Showing papers on "Physical optics published in 1994"

Comparison of numerical models for computing underwater light fields

Abstract: Seven models for computing underwater radiances and irradiances by numerical solution of the radiative transfer equation are compared. The models are applied to the solution of several problems drawn from optical oceanography. The problems include highly absorbing and highly scattering waters, scattering by molecules and by particulates, stratified water, atmospheric effects, surface-wave effects, bottom effects, and Raman scattering. The models provide consistent output, with errors (resulting from Monte Carlo statistical fluctuations) in computed irradiances that are seldom larger, and are usually smaller, than the experimental errors made in measuring irradiances when using current oceanographic instrumentation. Computed radiances display somewhat larger errors.

Geometrical Theory of Diffraction

Abstract: Details the ideas underlying geometrical theory of diffraction (GTD) along with its relationships with other EM theories.

Time-domain physical-optics

Abstract: The authors extend the concept of the frequency-domain physical-optics approximation to the time domain, and use it to determine some significant properties of large reflector antennas. When this method is used to determine the equivalent surface-current density on the reflector, the effects of time-delayed mutual coupling between points on the surface are ignored. Consequently, many of the numerical limitations found in other conventional time-domain techniques are avoided, e.g. boundary-truncation error, interpolation error, numerical dispersion error, numerical instability, error accumulation with time marching, etc. More significantly, this method requires relatively small amounts of computer memory and CPU time. Several applications to the transient analysis of pulsed radar systems are given. >

Transverse nonlinear optics: Introduction and review

Abstract: The characteristics features of the field of Transverse Nonlinear Optics are briefly illustrated, as an introduction to this special issue of Chaos, Solitons & Fractals .

Spatial coherence of a Gaussian-beam wave in weak and strong optical turbulence

Abstract: A generalized Huygens–Fresnel integral, valid for optical wave propagation through random inhomogeneities in the presence of any complex optical system characterized by an ABCD ray matrix, is used to derive a general expression for the mutual coherence function (MCF) associated with a Gaussian-beam wave in the weak-fluctuation regime. The mean irradiance obtained from this expression shows excellent agreement with all known asymptotic relations. By introducing a pair of effective beam parameters Θt and Λt that account for additional diffraction on the receiving aperture, resulting from turbulence, the normalized MCF and the related degree of coherence are formally extended into the regime of strong fluctuations. Results for the normalized MCF from this heuristic approach compare well with numerical calculations obtained directly from the formal solution of the parabolic equation. Also, the implied spatial coherence length from this analysis in moderate-to-strong-fluctuation regimes generally agrees more closely with numerical solutions of the parabolic equation than do previous approximate solutions. All calculations are based on the modified von Karman spectrum for direct comparison with established results.

High frequency approximations to the physical optics scattering integral

Abstract: Discusses two high frequency (HF) approximations to the physical optics (PO) scattering integral for the far field radar backscatter from a general curved edged reflecting surface viewed at arbitary aspect. The PO scattering integral is first approximated as the sum of a specular effect and an edge effect, where the latter is represented explicitly as a certain line integral evaluated over the boundary edge of the reflector. A closed form result is then obtained by applying the method of stationary phase to the line integral. With the exception of singularities that can occur at caustics, or when the specular point falls on the boundary edge, these HF approximations are found to work reasonably well for smooth surfaces whose Gaussian curvatures have constant sign (positive or negative, but never zero). >

A design procedure for classical offset dual reflector antennas with circular apertures

Abstract: A geometrical optics procedure for designing electrically optimized classical offset dual reflector antennas with circular apertures is presented. Equations are derived that allow the size and spacing of the main and subreflectors of the antenna system, along with the feed horn subintended angle, to be used as input variables of the design procedure. The procedure, together with these equations, yields an optimized design, starting from general system requirements. The procedure is demonstrated by designing both an offset Cassegrain and an offset Gregorian antenna, and is validated by analyzing their radiation patterns using physical optics surface current integration on both the main and subreflectors. >

