of diffraction phenomena. After a presentation of the physical principles of GTD, we provide a description of its mathematical foundations. In the process of doing this we point out that GTD gives inaccurate results at caustics and light-shadow boundaries, and subsequently present a number of alternate approaches to dealing with these problems, viz., Uniform theories; Methods for caustics curves; Physical Theory of Diffraction; and Spectral Theory of Diffraction. The effect of coating perfectly conducting bodies with dielectric materials is discussed and hybrid methods, that combine the Method of Moments (MoM) with asymptotic techniques, are briefly reviewed. Finally, the application of GTD and related techniques is illustrated by considering some representative radar targets of practical interest. >
78 citations
TL;DR: In this article, the authors combine near-infrared intensity-modulated illumination with frequency domain detection methods to obtain the first detailed optical images of thick tissues (1-3 cm), which are characterized by millimetre resolution and high contrast.
Abstract: By combining near-infrared intensity-modulated illumination with frequency domain detection methods, we have obtained the first detailed optical images of thick tissues (1–3 cm). The raw data of these images are characterized by millimetre resolution and high contrast. The method employs a pulsed laser coupled to a cross-correlation frequency domain detection scheme. The near-infrared imaging method is non-invasive and inexpensive, uses non-ionizing radiation and is potentially fast enough for real-time imaging in the seconds time range. In the frequency domain, diffusional wave optics provides the framework for a description of the light propagation in tissues. Our approach results in a theoretically and experimentally simple way to exploit the advantages of time resolution in optical imaging of inhomogeneous highly scattering materials. At any given modulation frequency, the light wavefront advances at constant velocity in a spherical wave. Objects with scattering or absorption coefficients that are different from the surrounding medium cause a deformation of the propagating wavefront that can be accurately measured using frequency domain detection methods. The visualization (on a computer screen) of these wavefront deformations provides a projection of the interior's image.
75 citations
50 citations
TL;DR: In this paper, the authors considered the case of a uniform medium and proposed a new distribution function which is exactly conserved along the rays of the Wigner function and the integral transform along the real and the imaginary parts of Walther's distribution function.
Abstract: Corrections to classical radiometry are considered for the case of a uniform medium. The corrections represent wave effects of physical optics and of the effects of partial coherence. New results include integral transforms and infinite series connecting the real and the imaginary parts of Walther’s distribution function and the Wigner function, infinite series representing all the corrections to the evolution of different distributions along rays, and estimates and comparisons of the degree to which different distribution functions are conserved along rays. In addition, a new distribution function is presented, which is exactly conserved along rays.
49 citations
Journal Article•
TL;DR: In this article, a geometrical point spread function (PSF) model is used in place of the physical PSF model when the SNR is less than 30 dB.
Abstract: Point spread function (PSF) models derived from physical optics provide a more accurate representation of real blurs than simpler models based on geometrical optics. However, the physical PSF models do not always result in a significantly better restoration, due to the coarse sampling of the recording device and insufficiently high signal-to-noise ratio (SNR) levels. Low recording resolutions result in aliasing errors in the PSF and suboptimal restorations. A high-resolution representation of the PSF where aliasing errors are minimized is used to obtain improved restorations. The SNR is the parameter which ultimately limits the restoration quality and determines the need for an accurate PSF model. As a rule of thumb, the geometrical PSF can be used in place of the physical PSF without significant loss in restoration quality when the SNR is less than 30 dB.
45 citations
TL;DR: Theoretically, the idea of electron holography is straightforward: the electron image wave is recorded in a hologram and reconstructed by subsequent processing according to the laws of wave optics.
45 citations
TL;DR: Numerical methods and tools from physical optics are used further to characterize the influences of the grating, light parameters, and the position of the plane of observation on pattern form, fine structure, band positions, and phases, and it is found that none of the patterns in the Talbot planes actually approximates grating images in terms of all of these properties.
Abstract: It has been widely said that with the Talbot effect a grating makes images of itself unaided. However, the effect as produced by simple amplitude gratings was recently redefined in terms of interference-pattern visibility or contrast instead of self-imaging. Then, by starting with a pair of slits instead of the usual infinite grating, a new and more general description of the effect was developed. Now numerical methods and tools from physical optics are used further to characterize the influences of the grating, light parameters, and the position of the plane of observation on pattern form, fine structure, band positions, and phases. It is found that none of the patterns in the Talbot planes actually approximates grating images in terms of all of these properties. Hence the Talbot effect should be defined in terms of interference effects, not grating images.
TL;DR: In this article, the effect of cracks on the surface of reflectors that can result from the imperfect fitting together of panels to form large reflectors was investigated. But the results were limited to three models of cracks, and significant pattern effects were found, depending on the model and orientation of the cracks.
