Showing papers on "Physical optics published in 1971"

Method of Edge Waves in the Physical Theory of Diffraction

Abstract: : The diffraction of plane electromagnetic waves by ideally conducting bodies, the surface of which have discontinuities, is investigated in the report. The linear dimensions of the bodies are assumed to be large in comparison with the wavelength. The method developed takes into account the perturbation of the field in the vicinity of the surface discontinuity and allows one to substantially refine the approximations of geometric and physical optics. Expressions are found for the fringing field in the distant zone. A numerical calculation is performed of the scattering characteristics, and a comparison is made with the results of rigorous theory and with experiments.

Mode Coupling in First-Order Optics

Abstract: A simple procedure is described to obtain the modes of propagation in square-law lens-like media. This procedure consists of evaluating the geometrical-optics field created by a point source at the input plane of an optical system (called mode-generating system) with nonuniform losses. An expansion of the field in power series of the coordinates of the point source gives the modes of propagation. In the case of optical resonators, the mode-generating system is described by the modal matrix of the resonator round-trip ray matrix. This representation of modes by point sources allows the coupling factor between two modes with different parameters (beam radii, wave-front curvatures, and axes) to be evaluated without integration. Only matrix algebra is used. In the general three-dimensional case, the coupling factor is expressed as a product of Gauss functions and Hermite polynomials in four complex variables. The quantities introduced are generalized ray invariants.

Electromagnetic wave propagation in a radially and axially non-uniform medium: optics of SELFOC fibres and rods; wave optics considerations

Abstract: This communication presents an analysis of the propagation of an electromagnetic wave in a medium in which the variation of dielectric constant is of the form = (0) - (2)(Z)r2. Explicit expressions for the intensity at any point have been obtained for (2)(Z) = constant, and numerical calculations have been presented for the case when (2)(Z) = 20(1+αZ)−2 and compared with the results obtained earlier, using the geometrical optics approximation. These two forms for the variation of (2)(Z) with Z correspond to the cylindrical and conical SELFOC fibres and rods.

Electromagnetic inverse scattering

Abstract: An Electromagnetic Inverse Scattering Identity, based on the Physical Optics Approximation, is developed for the monostatic scattered far field cross section of perfect conductors. Uniqueness of this inverse identity is proven. This identity requires complete scattering information for all frequencies and aspect angles. An integral equation is developed for the arbitrary case of incomplete frequency and/or aspect angle scattering information. A general closed form solution to this integral equation is developed, which yields the shape of the scatterer from such incomplete information. A specific practical radar solution is presented. The resolution of this solution is developed; yielding short-pulse target resolution radar system parameter equations. Special cases, such as a priori knowledge of scatterer symmetry, are treated in some detail. The merits of this solution over the conventional radar imaging technique are discussed.

Modes in General Gaussian Optical Systems Using Quantum-Mechanics Formalism

Abstract: A new method is developed for mode calculation in optical systems by use of quantum-mechanics formalism. Scalar approximation of optical waves is used. It is shown that in gaussian optics a very simple rule applies, which gives modes when ray propagation is known by the geometrical method. These modes are shown to be Weber–Hermite functions. Applications are considered in general optical resonators.

Reflection and Scattering from a Time‐Varying Rough Surface—the Nearly Complete Lloyd's Mirror Effect

Abstract: The effect of a rough, moving surface upon transmission between an omnidirectional source and receiver in an isovelocity medium is described using the method of physical optics. This is done by relating the spectral density of the source and the wave spectrum of the surface and also the geometry. The dependence of the received spectrum upon the interference between the direct and reradiated waves and the characteristics of the “frequency smearing” caused by scattering are described. A favorable comparison of the theory with the results of an experiment performed under near‐ideal conditions in a model tank is made. [Work supported by the U. S. Navy Electronic Systems Command.]

Geometric optics in an ideal magnetohydrodynamic fluid.

Abstract: The propagation of small monochromatic disturbances in a stable ideal magnetohydrodynamic fluid is treated by the method of geometric optics. The medium is trirefringent and requires six systems of rays. The problem of a point radiator is solved in the small wave-length limit where the theory holds.

Radiative Properties of Rough Surfaces

Abstract: Most studies on surface roughness effects are based on geometrical optics. This analytical investigation treats the surface roughness effects from wave optics considerations, thus accounting for the interference of waves. The rough surface is sinusoidal, infinite in extent and it is irradiated by plane monochromatic waves. The scattering of electromagnetic waves by the rough surface is determined by the direct solution of Maxwell's equations instead of the commonly used Huygens-Kirchhoff approximation (Beckmann's reflectance). Consequently, the solution is not restricted to small wavelength to roughness ratios; furthermore, polarization effects can be accounted for. The results indicate that the transmittance of the rough surface exhibits a maximum near the point where the wavelength of the surface roughness is the same as the wavelength of the radiation. The interval around this point is called transition region because the surface changes from specular to diffuse. The radiative properties are influenced by both the pitch and amplitude of the roughness. The results approach Fresnel's law when the pitch and amplitude of the surface become small compared to the wavelength of the radiation. Similarly, the surfaces become specular even at larger pitch if the amplitude of the roughness is small. It is also shown that Beckmann's reflectance relation is the limiting case of the reflectance obtained by the direct solution of Maxwell's equations. In addition, numerical results are presented on the effective properties of rough dielectric plates with various refractive indices and optical thicknesses.

