Showing papers on "Physical optics published in 1990"

Contemporary College Physics

Abstract: Measurement and analysis motion in one dimension motion in two dimensions force and motion uniform circular motion and gravitation work and energy linear momentum combining conservation of energy and momentum rigid bodies and rotational motion fluids thermal physics gas laws and kinetic theory thermodynamics periodic motion wave motion electric charge and electric field electric potential and capacitance electric current and resistance magnetism electromagnetic induction alternating-current circuits geometrical optics optical instruments wave optics relativity the discovery of atomic structure origins of the quantum theory quantum mechanics the nucleus lasers, holography, and colour condensed matter elementary particle physics.

Spectral properties of light in quantum optics.

Abstract: The problem of spectral filtering of quantized light fields is studied, based on the recently developed quantum-optical theory of the action of passive, lossless optical systems [L. Kn\"oll, W. Vogel, and D.-G. Welsch, Phys. Rev. A 36, 3803 (1987)]. Expressions for the operator of the electric field strength of the light and the normally and time-ordered field-correlation functions are derived for the case of a Fabry-P\'erot interferometer being present. Various kinds of field decomposition that are usually considered in classical optics are studied. The results are compared with the Fourier approach to spectral properties of light. It is shown that, dependent on the experimental scheme used, new quantum effects appear, which may prevent the observation of the Fourier structure of the light as predicted from classical optics. Quantitatively this is demonstrated for the example of spectral squeezing in resonance fluorescence, where significant discrepancies between the measured and the full Fourier spectrum are found.

Wave-optics description of laboratory soft-x-ray lasers

Abstract: We describe a time-dependent wave-optics propagation model applicable to laboratory x-ray lasers and amplified spontaneous emission devices described in the literature. The model embodies a stochastic treatment of spontaneous emission, counterpropagating beams, diffraction, gain saturation, transverse variation of gain, and refractive effects due to electron density gradients. The model has been used to describe the output beam characteristics and spatial coherence properties of some plausible lasers.

Millimeter wave scattering model for a leaf

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.

A numerical study of the separation wavenumber in the two-scale scattering approximation (ocean surface radar backscatter)

Abstract: The modeling of radar backscatter from the ocean uses the two-scale scattering approximation. This approximation assumes that the continuous spectrum of the ocean can be separated at some wavenumber into large- and small-scale surfaces, allowing use of physical optics and small perturbation methods. The authors investigate the choice of the separation wavenumber by comparing two-scale calculations and exact numerical calculations for a randomly rough surface with a power law spectrum. >

A UTD type analysis of the plane wave scattering by a fully illuminated perfectly conducting cone

Abstract: A uniform high-frequency asymptotic solution, based on the physical optics (PO) approximation, is obtained in the format of the uniform geometrical theory of diffraction (UTD) to describe the fields diffracted by the tip of a semi-infinite, perfectly conducting cone when it is fully illuminated by an electromagnetic plane wave. The solution is expressed in terms of an integral, over finite limits which can be integrated numerically without difficulty. The results computed from the uniform asymptotic PO solution compare well with previously published results given for narrow-angle semi-infinite cones. In addition, they compare well with measurement and with an independent moment method (MM) solution for the scattering by a finite flat-backed cone in which several higher order wave interactions are found to be significant; one such interaction is between the tip and the base of the cone. Expressions are provided which are useful for calculating this tip-base interaction and confirm its relative importance. These expressions also provide tip diffraction effects which are important within the forward paraxial zone for the radiation by antennas on cones. >

Polarization correction and extension of the Kennaugh-Cosgriff target-ramp response equation to the bistatic case and applications to electromagnetic inverse scattering

Abstract: An analytical time-domain expression derived by Kennaugh (1967) for the early time impulse response for smooth, convex, perfectly conducting scatterers under the physical optics approximation for the bistatic case is reinterpreted. The physical optics bistatic early time impulse responses can be interpreted as cross-sectional areas of the scatterer. A crude polarization correction to the leading edge of the physical optics impulse response is obtained for the bistatic case, leading to a simple asymptotic relation between the specular principal curvature difference and certain co-polarized phase terms in the bistatic scattering matrix. Applications to direct scattering are discussed. Profile reconstruction from bistatic data with a priori knowledge of the validity range of physical optics in the time domain is proposed and tested with the sphere. >