Abstract: Incremental length diffraction coefficients (ILDCs) for the half-plane are integrated around the rim of a paraboloid reflector antenna to obtain well-behaved far fields of the nonuniform current for all angles of observation. These far fields, when added to the physical optics far field, produce a more accurate total far field of the reflector. Excellent agreement with the far fields obtained from a method-of-moments solution to the electric field integral equation applied to a 20-wavelength-diameter reflector shows that the cross polarization, farther-out sidelobes, and fields near nulls of reflector antennas can be appreciably modified by the fields of the nonuniform currents. ILDCs are also used to investigate the effect of cracks on the surface of reflectors that can result from the imperfect fitting together of panels to form large reflectors. Three models of cracks are studied. Significant pattern effects are found, depending on the model and orientation of the cracks. >
TL;DR: In this article, the basic principle, methodology, and experimental results for frequency-swept microwave imaging of continuous shape conducting and discrete line objects in a bistatic scattering arrangement are presented.
Abstract: The basic principle, methodology, and experimental results for frequency-swept microwave imaging of continuous shape conducting and discrete line objects in a bistatic scattering arrangement are presented. The theoretical analysis is developed under the assumptions of plane wave illumination and physical optics approximation. The measurement system and calibration procedures are implemented based on plane wave spectrum analysis. Images of three different types of scattering objects reconstructed from the experimental data obtained in the frequency range 7.5-12.5 GHz are shown to be in good agreement with the scattering object geometries. The results demonstrate that this bistatic frequency-swept microwave imaging system has potential as a cost-effective tool for remote sensing, imaging radar, and nondestructive evaluation. >
TL;DR: In this article, a close comparison between special relativity and optics of stratified planar media is presented, which may provide some useful tools in optics, can also suggest interesting thoughts and questions both in optics and in special relativity, and in quantum theory.
Abstract: A close comparison is presented between special relativity and optics of stratified planar media. This presentation, which may provide some useful tools in optics, can also suggest interesting thoughts and questions both in optics, in special relativity, and in quantum theory.
TL;DR: In this article, the second-order small slope approximation for acoustic or TE-polarized electromagnetic scattering from one-dimensional, "Pierson-Moskowitz" sea surfaces at low grazing angles is presented.
Abstract: First- and second-order reflection coefficients are presented for the small slope approximation. The first-order reflection coefficient is identical to the Kirchhoff, or physical optics, result, and the second-order reflection coefficient reduces to those of perturbation theory and the Kirchhoff approximation in the appropriate limits. Numerical results are obtained for acoustic or TE-polarized electromagnetic scattering from one-dimensional, "Pierson-Moskowitz" sea surfaces at low grazing angles. Comparison with exact integral equation results shows that the second-order small slope approximation is extremely accurate and better than both the perturbation and Kirchhoff methods. >
TL;DR: Based on the theory of partially coherent light, an analytical scheme is established to determine the radiative properties of multilayer thin films in this paper, where the complex degree of coherence provides a direct measure of the varying influence of interference effects on spectral measurements.
Abstract: Based on the theory of partially coherent light, an analytical scheme is established to determine the radiative properties of multilayer thin films. Accurate knowledge of the magnitude of interference effects is absolutely indispensable when measurements of the spectral transmissivity and reflectivity of thin films are used to derive optical constants of the film material. As illustrated by experiments, in many cases of practical interest neither a geometrical nor a wave-optics model gives satisfactory results. A general formulation is introduced that covers this intermediate partially coherent regime as well as the limiting cases of geometrical and wave optics. The complex degree of coherence provides a direct measure of the varying influence of interference effects on spectral measurements. An analytical approximation of the numerical approach is developed that gives a good physical understanding of the occurring phenomena. Experiments on the transmissivity of a one-layer glass film using a Fourier transform infrared spectrometer in the medium infrared range (λ = 2 to 20 μm) confirm the theoretical approach and the relevance of the addressed issue.
TL;DR: Wave-optics calculations of the temporal and spatial evolution from random noise of a double phase-conjugate mirror in photorefractive media that show its image exchange and phase-reversal properties show that for values of coupling coefficient times length greater than two the process exhibits excellent conjugation fidelity, behaves as an oscillator, and continues to operate even when the noise required for starting it is set to zero.
Abstract: We present wave-optics calculations of the temporal and spatial evolution from random noise of a double phase-conjugate mirror in photorefractive media that show its image exchange and phase-reversal properties. The calculations show that for values of coupling coefficient times length greater than two the process exhibits excellent conjugation fidelity, behaves as an oscillator, and continues to operate even when the noise required for starting it is set to zero. For values less than two, the double phase-conjugation process exhibits poor fidelity and disappears when the noise is set to zero.