Current trends in optics

Abstract: Atomic optics, S.M. Tan and D.R. Walls single atoms in cavities and traps, H. Walther meet a squeezed state and interfere in phase space, D. Krahmer et al can light be localized?, A. Lagendijk time-resolved laser induced breakdown spectroscopy, G. Lupkovics et al fractal optics, J. Uozumi and T. Asakura on the spatial parametric characterization of general light beams, R. Martinez-Herrero and P.M. Mejias to the unseen - vision in scattering media, E.P. Zege and I.L. Katsov backscattering through turbulence, A.S. Gurvich and A.N. Bogatorov why is the Fresnel transform so little known?, F. Gori Fourier curios, A.W. Lohmann the future of optical correlators, D. Casasent spectral hole burning and optical information processing, K.K. Rebane holographic storage re-visited, G.T. Sincerbox colour information in optical pattern recognition, M-J. Yzuel and J. Campos the optics of confocal microscopy, C.J.R. Sheppard diffraction unlimited optics, A. Lewis super-resolution in microscopy, V.P. Tychinsky and C.H.F. Velzel fringe analysis - anything new?, M. Kujawinska diagnosing the aberrations of the Hubble Space Telescope, J.R. Fienup laser beacon adaptive optics - boon or bust?, R.Q. Fugate

Generalization of the Maxwell-Bloch equations to the case of strong atom-field coupling

Abstract: We derive the generalized set of Maxwell-Bloch equations which takes into account the dependence of relaxation coefficients on the amplitude and frequency of the coherent field. This has interesting implications in many problems in quantum optics and laser physics, e.g., the problem of lasing without inversion due to a strong coherent generating field.

Full wave solutions for rough-surface bistatic radar cross sections: Comparison with small perturbation, physical optics, numerical, and experimental results

Abstract: In this paper, full wave solutions are derived for the like- and cross-polarized electromagnetic fields diffusely scattered by two-dimensional rough surfaces. These expressions for the diffuse scattered fields are used to obtain the random rough-surface cross sections. The rough surface is characterized by a Gaussian joint probability density function for the surface heights and slopes at two points. These full wave results are compared with the associated small-perturbation results and physical optics results. They are also compared with experimental and numerical results (based on Monte Carlo simulations). The earlier assumption that the surface height and slopes can be considered to be uncorrelated is examined. The impact of using the large-radii curvature assumption and including self-shadow is also considered.

Optical realization of the baker's transformation

Abstract: The quantization of a completely chaotic system-the baker's transformation-is investigated using the fact that the relationship between classical and quantum mechanics is directly analogous to the one between ray and wave optics. A class of optical systems is constructed for which the ray dynamics is governed by the baker map. Applying wave-optical methods to these physical systems then gives, in the standard way, their corresponding quantum dynamics. The result is that in certain cases the quantum propagator is identical to that found previously using an ad hoc mathematical quantization procedure. However, this is not always so-for other systems with the same classical (ray) limit there are important differences. In particular, the propagator need not be block-diagonal in its q-p' representation, as had previously been assumed, although it always tends to this basic form in the semiclassical limit.

Edge effects of truncated periodic surfaces of thin wire elements

Abstract: The effects of truncating a periodic structure of thin wire elements is examined. The structure is assumed to be infinite in extent along a single axis, enabling the analysis to be simplified via Floquet's currents on the infinite axis for plane wave incidence. The analysis of an infinite linear array of elements is thereby reduced to that of a single element. Scattered fields are presented for several truncated planar geometries and are compared to three approximate solutions that use unperturbed two-dimensionally infinite Floquet currents, diffraction from a strip, and a physical optics solution for a strip, respectively. >

Diffractive optics applied to free-space optical interconnects

Abstract: The optimum design of free-space optical interconnection systems utilizing diffractive optics is determined from a practical engineering standpoint for systems ranging from space invariant to fully space variant. System volume is calculated in terms of parameters such as the f-number of the diffractive lens, the wavelength of light, and also the total number, size, and separation of the optical sources and detectors. Performance issues such as interconnection complexity, diffraction efficiency, and signal-to-noise ratio are discussed. Diffractive optics fabricated by electron-beam direct-write techniques are used to provide experimental results for both shuffle-exchange and twin-butterfly free-space optical interconnects.

