Showing papers on "Physical optics published in 1997"

I: The Wigner Distribution Function in Optics and Optoelectronics

Abstract: Publisher Summary The Wigner distribution function (WDF) in quantum mechanics is a mathematical tool that correctly yields the expectation values of any function of the coordinates or the momenta. The chapter discusses WDF applications to the characterization of light fields and optical systems and to the problem of coupling optimization between sources and waveguides. Phenomena such as diffraction, interference, coherence, or polarization cannot be managed in the framework of geometrical optics but only within wave optics, where the light field is characterized by a vectorial distribution that satisfies the Helmholtz equation. The applications of the WDF support the assertion that the WDF is a valuable theoretical and experimental tool in optics and optoelectronics. Further expansion of WDF applications will probably result from the recent extension of the WDF definition as a quantum quasiprobability distribution of number and phase and as a wide-band distribution function in signal processing.

UTD multiple-edge transition zone diffraction

Abstract: The uniform theory of diffraction (UTD) is applied to multiple absorbing screens, which are in the transition zones near shadow boundaries. The theory includes the application of slope diffraction, which is a first-order effect in transition zone diffraction. By choosing length parameters independently for amplitude and slope diffraction, it is ensured that the solution has continuity of amplitude and slope at each point. The solution is compared with known solutions with good results except when two screens are very near each other. The study is of particular interest to radio propagation over terrain in mobile radio systems.

Comparison of different theories for focusing through a plane interface

Abstract: We consider the problem of light focusing by a high-aperture lens through a plane interface between two media with different refractive indices. We compare two recently published diffraction theories and a new geometrical optics description. The two diffraction approaches exhibit axial distributions with little difference. The description based on geometrical optics is shown to agree well with the diffraction optics results. Also, some implications for three-dimensional imaging are discussed.

CADDRAD: a physical optics radar/radome analysis code for arbitrary 3D geometries

Abstract: CADDRAD is a radar/radome analysis code meant to aid in the design of modern radar radomes on aircraft. Arbitrary radome shapes may be input in a standard format used by computer-aided-design software. Multi-layered radomes, with thickness tapers in all layers, may be used. The radar may be either electronically or mechanically scanned. The underlying theory implemented in the code is discussed. Comparisons are shown between measurements and predictions of reflection lobes, beam peak loss, and boresight error.

Uniform asymptotic solution for electromagnetic reflection and diffraction of an arbitrary Gaussian beam by a smooth surface with an edge

Abstract: A closed form solution is obtained to describe, in a physically appealing manner, the reflection and diffraction of a general astigmatic Gaussian beam which is incident on an arbitrary smooth, electrically large, slowly varying curved, perfectly conducting screen (or reflector). This closed form solution is obtained via an asymptotic evaluation of the radiation integral for the fields scattered from the reflector, to within the physical optics approximation that remains valid for the present situation. The analysis developed here is particularly well suited for the fast analysis of electrically large reflector antennas by representing the feed illumination by a relatively small set of Gaussian beams launched from the feed plane. Each of these Gaussian beams after being launched undergoes reflection and diffraction at the reflector; the expressions for the reflected and diffracted fields are developed in this paper and utilized by Chou [1996] to compute the radiation pattern of large reflector antennas in a matter of a few seconds as compared to the conventional numerical physical optics integral method which takes hours on the same computer.

Paraxial light and atom optics: The optical Schrödinger equation and beyond

Abstract: Paraxial light and atom optics are compared. To lowest order the slowly varying amplitude of a light field in a dielectric medium with a spatially dependent refractive index satisfies an equation which has the form of a Schr\"odinger equation: the ``optical Schr\"odinger equation.'' The unsystematic procedure of neglecting certain second-order derivatives is replaced by a systematic expansion which allows the calculation of consecutive corrections. The general theory is applied to harmonic motion in a graded index fiber and to tunneling between coupled fibers. The physical relations between wave evolution of massive particles and paraxially propagating waves are elucidated.

Late-time target response measured with terahertz impulse ranging

Abstract: Time-domain impulse-scattering measurements of freely propagating single cycle terahertz radiation from dielectric targets is measured in the far field with subpicosecond resolution. Initial specular reflection as well as late-time response of the targets is observed to approximately 100 times the initial pulse width. Measured scattered fields agree well with the calculated scattering for early- and late-time response in both the time and frequency domains. The data is fit to both an inverse Fourier transform of numerically calculated frequency domain scattering as well as an intuitive model based on physical optics (PO). The PO picture is verified directly in the time domain and surface wave propagation velocities are measured.