28 Jun 1993
TL;DR: In this paper, the theoretical basis, relative accuracy, and limitations of dielectric physical optics (physical optics) are discussed, and example calculations are compared with numerically exact results obtained using the moment method in order to determine the accuracy of the PO approximation for several canonical problems.
Abstract: The theoretical basis, relative accuracy, and limitations of dielectric PO (physical optics) are discussed. Example calculations are compared with numerically exact results obtained using the moment method in order to determine the accuracy of the PO approximation for several canonical problems. The example calculations indicate that dielectric PO provides surprisingly good results for thin dielectric sheets. This method is very useful for situations involving relatively large curved dielectric shells provided multiple reflection effects are taken into account. The most significant inherent limitation involves grazing incidence. >
TL;DR: In this article, the loss characteristics in multimode transmission were studied for hollow waveguides, and simple equations for optical power attenuation were derived by the electromagnetic wave theory and the geometrical optics theory coincide exactly.
Abstract: The loss characteristics in multimode transmission were studied for hollow waveguides, and simple equations for optical power attenuation were derived. The equations that were derived by the electromagnetic wave theory and the geometrical optics theory coincide exactly. If the transmission loss is small, the optical power attenuates exponentially with the length of the waveguide. The transmission loss increases in proportion to the inverse of the bore radius and the square of the launch angle. The theoretical values that were calculated by the present equations were in good agreement with the data measured for the SiO2 and ZnSe-coated Ag hollow waveguides.
TL;DR: In this article, a nonisotropic scattering model is proposed to estimate the light absorption rates in a heterogeneous photoreactor containing plant cells of Coffea arabica and is compared with an isotropic scattering model.
Abstract: A nonisotropic scattering model is proposed to estimate the light absorption rates in a heterogeneous photoreactor containing plant cells of Coffea arabica and is compared with an isotropic scattering model. In order to determine the directions of noniso-tropically scattered light, optical theorems (geometrical optics and wave optics) are applied to light scattering caused by a homogeneous and perfect sphere. Two parameters, relative refractive index and attenuation coefficient, are used to characterize the ideal sphere. The primary feature of this model is that various phenomena of light scattering and absorption can be simulated by the combination of the two parameters. A measuring system composed of parallel plates was developed for evaluating the model. The nonisotropic scattering model was successfully applied to the heterogeneous reactor with the cultured plant cells.
TL;DR: It is shown that, under normal laboratory conditions and in the Fraunhofer approximation, the directional spectrum of light does not change on propagation in free space, and that each frequency component of the total spectrum is preserved in accordance with the principle of energy conservation.
Abstract: This paper attempts to reconcile conflicting points of view of laboratory physicists and coherence theorists on correlation-induced spectral changes arising from the partial coherence of primary and secondary light sources. It is shown that, under normal laboratory conditions and in the Fraunhofer approximation, the directional spectrum of light does not change on propagation in free space, and that each frequency component of the total spectrum is preserved in accordance with the principle of energy conservation. It is demonstrated, and illustrated by examples, that descriptions of diffraction by the theory of partial coherence and by classical wave optics are fully equivalent for incoherent primary sources. A statistical approach is essential, and coherence theory is required, for partially coherent primary sources.
TL;DR: In this paper, a uniform physical optics (PO) solution, valid across the reflection limits, is derived, derived from an asymptotic evaluation of the PO integral, including end-point contributions that account for the diffracted field on edges.
Abstract: The plane wave backscattering from a perfectly conducting three-dimensional shell of arbitrary cross section has peen studied. A uniform physical optics (PO) solution, valid across the reflection limits, is derived. The solution, derived from an asymptotic evaluation of the PO integral, includes end-point contributions that account for the diffracted field on edges. It can be improved by the fringe fields derived from an analytical integration of the equivalent edge currents of the physical theory of diffraction (PTD). It is computationally efficient for electrically large shells and compares very well with the finite-element method. >
05 Jan 1993
TL;DR: In this article, a rigorous electromagnetic diffraction theory of gratings is applied to predict the limits of the approximate theory, and to analyze and design diffractive microelements that can be treated only within the framework of the rigorous theory.
Abstract: As a result of the continuously improving resolution of the VLSI-based micro-optic fabrication technology, diffractive optical elements can now be manufactured that no longer obey the usual physical optics boundary conditions and the paraxial Fresnel and Fraunhofer diffraction integrals. Rigorous electromagnetic diffraction theory of gratings is applied here to predict the limits of the approximate theory, and to analyze and design diffractive microelements that can be treated only within the framework of the rigorous theory.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
TL;DR: In this paper, an eigenfunction expansion for the scattering pattern of a perfectly conducting strip and experimental bistatic scattering measurements of rectangular plates are used to verify the deviations from Snell's law.
