Showing papers on "Physical optics published in 1967"

Polarization analysis of natural and artificially induced geomagnetic micropulsations

Abstract: The polarization characteristics of geomagnetic micropulsations are investigated using quasi-monochromatic wave train theory of physical optics. The polarization of a wave train is analyzed by considering the coherency matrix of the wave field. The elements of the matrix are calculated over the desired frequency band and the polarization parameters evaluated. Since the determinant of the coherency matrix is zero for a totally polarized wave field, this property can be used to separate a partially polarized wave field into its polarized and unpolarized parts. The ellipticity, orientation, and sense of polarization for the polarized portion are then calculated in terms of the matrix elements using power and cross-power spectral analysis techniques. Based on this approach, the polarization of a number of different signals has been digitally determined. Test cases include a random number time series, a constructed signal with a predetermined polarization, and an example typical of geomagnetic micropulsations resulting from high-altitude nuclear weapons tests superimposed on high natural background. The results of these analyses are then compared with those from the standard hodogram technique and the effectiveness of both methods discussed in terms of the signal characteristics.

Wave‐Optical Aspects of Lorentz Microscopy

Abstract: The customary defocused and Foucault modes of Lorentz microscopy of magnetic films are usually described in terms of geometric optics. However, Wohlleben has shown that geometric optics has a restricted range of validity; a more fundamental approach is provided by wave optics. The defocused and Foucault modes may be discussed in terms of wave optics, and for the defocused mode, it can be shown explicitly that the geometric theory is simply the first approximation to the wave‐optics theory. Consideration of wave optics also leads to the proposal of two additional modes of Lorentz microscopy: Zernike phase‐contrast and interference microscopy; these modes cannot be described on the basis of geometric optics. The most fundamental problems in magnetic films which are amenable to study by Lorentz microscopy are investigations of the fine structures of domain walls and magnetization ripple. These problems are discussed in terms of wave optics for all four modes of Lorentz microscopy; in particular, the intensit...

Propagation in random media--Cumulative effect of weak inhomogeneities

Abstract: The effect of weak, random inhomogeneities on wave propagation is studied. Of particular concern is the case of long distance propagation where the nature of the wave is significanfly affected by the inhomogeneities. Conventional perturbation techniques such as geometrical optics and the Born and Rytov approximations cannot be applied in this realm. The approximation technique employed is basically a selective summation technique of the type utilized in other areas of physics such as quantum electrodynamics and the theory of many-body interactions. Results are obtained for the average value and two-point correlation function of an arbitrary, initial wave. A physical interpretation of the results in terms of coherent and incoherent scattering and the classical theory of dielectrics is given. Wave statistics and the application of the results to the problem of determining the effect of the atmosphere on coherent optical communication are discussed.

Systematic Approach to the Teaching of Lens Theory

Abstract: A general description of optical instruments is presented, which can be used to treat geometrical optics, Fourier optics, and the wave theory in a unified manner. It is shown that a joint treatment of these various branches of optics clarifies many results that quite often remain intuitively obscure to the student; e.g., the Legendre transformations in eikonal theory attain an immediate significance in the context of the wave theory. Students of a course along these lines must have a moderate knowledge of Fourier integrals. In the final section it is shown that diffraction theory can be described in terms of a “sum over all rays” concept.

Omnidirectional scattering of acoustic waves by rough, imperfectly reflecting surfaces.

Abstract: The omnidirectional scattering of acoustic waves by a rough, imperfectly reflecting surface is described using the method of physical optics. The expression for the far‐zone intensity is derived and then specialized to the case of surfaces that are sufficiently rough to neglect the specularly reflected power. For such surfaces, the average differential scattering cross section σ0 is calculated and compared with the results of bistatic measurements made under conditions that satisfy the assumptions of the theory.