The rotating wave approximation (RWA) of quantum optics: serious defect

Abstract: The rotating wave approximation (RWA) is an integral part of the foundations of quantum optics and it is also used extensively in atomic and condensed-matter physics. Here we prove that the model has a serious defect, viz. the spectrum has no lower bound, for all models of physical interest. As a result, the reservoir is not passive (since energy can be extracted from it without limit) and hence the second law of thermodynamics is not satisfied. An alternative to the RWA is discussed.

Antenna Engineering Using Physical Optics

Abstract: This book sets itself the rather ambitious task of providing programs in three languages. It does not limit itself to the FORTRAN language, which has traditionally been the workhorse of most scientific and engineering software-development efforts, and is routinely used by engineers. The C language and its variations, such as C++, are very popular these days. One of the strengths of this book is that it shows the feasibility of the application of the MATLAB language to antenna field problems using the physical-optics approach, which makes it also a nice and useful introduction to the physical-optics method in electromagnetics. The book uses the term physical optics loosely to denote all methods of finding radiated fields via a process of integration of approximate equivalent currents with appropriate Green's functions.

T-Matrix computations of zenith-enhanced lidar backscatter from horizontally oriented ice plates

Abstract: Zenith-enhanced backscattering (ZEB) of a lidar beam by cirrus clouds is a remarkable phenomenon usually explained in terms of specular reflection from large plane facets of horizontally oriented ice plates. Since the standard geometric optics approximation (GO) may be inapplicable in many cases, especially in analyzing infrared measurements, and ignores physical optics effects, we use the recently improved exact T-matrix method to compute the scattering of light by ice plates at visible and infrared wavelengths. Computations for horizontally and randomly oriented thin disks and oblate spheroids with size parameters up to 50 show that while all particles produce a strong Fraunhofer diffraction peak centered at exactly the forward-scattering direction, a strong and narrow ZEB peak can be produced only by horizontally oriented disks but not by horizontally oriented spheroids or particles in random orientation. This finding demonstrates that ZEB can be produced even by particles which are not in the GO domain of size parameters and supports the traditional interpretation of ZEB. Also, we have found that the angular width of the ZEB peak for horizontally oriented disks is equal to half the width of the Fraunhofer diffraction peak. This result can be used in practice to derive a lower estimate of ice particle sizes from high angular resolution measurements of ZEB. We show that our exact T-matrix computations can explain the peculiar zenith-angle dependence of depolarization observed by Platt et al. [1978] in the visible and can be interpreted qualitatively in terms of the modified Kirchhoff approximation.

An approximation of the radiation integral for distorted reflector antennas using surface-error decomposition

Abstract: The physical optics/aperture integration (PO/AI) formulation is often used to analyze the radiation patterns of reflector antennas. In this study, the PO/AI radiation integrals for distorted reflector antennas are addressed. The surface error of the antennas is approximated by a series of surface expansion functions. The radiation integral is decomposed into a series of radiation-type integrals, each of which corresponds to one of the surface expansion functions. Each of these radiation-type integrals is then weighted by amplitude coefficients. The advantage of performing the decomposition is that each of the radiation-type integrals can be computed and the pattern data stored. The computation of the pattern for a distorted reflector antenna with a changing error profile is performed by recalling the pattern data for each perturbation term and weighting it with the amplitude coefficient. This facilitates rapid evaluation of the radiation integral in cases where the error profile is changing (for example, time-varying errors). The superposition of integrals presented in this paper was shown to be valid for surface-error profiles up to 0.1 /spl lambda/ rms amplitude.

Numerical modeling of a nonuniform grating with FDTD

Abstract: The need for a numerical analysis of a nonuniform grating arises from antenna testing facilities. A hologram type of compact antenna test range (CATR) is a recently proposed method for antenna testing at millimeter wavelengths. Simulations of the quiet-zone field are done with a two-dimensional finite-difference–time domain method (FDTD), combined with an exact near-field aperture integration method [physical optics (PO)]. © 1997 John Wiley & Sons, Inc. Microwave Opt Technol Lett 15: 134–139, 1997.

Improved numerical simulation of electromagnetic wave scattering from perfectly conducting random surfaces

Abstract: A Monte Carlo simulation of electromagnetic scattering from one-dimensional perfectly conducting random surfaces is considered in the paper. Surface profiles of desired statistics are generated numerically using a standard procedure and the scattering solution for the surface samples of finite length is calculated using the method of moments. A new technique is used to reduce the effect of the edges of the finite surface samples. In this technique, the conductivities of the surface near edges are controlled by adding an appropriate tapered resistive sheet. It is shown that the accuracy at large angles of incidence, thetas > 50°, and the computation efficiency are improved significantly using this method, when compared to the standard tapered illumination method. Results based on this numerical approach are compared with those based on the small perturbation and physical optics approximations in their respective regions of validity.