Matching optics for gaussian beams

Abstract: A system of matching optics for gaussian beams. The matching optics system is positioned between a light beam emitter (such as a laser) and the input optics of a second optics system whereby the output from the light beam emitter is converted into an optimum input for the succeeding parts of the second optical system. The matching optics arrangement includes the combination of a light beam emitter, such as a laser with a movable afocal lens pair (telescope) and a single movable lens placed in the laser's output beam. The single movable lens serves as an input to the telescope. If desired, a second lens, which may be fixed, is positioned in the beam before the adjustable lens to serve as an input processor to the movable lens. The system provides the ability to choose waist diameter and position independently and achieve the desired values with two simple adjustments not requiring iteration.

Near‐nadir radar backscatter from a well‐developed sea

Abstract: The Kirchhoff approximation for the case of well-developed seas is analyzed. In this peculiar case, the equilibrium range in the wave number spectrum corresponds to a cascade pattern in the surface geometry. Its high wave number cutoff is shown to be a major factor of the radar backscatter. This intrinsic scale is evaluated, and both the geometrical and the physical optics terms are related to major parameters of wind-wave dynamics. The range of validity of the Kirchhoff approximation and the relative importance of the diffraction correction are analyzed. Finally, the radar cross section sigma exp 0 of well-developed seas is compared with that of poorly developed seas. The great qualitative difference shown in the wind speed dependence of sigma exp 0 for these two regimes is pointed out as a source of a considerable error trend recently discovered in satellite altimeter wind measurements.

Adaptive optics system performance approximations for atmospheric turbulence correction

Abstract: Analysis of adaptive optics system behavior often can be reduced to a few approximations and scaling laws. For atmospheric turbulence correction, the deformable mirror (DM) fitting error is most often used to determine a priori the interactuator spacing and the total number of correction zones required. This paper examines the mirror fitting error in terms of its most commonly used exponential form. The explicit constant in the error term is dependent on deformable mirror influence function shape and actuator geometry. The method of least squares fitting of discrete influence functions to the turbulent wavefront is compared to the linear spatial filtering approximation of system performance. The author finds that the spatial filtering method overestimates the correctability of the adaptive optics system by a small amount. By evaluating fitting error for a number of DM configurations, actuator geometries, and influence functions, fitting error constants verify some earlier investigations. Limitations of the approximations and scaling laws are evaluated and compared to wave optics ground-to-space propagations. Results include determination of a multiplicative conversion factor of 1.06 that should be applied to the actuator spacing whenever the spatial filtering method is used for adaptive optics system performance analysis.

Analysis of blended rolled edge reflectors using numerical UTD

Abstract: The uniform geometrical theory of diffraction (UTD) concept is used to predict the scattered fields in the target zones of compact-range reflectors. Since the necessary diffraction coefficients are not known in a closed form, a numerical method to calculate the diffraction coefficients is described. In the numerical method, the problem is reduced to two dimensions, and physical optics line integration is used to compute the diffraction coefficients. Thus, the method is computationally efficient. The method is used to analyze two compact-range reflectors. The results obtained using the numerical UTD show good agreement with the scattered fields obtained using a corrected physical optics surface integration. >

The slightly-rough facet model in radar imaging of the ocean surface

Abstract: The slightly-rough facet model of the ocean surface, an extension of the two-scale radar scattering model, is well suited for investigating synthetic aperture radar (SAR) imaging of the surface. We derive several statistical properties of the facets that are important in an imaging model. The two-scale scattering model is extended to include both first-order and second-order large-scale effects (tilt and curvature) using physical optics, showing that a spectrum of small-scale ripples, rather than a single ripple given by the Bragg resonance condition, contributes to the backscatter from a facet. The bandwidth of the resonant ripple spectrum depends on the radar wavelength, large-scale curvature and illumination widths. The properties of the facets are deduced from this dependence. The large-scale curvature of the surface determines the size of the facets. The expected facet size depends directly on the radar wavelength and is much smaller than the resolution of realistic radars. The resonant ripp...