Abstract: Snell's law of reflection applies to a plane wave incident on an infinite surface. For finite surfaces the size of the surface, the angle of incidence, and the polarization of the incident wave all contribute to deviations from Snell's law. An eigenfunction expansion for the scattering pattern of a perfectly conducting strip and experimental bistatic scattering measurements of rectangular plates are used to verify the deviations. Physical optics calculations also predict these deviations and are used to provide a physical explanation for the deviations. >
Journal Article•
TL;DR: Deflexion d'un faisceau laser par passage de celui-ci dans une zone a gradient de temperature (dans l'air).
Abstract: Deflexion d'un faisceau laser par passage de celui-ci dans une zone a gradient de temperature (dans l'air). Cette zone est produite par un second laser irradiant une surface d'acier
TL;DR: In this paper, the authors present a uniform physical optics (UPO) solution which remains valid at caustics occurring when two or more specular points coalesce at the inflection point of the S-shaped surface.
Abstract: When an S-shaped surface possesses no derivative discontinuities, techniques such as the geometrical theory of diffraction are not applicable. However, if the radius of curvature is relatively large at every point on the surface, the physical optics approximation may be employed. The authors present a uniform physical optics (UPO) solution which remains valid at caustics occurring when two or more specular points coalesce at the inflection point of the S-shaped surface. The solution is developed by approximating the surface with a localized cubic expansion, leading to exact expressions in terms of Airy integrals. In contrast to other solutions, the one given here requires only a knowledge of the stationary phase points and the first three derivatives of the surface-generating function at those points. A major effort is devoted to the validation of the UPO solution, and this is accomplished with numerical models of the S-shaped surface. It is found that the given UPO solution is quite accurate in the specular and nonspecular regions. >
TL;DR: In this paper, a mathematical model for the evaluation of the backscattering by a perfectly conducting 90° dihedral corner has been developed by adding the Physical Theory of Diffraction (PTD) correction term to the Improved Physical Optics (IPO) model, which takes into account also the lighting of each face by the rays diffracted from the edge of the other one.
Abstract: A very accurate mathematical model for the evaluation of the backscattering by a perfectly conducting 90° dihedral corner has been developed. It has been obtained by adding the Physical Theory of Diffraction (PTD) correction term to the Improved Physical Optics (IPO) model, which takes into account also the lighting of each face by the rays diffracted from the edge of the other one. The agreement of such a model with the experimental results has been found very good.
TL;DR: In this article, a model of spontaneous Brillouin scattering in the presence of a high power pump beam was developed and incorporated into a wave optics model of backward stimulated scattering, providing a realistic distributed noise source for numerical evaluation of the stimulated process.
Abstract: A model of spontaneous Brillouin scattering in the presence of a high power pump beam has been developed and incorporated into a wave optics model of backward stimulated Brillouin scattering, providing a realistic distributed noise source for the numerical evaluation of the stimulated process. The model is used to assess the location of the dominant noise contributions in determining the reflectivity and conjugation fidelity of the Stokes return. The effect of f-number and power over threshold is evaluated. The model is validated with experimental data on threshold and conjugation fidelity in the presence of a pump beam with a periodic phase aberration. >
TL;DR: The ray form of Newton's law of motion is derived in three different ways and is applied in the solution of several problems as mentioned in this paper, such as the problem of finding a ray in the gradient-index media.
Abstract: Through the use of the optical‐mechanical analogy, Newton’s law of motion may be cast into the same form as the equation for the ray in the geometrical optics of gradient‐index media. The resulting equation is called the ray form of Newton’s law of motion. The same equation may be derived by taking the geometrical optics limit of quantum mechanics. The ray form of Newton’s law of motion is derived in three different ways and is applied in the solution of several problems.
TL;DR: In this article, the optimal aperture and the minimum probe radius in low-voltage scanning electron microscopes (LVSEMs) were derived using both wave optics and geometric optics, and the computed results indicated the possibility of achieving 1·5-2·0-nm resolution at low voltages.
Abstract: Summary
Detailed investigating into the effects of spherical and chromatic aberrations, diffraction and the probe current allows the more general formulae for the optimized aperture and the minimum probe radius in low-voltage scanning electron microscopes (LVSEMs) to be derived using both wave optics and geometric optics. The probe sizes for a diversity of electron sources in LVSEMs have been estimated, which may be useful for practical applications. The computed results indicate the possibility of achieving 1·5–2·0-nm resolution at low voltages.