Numerical analysis of the interference patterns in the optical transmission spectra of a square photonic lattice

Abstract: The interference patterns in the transmission spectra of a two-dimensional square photonic lattice calculated by the plane-wave expansion method are compared with its photonic band structure in detail. The effective refractive indices obtained by both calculations correspond to each other quite well. In addition, aperiodic and singular interference patterns are found when the incident plane wave excites two eigenmodes with mutually different wave vectors.

Optics and Vision

Abstract: List of Tables. Physical Constants. 1. Light and Vision - A Historical Perspective. 2. Production and Measurement of Light. 3. Geometrical Optics. 4. The Thick Lens. 5. Vergence and Vision. 6. Cylindrical Lenses and Astigmatism. 7. Aberration Theory. 8. Controlling Light through Optical Systems. 9. Optical Instrumentation. 10. Optics of the Eye. 11. Light as Waves. 12. Lasers and the Eye. 13. Interference Phenomena. 14. Interference Applications. 15. Polarized Light. 16. Fraunhofer Diffraction. 17. Fiber Optics. Answers to Selected Problems. Index.

Generation of nearly nondiffracting bessel beams with a fabry-perot interferometer

Abstract: A new concept for generating zero-order Bessel beams was studied theoretically. The spatial intensity distribution was calculated numerically using a wave optics model. Approximate analytical expressions were derived to describe the radial intensity distribution in planes perpendicular to the optical axis of an imaging lens.

Polarization waves as observable phenomena

Abstract: The concept of the polarization wave is introduced by bringing together under this name a series of generally space–time-varying polarization phenomena. Unlike the light wave, the polarization wave belongs to the class of observable phenomena. The mathematical entities describing the polarization waves are introduced in an inductive way starting from some fundamental examples. The issues are conceived as a further step in building the optics of observables.

Chemical Oxygen-Iodine Laser Performance Modeling

Abstract: We have developed a detailed engineering model for chemical oxygen-iodine laser (COIL) performance and design predictions. In this model, mixing between the primary oxygen and the secondary iodine injectant is treated using a two-stage/three-stream shear-layer model based on the flow characteristics of the transverse injection mixing scheme. Iodine dissociation, excited-state pumping, and quenching processes are treated using the Phillips Laboratory standard COIL kinetics package. Optical extraction from a stable resonator is described by a rooftop geometric optics model. These models have been incorporated into a two-dimensional Advanced Cavity Code for COIL (AC3). The detailed models in AC 3 have been systematically validated by comparing detailed code results reflecting a hierarchy of computational complexity with data from relevant experiments. The validity of the mixing, kinetics, and optics models has been corroborated by comparing the predictions of the code with iodine dissociation, laser small signal gain, and optical power measured in the RotoRADICL device. Selected small signal gain and output power measurements from the low pressure RotoCOIL were also reproduced by the model. Computational results showed good agreement with power measurements from the high efficiency RotoRADICL/JogRADICL experiments with different throat heights. Also, predicted results showed reasonably good agreement with the dissociation and power data obtained using the RADICL device and the baseline or Big-volume generator. Output power data obtained with Rocketdyne's closed-loop Mini-GDU device were excellently predicted by the model. The good agreement with the data obtained from various devices encompassing a broad range of experimental parameters lends credibility to this model. Without an elaborate CFD and wave optics model, the good agreement strongly suggests that the present model contains the essential physics for adequate modeling and prediction of COIL performance.

Electromagnetic backscattering from aircraft propeller blades

Abstract: This paper gives a theoretical solution to the problem of determining the electromagnetic backscattering and Doppler spectrum of an aircraft propeller as presented to a radar operating in the 8-12 GHz band. At this band for all practical aircraft propeller the electromagnetic backscattering regime is in the optical region. The solution proceeds by modeling the aircraft propeller as a set of multiple skew-plated metal fan blades in the presence of a linearly polarized EM wave. Based on the quasi-stationary method combined with physical optics and physical theory of diffraction equivalent currents techniques are used to analyse the backscattering from aircraft propeller blades. Experimental results indicated that, in the far zone, the field can be considered as harmonic and expressions for the spectral components of the field are obtained. The observed waveforms are found to be in good agreement with theoretical results.

G/T maximization of a paraboloidal reflector fed by a dipole-disk antenna with ring by using the multiple-reflection approach and the moment method

Abstract: A 1.8-m paraboloidal reflector fed by a dipole-disk antenna with a beamforming ring is optimized for high G/T at L-band by using the moment method (MM) and the multiple reflection (MR) approach. The MR approach is based on using MM to calculate the radiation and scattering patterns of the feed, using physical optics plus uniform geometrical theory of diffraction (UTD) to include the reflector, and in addition to include the mutual interaction (multiple reflections) between the reflector and the feed by using the expression for the sum of an infinite geometric series. The MR approach is shown to be equally accurate as a MM solution of the complete antenna with reflector, provided the reflector is in the far field of the feed, and the MR approach is much faster. As a result of the calculations using the MR approach, design curves are presented showing how the G/T varies as a function of antenna geometry, size, and elevation angle, all for a given noise profile of the surrounding sky and ground. The computed radiation patterns and G/Ts are compared with measurements for several elevation angles and surrounding terrain.