Real-time radar cross section of complex targets by physical optics graphical processing

Abstract: It is shown that the radar cross section (RCS) of complex targets can be obtained in real time using the hardware capabilities of a high-performance graphics workstation. Target geometry is modeled by a computer-aided-design package. The RCS is computed using the physical-optics high-frequency approximation. In order to validate the graphic processing of the surface integral, the results obtained for simple objects are compared with analytic evaluation of the physical-optics integral. A generic missile model is used to validate the physical-optics results for complex radar targets at high frequency. It is found that the RCS of complex targets at high frequency is predicted with reasonable accuracy by the physical-optics approximation. >

Time-domain physical-optics analysis of large reflector antennas

Abstract: The time-domain analysis of large reflector antennas is presented. Physical-optics time-domain analysis is used to determine the antenna characteristics under pulse-modulated RF excitation. The resulting far fields for a front-fed paraboloid are shown. The waveforms of the incident wave and scattered field are plotted. From these patterns one can determine buildup and decay transient time as a function of reflector diameter or observer look angle. Using the peak of the steady-state field for different look angles, one can determine the gain pattern of the reflector, which agrees exactly with the gain pattern obtained directly from frequency-domain analysis. >

Nonlinear optics and dynamics in passive semiconductors

Abstract: In this paper we review nonlinear optical effects in semiconductors under high excitation. After a short description of the incorporation of nonlinear effects into Maxwell’s equations we give some selected examples of their experimental evidence. This includes bulk semiconductors as well as quasi-two and-zero dimensional systems. Thermally induced nonlinearities are used to introduce basic concepts of nonlinear dynamics and synergetics. Here we show the appearance of temporal as well as of spatial structures in semiconductors.

A very accurate model for backscattering by right angled dihedral corners

Abstract: An accurate model for backscattering by a perfectly conducting 90 degrees dihedral corner is presented. This model has been obtained by adding to the IPO (improved physical optics) model the PTD (physical theory of diffraction) contribution, and makes it possible to accurately predict the monostatic radar cross section of the corner in a plane normal to its wedge. Representative results are 5.67 in the case of normal polarization. >

A concise conjugate gradient computation of plate problems with many excitations

Abstract: One of the major difficulties in the application of the conjugate gradient algorithm for the analysis of electromagnetic scattering problems is the necessity to carry out the calculation separately for each incident wave. In the approach suggested, rather than handling the incident waves directly, a class of possible excitations is represented by a set of strip-type basis functions. For these functions, convergence is predictable and rapid because the majority of the strips are located away from the edges of the scatterer. This choice also facilitates the use of the physical optics approximation as a good initial guess. Once the solutions for all the unit basis functions over the body are known, they can be combined to synthesize the solution for any excitation using the weighting coefficients associated with the expansion of the incident field. Numerical examples are given, and they demonstrate the substantial savings achieved by adopting this approach for the analysis of multiple excitations. >

Linear-phase approximation in the triangular facet near-field physical optics computer program

Abstract: Analyses of reflector antenna surfaces use a computer program based on a discrete approximation of the radiation integral. The calculation replaces the actual surface with a triangular facet representation; the physical optics current is assumed to be constant over each facet. Described here is a method of calculation using linear-phase approximation of the surface currents of parabolas, ellipses, and shaped subreflectors and compares results with a previous program that used a constant-phase approximation of the triangular facets. The results show that the linear-phase approximation is a significant improvement over the constant-phase approximation, and enables computation of 100 to 1,000 lambda reflectors within a reasonable time on a Cray computer.

Study of the Phase Perturbation Technique for Scattering of Waves by Rough Surfaces at Intermediate and Large Values of the Roughness Parameter

Abstract: The phase perturbation technique is numerically examined in the case of scalar waves scattered by one-dimensional normally distributed random rough surfaces, on which Dirichlet boundary conditions hold. Particular attention is devoted to surfaces for which the Rayleigh parameter has intermediate or large values. It is shown that the considered method is not limited to either small roughness or gentle undulations. It is demonstrated that the phase perturbation technique smoothly interpolates between the two classical approximations, namely the perturbation approach and the Kirchhoff method. The cases in which the phase perturbation theory converges to physical optics are characterized by large values of the Lynch parameter. A conclusion is drawn that the phase perturbation technique is amenable to surfaces whose roughness spectra are wide. Asymptotic expansions, simplifying the evaluation of the phase perturbation backscattering cross-section in the high roughness limit are derived.