From wave theory to ray optics

Abstract: The aim of this article is to summarize the historical process which led to recovering the concept of a ray, typical of the pre-Maxwell theory of light, from wave theory. To this end, the contributions of Huygens (1690), Newton (1704), Young (1801), and Fresnel (1816), which can be considered the founders of the modern science of optics, are briefly described, giving evidence to some aspects that led to the formulation of the ondulatory theory of light. Then, it is seen how the concept of a ray was recovered from Kirchhoff's diffraction theory, which can be interpreted as a rigorous formulation of Fresnel's ideas. The key role of the Maggi-Rubinowicz (1888, 1924) representation of Kirchhoff's diffraction integral, which can be interpreted as the mathematical expression of Young's theory of diffraction, is discussed. Also, it is noted that the first theoretical derivation of diffracted rays, and of the cone of diffraction, was due to Adalbert Rubinowicz (1917). He was one of Sommerfeld's assistants, in Munich, in analyzing the transmission of a high-frequency field through an aperture in an opaque screen. The ideas which are briefly summarized produced the basis for the statement of the geometrical theory of diffraction. This ray theory, which is the natural extension of geometrical optics (GO), was presented by J.B. Keller, in 1953. >

Adaptive optics for astronomy

Abstract: Preface. Part I: The Problematics of Adaptive Optics. Introduction to Wave Optics C.A. Haniff. Atmospheric Turbulence Optical Effects: Understanding the Adaptive Optics Implications D.L. Fried. Atmospheric Adaptive Optics Applications V.P. Lukin. Modelling Atmospheric Turbulence Effects on Ground-Based Telescope Systems L.W. Bradford, S.M. Flatte, C.E. Max. Servo-Loop Analysis for Adaptive Optics M. Demerle, P.Y. Madec, G. Rousset. The Problematics of Adaptive Optics Design F. Roddier. Part II: Critical Components and Systems. Wavefront Sensing G. Rousset. Optimization of Wavefront Sensors for the Highest Accuracy and Sensitivity J.R.P. Angel. Deformable Mirrors E.N. Ribak. Astronomical Reference Sources F. Rigaut. Sodium-Layer Laser Guide Stars H.W. Friedman. Synthetic Beacons for Atmospheric Compensation D.P. Greenwood, R.R. Parenti. Sodium Beacon Used for Adaptive Optics on the Multiple Mirror Telescope B.J. Carter, et al. Evaluating the Performance of Adaptive Optical Telescopes B.M. Welsh, M.C. Roggemann. Integrated Adaptive Optics Systems E.H. Richardson. Stray Radiation Issues in Astronomical Systems with Adaptive Optics S.M. Pompea. Active Compensation of Global Wavefront Tilts E. Ballesteros, T. Viera, F. Lorenzo, M. Reyes, J.A. Bonet, C. Martin. Part III: Astrophysics with Adaptive Optics. The Impact of Adaptive Optics on Focal Plane Instrumentation S.T. Ridgway. Prospects for Alternative Approaches to Adaptive Optics A.H. Greenaway. Adaptive Optics for Long Baseline Optical Interferometry J.-M. Mariotti. Astrophysics with Adaptive Optics: Results and Challenges P. Lena.Index.

A Unified Theory of Multidimensional Electromagnetic Vector Inverse Scattering Within the Kirchhoff or Born Approximation