Near-field scattering by physical theory of diffraction and shooting and bouncing rays

Abstract: The problem of electromagnetic wave scattering is very important in defense applications. The research on this topic was mostly centered on far-field analysis: assume an incident plane wave, compute its scattered field due to the scatterer, and evaluate the radar cross section (RCS) of the scatterer. When the transmitting and receiving antennas are far from the scatterer, the incident wave can be approximated by a plane wave on every part of the target, the far-field analysis thus applies. However, in practical applications, there are many situations that the distance between the transmitting antenna and the scatterer is not large enough to treat the field arriving the scatterer as a plane wave. In these conditions the far-field analysis is not valid, and a near-field analysis is necessary. Most scattering papers on academic journals are related to the far-field analysis. The only near-field study that the author knows is the NcPTD code developed in DEMACO by Lee (1991). However, in this study only the physical theory of diffraction (PTD) is modified to deal with near-field scattering of convex scatterers. The method of shooting and bouncing rays (SBR), which is useful in evaluating the far-field RCS of concave targets, was not included. Also, the formulae are not explicit. This paper presents the PTD and SBR formulae for near-field scattering from a unified view.

Optical collection efficiency function in single-molecule detection experiments

Abstract: The optical collection efficiency function for an optical system such as that used in single-molecule detection experiments is studied. Closed analytical expressions based on a geometrical optics approximation are presented. Comparison is made with exact wave optics calculations.

Beam diameter effects on microwave reflectometer measurements

Abstract: Simulation results of the reflectometer phase and power sensitivity from a two-dimensional physical optics model show that a tightly focused reflectometer beam is most appropriate for fluctuation measurements, while a larger beam diameter appears more appropriate for density profile measurements.

Equivalence between physical optics and aperture integration for radiation from open-ended waveguides

Abstract: The eigen-mode radiation from an open-ended waveguide of arbitrary cross section is considered. The following theorem is demonstrated: the Kirchhoff-Kottler aperture integration for the radiated field is equivalent to the physical-optics (PO) approach applied to the wall currents. This theorem allows one to resort to aperture integration for those structures involving complicated PO integration. On the other hand, based on the same theorem the aperture integration may be reduced to a line integral along the edge of the waveguide for those configurations that allow a simple PO integration. It can also be useful in developing more efficient solutions in the framework of incremental theories.

Scattering of Electromagnetic Plane Waves by Conducting Plates

Abstract: We studied the scattering of electromagnetic plane waves by an arbitrarily shaped conducting plate using the physical theory of diffraction (PTD). When the integrand contains only the linear phase term, the radiation integral of physical optics (PO) transforms into a contour integral along the periphery of the plate. Its asymptotic solution for a convex plate is derived by applying t he stationary phase method of integration when the dimension of the plate is large in comparison to the wavelength. We applied this expression to the special cases of circular and elliptic plates, and the results agreed with the asymptotic solutions derived from the exact. PO solutions (Airy patterns). Taking into account, the relation between the Airy patterns and their asymptotic solutions for circular and elliptic plates, we derived a caustic corrected expression for an arbitrary convex plate. An asymptotic expression of the non-uniform edge correction for the convex plate was derived by applying the equivalent cu...

Iterative solutions of MFIE for computing electromagnetic scattering of large open-ended cavities

Abstract: The analysis of high-frequency scattering from electrically large open cavities is addressed in the paper. A magnetic-field integral equation (MFIE) for the equivalent currents on the interior cavity walls is obtained and solved by two different algorithms based on high-frequency principles of physical optics (PO). Once the currents are known, the scattered fields are obtained by using aperture integration (AI) in the cavity mouth, or a reciprocity integral (RI) over a surface close to the termination. Numerical results are presented which demonstrate the convergence and accuracy of the proposed methods, by comparison with modal reference solution.

Exact solution for a penetrable wedge structure

Abstract: A structure consisting of four penetrable wedges with a common edge is considered. For a certain polarization and direction of incidence of the primary plane wave, the edge does not scatter and geometrical optics is the exact solution. Two derivative structures are described that also do not scatter-one consisting of two parallel edges and the other of the junction of two parallel-plate waveguides.

Renormalization Group in Mathematical Physics and Some Problems of Laser Optics

Abstract: An original approach to constructing special type symmetries for boundary value problems, RENORMGROUP SYMMETRIES, is reviewed here. It is applied to a system of geometric optics equations. New solutions to the laser beam self-focusing problem are presented.