Analysis of Acoustic Wave Scattering by a Composite Rough Surface

Abstract: The effect of surface irregularities upon the scattering performance of a composite rough surface that consists of scattering elements of structure sizes in quite different scale uniformly superimposed one on the other is described and analyzed. The theory is formulated on the basis of the principles of both geometrical optics and physical optics through the introduction of the surface‐slope distribution with a result clear in physical meaning and simple for analysis. Three factors determine the dominating role played by the component irregularities in wave scattering: surface slope, incident angle, and wavelength. An example showing the angular distribution of wave scattering by a composite rough surface at frequencies of 1 and 100 kHz about 7 oct apart is presented. At low frequency, the backscattering is confined to a narrow region of about 10° centered at the direction of normal incidence, while at high frequency, the angular distribution expands to about 150°. As for the bistatic scattering the angular distribution of the scattered acoustic wave increases from about 25° centered at specular reflection to 180°. This effect of the small‐scale surface irregularities is to broaden the angular distribution of the scattered acoustic wave at high frequency.

Formalism of Geometrical Optics for Flexure Waves

Abstract: The equations of geometrical optics governing the ray shape and the energy transport along the rays are obtained for flexure waves propagating on an inhomogeneous finite weight plate. Krasil'nikov's results for the energy flux vector and the amplitude relations along the rays are generalized both in the absence and in the presence of liquid loading.

Quantitative Microscopic Holography

Abstract: Since the audience for this discussion is at least partially comprised of life scientists, it may be appropriate to begin by mentioning some facts of microscopy and physical optics with which they may not be completely familiar. These facts impose constraints under which any endeavors in magnifying and imaging, whether holographic or otherwise, must labor.© (1971) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Research on Imaging Properties of Optical Parametric Upconverter

Abstract: : The imaging properties of parametric upconversion have been investigated analytically and experimentally for the case of monochromatic object waves, and photographs of upconverted 10.6 micrometers images obtained. Using geometric optics an expression was derived relating the locations of the object, the pump and the upconverted image. The effect of higher order factors such as crystal birefringence, phase mismatch, and pump wave divergence were considered qualitatively. The analysis was then extended by applying the techniques of physical optics. Using Fourier transformer formalism an expression was derived relating the angular spectrum of the sum-frequency field with that of the object and pump fields. Two cases were examined in detail, one using a plane wave pump and the other with a Gaussian distributed pump beam.

The Short-Backfire Antenna: A Numerical-Physical Optics Study of Its Characteristics,

Abstract: : A numerical-physical optics method is applied to study the circuit (impedance) and radiation characteristics of the short-backfire antenna. This radiator, developed through extensive experimentation by AFCRL, consists of a dipole exciter located between a large rimmed reflector and a small secondary reflector. It has wide bandwidth and high directivity comparable to sophisticated reflector antennas. In the numerical-physical optics method, the following steps are followed: (1) a set of coupled integral equations for the currents excited in the dipole and on the surface of the secondary reflector are formulated and solved numerically, assuming for this step that the large reflector is infinite; (2) the surface currents of the large reflector are approximated by a truncated form of those calculated for the infinite conducting sheet; (3) the radiation field maintained by the currents of the steps (1) and (2) is calculated; and (4) a diffracted field correction is made to account for the finite dimensions of the large reflector and its rim. This method has the advantage, relative to earlier studies, that it can successfully predict the antenna's circuit characteristics. Excellent results are obtained for both square and circular geometries. Comparison is made with experimental measurements made by AFCRL. (Author)

Coherent Optics -- A Tutorial Review

Abstract: There may be some doubt as to what the title Coherent Optics refers to. To me it means that part of optics that depends upon the coherence of the light for its description. Classically, of course, long before the word partially coherent light came into use, coherent systems were known and formed the basis for that portion of the study of light called Physical Optics. Hence interfer-ence and diffraction phenomena are well recognized; interferometry has developed into a discipline all its own with a wide ariety of types of interferometers that confound the neophyte. Many of the various interferometers are named which provides a listing that looks like a scientific "who's - who" --Michelson, Mach-Zehnder, Twyman-Green, Fizeau, Fabry-Perot, Rayleigh, Lummer-Gehrcke, Jamin, Sirks-Pringsheim ........, interferometers. Again we must pity (with a certain amount of smug superiority) the uninitiated who doesn't realize the difference between Fabry-Perot fringes and Fizeau fringes. The literature contains many works on interferometry, the intent reader may well refer to Steel (1967), Tolansky (1955), Candler (1951).