Abstract: Multidimensional inverse scattering has very important applications in radar, medical diagnostics, geophysical exploration and nondestructive testing. As such, acoustic, electromagnetic and elastic waves are involved. The mathematics of wave propagation, scattering and inverse scattering differs considerably in complexity for these various types of waves. Acoustic waves can be considered as strictly scalar, whereas electromagnetic waves require field vectors, and field quantities to describe elastic waves are vectors as well as tensors. In terms of Green’s functions: a scalar Green function is sufficient for acoustic waves, a dyadic one is most appropriate for electromagnetic waves, and for elastic wave propagation, a dyadic and a triadic Green function is needed. Green’s functions determine the scattering of waves, the “inverse” of Green’s functions determines inverse scattering of waves; therefore, acoustic inverse scattering has found the earliest solutions (compare [4.1, 2] for a summary, as far as multidimensional linearized inverse scattering is considered). On the other hand, the utilization of polarization information for electromagnetic imaging has been considerably stimulated in two subsequent workshops [4.3, 4]. This can be achieved finding polarization-dependent target descriptors and signatures, or, more quantitatively, solving the electromagnetic vector inverse scattering problem. Starting from some ideas developed for the scalar case, a number of authors [4.5–9] have already tried to extend them to the vector case. Here, we want to evaluate a unified theory of multidimensional acoustic inverse scattering [4.1, 2] for electromagnetic waves; our underlying model of the direct scattering process is linear and relies on the weak scattering (Born) approximation for the penetrable scatterer, and the physical optics (Kirchhoff) approximation for the perfect scatterer. It is essentially based on the definition of the generalized holographic field, the derivation of the Porter-Bojarski integral equation, and its solution in terms of a multifrequency (transient) or multi-look-angle experiment; we call those experimental modes of operation frequency diversity, and angular diversity. The theory can be formulated in a coordinate-free version for arbitrarily located and arbitrarily shaped measurement surfaces, or in a diffraction tomographic version using Cartesian coordinates; then, the measurement surface is considered to be planar. Various data processing schemes can be established, for instance, multidimensional Fourier inversion and observation space backpropagation techniques; in the frequency diversity mode, time domain backpropagation schemes are available. The algorithms can either be derived for multistatic or monostatic arrangements; for the latter case, frequency diversity is mandatory.

Vector Beam Propagation Method for Guided-Wave Optics

Abstract: Modeling and simulation are essential to the development of integrated optical guided- wave devices. In principle, the problems can be described precisely by Maxwell equations with given boundary conditions and constitutive relations that are connected with other physical aspects. These equations may be solved by various existing techniques in electromagnetics and other branches of physics. In practice, however, the extremely high ratio of device length and optical wavelength makes many well-established methods in other areas such as microwaves not feasible or effective. Despite constant effort in adapting and applying various sophisticated analytical and numerical methods to guided-wave optics in the past two decades, the most popular approaches in the field are still the effective index method (EIM) W, the coupled-mode theory (CMT) [2], and the beam propagation method (BPM)[3].

Geometric phase with photon statistics and squeezed light for the dispersive fiber.

Abstract: The nonadiabatic geometric phase for an arbitrary cyclic evolution of the state vector for a system described by the quantum theory of the propagation of a single-mode off-resonant field through the dispersive fiber is discussed here. The sensitivity of the geometric phase on the initial field statistics has been explicitly shown in the calculations. We also derive the expressions of the geometric phase when the system is prepared initially in a squeezed coherent state.

A novel wide-angle low-loss dielectric slab waveguide Y-branch

Abstract: A new Y-branch structure for dielectric waveguides is proposed and analysed using simple geometrical optics and beam propagation methods. It is shown both qualitatively and quantitatively that the proposed structure has larger branching angles but lower radiation loss than those associated with either conventional Y-branches or structures with antenna coupled and phase front accelerators. The optimal design parameters calculated by numerical simulations are in very good agreement with those found from the geometrical optics. The simulations also reveal that the performance is fairly insensitive to fabrication errors. >

Nonlinear modulations of solitary waves

Abstract: The leading optical approximation to a slowly varying solitary crest on constant depth is the plane soliton solution with the local values of amplitude and orientation substituted. This leads to two nonlinear hyperbolic equations for the local amplitude and inclination of the crest that have been reported by several authors and predict the formation of progressive wave jumps, or shocks, from any initial perturbation of the crest. In comparison to numerical solutions of the Boussinesq equations we find that this optical approximation fails to reproduce essential properties of the crest dynamics, in particular that the crest modulations are damped and that well-defined wave jumps do not necessarily evolve. One purpose of the present work is to include such features in an amended optical approximation.We obtain the leading correction to the ‘local soliton’ solution by a multiple scale technique. In addition to a modification to the wave profile the perturbation expansion also yields a diffracted wave system and a celerity that depends on the curvature of the crest. The principle of energy conservation then leads us to a second-order optical approximation consisting of transport equations of mixed hyperbolic/parabolic nature. Under additional assumptions the transport equations can be reduced to the well-known Burgers equation.Numerical simulations of the Boussinesq equations are performed for modulations on otherwise straight crests and radially converging solitons. The improved optical, or ray, theory reproduces all essential features and agrees closely with the numerical solution in both cases. Contrary to purely hyperbolic optical descriptions the present theory also predicts wave jumps of finite width that are consistent with the triad solution of Miles (1977).The present work indicates that while sinusoidal waves often are appropriately described by the lowest-order physical optics, higher-order corrections must be expected to be important for single crested waves.