Channel optical waveguides in polyimides for optical interconnection by laser-direct writing and contact printing

Abstract: The feasibility of constructing graded-index (GRIN) Polymer Microstructure Waveguides (PMSWs) on various substrate surfaces, including semiconductors, conductors, insulators, and ceramics, has been consistently proven. The PMSW formed by Physical Optics Corporation (POC) is at least one to two orders of magnitude larger than those constructed by the state-of-the-art microstructure formation systems such as MOCVD and MBE. The polymer material used possess a large dynamic range of temperature stability (from -180°C to +200°C) and wide transmission bandwidth (from 0.3 pm to 2.7 im wavelengths). Local sensitization technique applied to PMSW has also been introduced to facilitate the formation ofplanar multiplexed holographic gratings for single wavelength 1-to-many fanouts and wavelength division (de)multiplexing (WD(D)M). Realization of such technology is useful for optical interconnection, signal processing and communication.

Iterative radar target imaging based on modified extended physical optics method

Abstract: The modified extended physical optics method, which assumes the physical optics current property over the entire surface of conducting scatterers, is applied to the inverse problem of target profile imaging. The usefulness of the modified extended physical optics method for the direct backscattering problem is first demonstrated. Then this method is applied to the inverse problem, by introducing the phase factor determined iteratively for the shadowed portion of the target and by performing the Fourier transformation of the backscattered field in the frequency domain. As an example, the inverse profiling of nose-on spheroids, including a sphere, is tested and discussed. >

Near axial backscattering from finite cones

Abstract: The near-axial backscattering from a finite cone is studied using the equivalent current concept based on the uniform geometrical theory of diffraction (UTD). The creeping waves associated with the conical surface are also incorporated into the equivalent current technique. The contributions from the creeping waves are significant for the oblique-incidence case. There is evidence to speculate that the poorer agreement between the previously calculated results and the measured data for the vertically polarized backscattering is probably a result of the omission of the creeping wave contribution. >

Four-telescope phased array optical simulation

Abstract: A new geometric and physical optics simulation code for predicting the performance of phased array telescopes is described. A skew aspheric ray trace routine computes a composite spot diagram and an array of optical path differences for the entire telescope system. This includes the four nearly identical afocal telescopes and the single combiner telescope. A second routine then computes subaperture Zernike aberration coefficients. A wave optics code computes point spread functions, and a final code computes optical transfer functions. The simulated performance of Air Force's Multipurpose Multiple Telescope Testbed (MMTT) is then presented and discussed. All optical surfaces of the telescope plus in situ measured aberrations are simulated. The results show that the telescope is nearly diffraction limited at small field angles, but suffers from phase and tilt differences among the telescopes at field angles above two milliradians.

Crosspolar control in far-field synthesis of dual offset reflectors

Abstract: The possibility of synthesising dual offset reflector systems to produce a prescribed far-field power pattern with no depolarisation is examined under the principles of geometrical optics. A formulation is developed based upon a model in which both source and antenna far fields are represented by Huygen's fields. Numerical implementation in general appears difficult but a useful special case emerges in which the reference axes of the Huygen's fields are parallel. Results for a contoured beam application reveal that a shaped dual offset system with no optical depolarisation is possible, and further analysis using physical optics suggests that extremely good axial ratios can be obtained.

Holographic rugate structures for x-ray optics applications

Abstract: Physical Optics Corporation (POC) has proposed and investigated a novel approach to x-ray optics during this DOE-sponsored three-year program, based on our well-established technologies in volume holography and holographic materials. With these technologies, a majority of conventional XUV optical elements, such as uniform and nonuniform gratings/multilayers, lenses, slanted (non-Snellian) mirrors, Fresnel zone-plates, concentrators/collimators, beam splitters, Fabry-Perot etalons, and binary optical elements, can be fabricated using a unified, low cost process. Furthermore, volume holography offer nonconventional optical elements, such as x-ray holographic optical elements (HOEs) with any desirable wavefront formation characteristics and multiple gratings multiplexed in the same volume to perform different operations for different wavelengths, that are difficult or even impossible to produce with the existing technologies.