Traveling Waves in Relation to the Surface Fields on a Semi-Infinite Cone

Abstract: For a plane electromagnetic wave at nose-on incidence on a semi-infinite perfectly conducting cone expressions for the surface field components are obtained. These have been programmed for numerical computation and data are presented for the magnitudes and phases as functions of the distance from the tip for three different cone angles. Comparison with results derived from the physical optics approximation and from a simple wedge approximation shows that the differences between the exact and physical optics values are not attributable to a tip-excited wave.

Application of geometrical optics to the design and analysis of microwave antennas

Abstract: : The basic concepts of geometrical optics together with the additional assumption that lead to the 'geometrical optics approximation' are described here. The eikonal equation is derived and the relationship of exact electromagnetic theory in the limit as wavelength approaches limit of 0 to geometrical optics is made evident. The application of the 'geometrical optics approximation' to phase analysis and synthesis is described and an example of synthesis is presented. The concept of power flow in ray tubes is used to obtain approximations to power distributions in the antenna aperture, in the focal region, and in the far field. Ray analysis is used to determine those feed locations in the focal region that will most nearly collimate the far-field rays that lie in certain desirable planes. The Theorem of Malus is used to formulate the equal path length law and applications are given. Focal surfaces (or caustics) relative to a rectilinear congruence are defined and then used to present a geometrical optics description of the focal region. The equations of the focal surfaces of a paraboloid receiving a plane wave 20 degrees off-axis are calculated and photographs of three-dimensional models of the focal surfaces are shown.

Memorandum on analysis of echo area of targets using geometrical theory of difraction and creeping wave theory - 2430-1

Abstract: : A combination of creeping-wave analysis and diffraction theory has been developed for determining the radar cross section of bodies for which exact solutions are not available. The known solutions for the perfectly conducting cylinder and sphere have been used to specify attenuation and diffraction coefficients for the creeping wave. The creeping wave contribution is added to the geometrical optics or physical optics contribution from the specular point to determine the total scattered field. It is demonstrated that this type of solution is applicable to ogives, ogives with spherical caps, and prolate spheroids. Wedge diffraction theory has been combined with creeping wave analysis to calculate the edge-on backscatter of circular and ogival disks. It is necessary to modify the magnitudes, but not the forms, of the creeping wave attenuation and diffraction coefficients when treating a creeping wave on an edge. This form of analysis is adaptable to calculation of the radar cross section of composite bodies where both volumetric shapes and edges may occur in combination. Once the specular points, wedge diffraction points, and the attachment points and paths of the creeping waves are determined the computation of the scattered field is straightforward.

Research laboratory of electronics quarterly progress report no. 86, july 15, 1967,

Abstract: : Contents: Molecular beams; Molecular energy transfer and spectroscopy; Microwave spectroscopy; Atomic resonance and scattering; Radio astronomy; Optical and infrared spectroscopy; Geophysical research; Magnetic resonance; Physical electronics and surface physics; Physical acoustics; Electrodynamics of media; Physical optics of invertebrate eyes; Plasma physics; Gaseous electronics; Plasmas and controlled nuclear fusion; Energy conversion research; Spontaneous radiofrequency emission from hot-electron plasmas; Interaction of laser radiation with plasmas and nonadiabatic motion of particles in magnetic fields; Statistical communication theory; Processing and transmission of information; Detection and estimation theory; Speech communication; Linguistics; Cognitive information processing; Communications biophysics; Neurophysiology; Computation research.

Erratum: Generalized Physical Optics Approximation for the Scattering of Electromagnetic Radiation from Imperfect Conductors of Irregular Shape

Abstract: The scattering of electromagnetic waves from plasmas of arbitrary shape (underdense and absorptive, overdense and/or collision‐dominated) is calculated in the physical optics limit (wavelength short compared to a radius of curvature of the surface of the body). For infinitely conducting plasmas, the results for perfect conductors are recovered, and it is shown that the radar cross section for plasmas with a finite conductivity is, in general, polarization dependent, in contrast to the case of a perfect conductor.