Effect of a finite ground plane on radiated emissions from a circular loop antenna

Abstract: A thin-wire circular loop antenna located above a perfectly conducting square plate is analyzed by a physical optics (PO) method. The electric field integral equation (EFIE) is solved using the method of moments to compute the current on the loop in the presence of an infinite ground plane whereby the edge effects of the plate on the loop current are neglected. The current distribution on the loop is obtained from a full-wave Fourier series analysis which requires no matrix inversion. We then use physical optics to compute the current induced on the plate in terms of the incident magnetic-field intensity. Our aim is to compare the PO solution with results obtained from a mixed wire-patch MOM code and explore its accuracy as a function of plate size and loop height. The benefits are considerable reduction in analytical and computational efforts and much less CPU time. >

Nonlinear integrated optics

Abstract: Based on the discussion of general principles and fundamental phenomena in nonlinear guided-wave optics, this article presents a review of second-order and third-order nonlinear optical waveguide devices including second harmonic generation, nonlinear directional coupler, nonlinear grating reflector, nonlinear M-Z interferomenter, etc.; the analysis and comparison of nonlinear waveguide materials and measurement techniques; and an review of the research fields and prospects of nonlinear integrated optics.

Two slit interference-classical and quantum pictures

Abstract: Young's double-slit experiment demonstrates clearly the propagation of light in the form of a wave motion. Common attempts at a quantized picture of the experiment tend to describe light in terms of the propagation of small spatially localized particles. This is wrong, and unnecessary if quantization of the electric and magnetic field vectors is considered properly. Interference between normal modes of the field is a straightforward result in both classical and quantized pictures. Such an approach sheds more light on the quantization process and on topics of interest in modern optics.

The notion of coherence in optics and its application to acoustics

Abstract: Wave phenomena are mathematically described in similar terms, even though they are of different nature, as is the case for light and sound. Yet, the basic parameters such as velocity and frequency are so different that some of the concepts defined in optics are no longer relevant in acoustics, in particular the notion of spatial and temporal coherence. We briefly present the historical evolution that led to a clear definition of coherence in optics, then we show that it is not adequate for pulse-echo ultrasound and we propose an alternative definition. This leads us to a modified and extended version of an essential theorem in the optical theory of coherence: the Van Cittert-Zernike theorem.

Dual offset shaped reflectors optimized for gain and XPD performance

Abstract: Contoured beam antennas may conveniently be designed by shaping the reflector surface to produce a gain pattern which closely resembles the prescribed coverage area. The most appropriate technique is based on using physical optics (PO) to calculate the far-field pattern and optimize, using a minimax scheme, the surface shape until the desired performance is obtained. For most contoured beams the gain performance is of primary importance, and so it usually suffices to employ single-reflector systems which are fairly simple and thus attractive from a manufacturing and implementation point of view. However, if the antenna system is to operate in linear polarization with a stringent requirement on the polarization purity, it may be necessary to adopt polarization sensitive gridding of the reflector, or use a dual reflector configuration in which the cross polarization may be reduced by appropriately tilting the main- and sub reflector with respect to the feed. This paper presents the design of a dual offset reflector antenna for a typical European coverage divided into three regions with different gain requirements and a cross polar discrimination (XPD) constraint of 33 dB. The shaping is described in some detail and a comparison is made between designs optimized with and without XPD constraints. >

Multiple cutoff wave numbers of the ablative Rayleigh-Taylor instability.

Abstract: The cutoff wave number of the incompressible ablative Rayleigh-Taylor instability is calculated using the physical optics approximation of the Wentzel-Kramers-Brillouin theory. It is found that a single value of the wave number [ital k] can correspond to multiple modes with different eigenfunctions and growth rates [gamma]. In the [gamma]-[ital k] plane the unstable spectrum is characterized by multiple branches with different cutoff wave numbers, and eigenfunctions with different number of zeros. The theory provides a formula for the cutoff wave number, valid in the regimes of interest for inertial confinement fusion capsules.