Showing papers on "Physical optics published in 1979"

Critical angle scattering by a bubble: physical-optics approximation and observations

Abstract: The intensity of light scattered by an air bubble in water is predicted by the geometric-optics calculation of Davis (1955) to have a divergent angular derivative as the critical scattering angle ϕc is approached. Effects of diffraction in the angular region near ϕc are described here. The Fraunhofer diffraction for scattering angles ϕ≤ϕc is estimated using a simplified physical-optics approximation. A ringing and decay of the far-field intensity is predicted that is formally similar to the near-field diffraction of a straight edge. Observation of millimeter radius bubbles in water with collimated monochromatic illumination confirm the existence of this ringing which has a quasi period ≃ 25 mrad. The diffraction calculation gives an approximate description of the relative ϕ of the observed maxima and minima. Fringes with a lower contrast and spacing ≃ 0.3 mrad were also observed; they appear to be caused by the interference of rays with distinct paths. Implications for the critical angle scattering of white light are discussed.

Diffraction from discrete and homogeneously structured ionospheric irregularities

Abstract: Diffraction patterns produced by isolated irregularities have a maximum fading depth at radio frequencies near 0.6 ƒT where ƒT, the transition frequency, is a property of the electron density irregularity and marks the boundary between geometric and physical optics. A nearly homogeneous assembly of irregularities can produce scintillation which is speciously random. For such an assembly a peak in scintillation depth is also produced just below the mean fT. At radio frequencies below the scintillation is fast and frequency independent; above ƒ¯T the amplitude pattern is directly related to the ionospheric structure.

Geometric optical theory of diffraction gratings

Abstract: The aberration theory of diffraction gratings has been studied by means of geometric optics. No restrictions are imposed on the form of the grating surface, the pattern of the grooves in the grating surface, and the position of the object. Furthermore, the image plane is not limited to one normal to the principal ray. All of the terms up to the fourth order with respect to the pupil coordinates are taken into account in a series expansion of the light path function. The results give the focal positions, the radius of curvature of the astigmatic image, the shape of this image, the optimum slant angles of the image plane, the resolution by geometric optics, and the condition for absence of comatic broadening.

Exact expressions for scalar modal eigenvalues and group delays in power-law optical fibers

Abstract: Considerable use is made of power-law refractive-index profiles in fiber optics. These profiles have simple scaling properties that are exploited in this paper to obtain formulas for the exact modal propagation constants and group delays. When an infinite profile is assumed, the results of the exact, WKB, and geometric optics theories are all shown to agree. This conclusion remains valid when linear material dispersion is included. The effect of the cladding is discussed. The results are correct for noncircular fibers of power-law type.

A three-dimensional vectorial theory for volume holograms

Abstract: The wave conversion process in a volume phase hologram, recorded by two monochromatic waves satisfying geometrical optics, is studied. Coupled wave differential equations are derived and. from the solutions given in a companion paper, numerical results are presented for plane-to-plane, plane-to-spherical, and spherical-to-plane wave conversion. It is shown that in the non-paraxial case the polarization of the input wave may significantly change during transit through the hologram.

Quasi-homogeneous sources and geometrical optics

Abstract: It is shown that the quasi-homogeneous model of a partially coherent source predicts the same optical-intensity distribution across the Fresnel and Fraunhofer regions as would be predicted by geometrical optics.

An extension of geometrical optics to polarized light

Abstract: Following closely the Kline-Kay derivation of Lunebourg's method, the author shows that for isotropic media the spinor formalism of the optics field supplies a new mathematical formulation of classical geometrical optics with in addition polarization and transport equations for the electric and magnetic fields. This new theory, not so complete as the Kline-Kay theory is much easier to handle and could be of interest in some optical systems where polarization variations are important.

Geometrical optics field of general optical systems

Abstract: Using the stationary phase approximation of the Kirchoff diffraction integral, we derive a general expression for the field in the image space of a point source for an arbitrary optical system. The concept of an “optical path matrix” (OPM), which is the Hessian of the point eiconal, is introduced. Luminosity, caustic surfaces, and evanescent fields are defined in terms of the OPM. Detailed consideration of the single-interface problem yields solutions in terms of the Gaussian, mean, and normal curvatures of the interface. A complete solution of the simple lens is given as an example of a system with two refracting surfaces.

Two-dimensional nonimaging concentrators with refracting optics

Abstract: We show how to design a concentrator with refracting optics having the maximum theoretical concentration ratio chromatic aberration is neglected and skew rays are ignored.

Experimental aspects of transition phenomena in quantum optics

Abstract: Phase transitions in equilibrium systems are the result of a competition between the interparticle energy J and the thermal energy kBT which introduces disorder. In quantum optics, even when interparticle interactions are negligible as in a very dilute gas, there may be particle correlations due to the common radiation field. The transition from disorder to order consists in a passage from a regime where the atoms emit independently from one another, to a regime where the atoms emit in a strongly correlated way. It depends on a “cooperation number” C which is proportional to the atomic density. In a “pumped” system, as the density of active atoms is increased, the laser threshold is reached for C=1 and the coherent e.m. intensity is proportional to C-1.

Phase-Conjugate Optics,

Abstract: A new research area in coherent optics has emerged and has been receiving increasing attention from many scientists as its important applications are recognized. Phase conjugate optics is the name which seems to have attached itself to this new field. The main feature of phase conjugate optics is the generation of an electromagnetic wave with a phase distribution which is, at each point in space, the reversal of that of an arbitrary incoming monochromatic wave. The wavefront, after being generated, proceeds to propagate in the opposite direction, retracing in reverse the path of the incoming wave. Thus, the phase reversal or conjugation process results in what is frequently called a time-reversed replica of the incident wave. If we consider, as an example, an incoming spherical wavefront which, diverging from a point, has a radius of curvature R, its conjugate-replica will be an outgoing spherical wavefront converging toward the same point and with a radius of curvature -R. Phase conjugation techniques have been used in the past for imaging through phase distorting media; well known examples can be found in holography [1] and adaptive optical systems [2]. The new and attractive feature, which differentiates phase conjugate optics from the previous techniques, is the use of nonlinear optical mixing to generate in real time without the need for intermediate electronics, and with amplification if desired, a time-reversed replica of an incident wave.

Receiving and transmitting properties of small grid paraboloid by moment method

Abstract: The receiving and transmitting properties of a grid paraboloidal reflector of aperture diameter 273λ and f/D ratio 0395, operating at 410 MHz, are analysed using the moment method For the receiving situation, with a normally-incident plane wave illuminating the reflector, the distributions of current, obtained in the inner grids only, show a close resemblance to those predicted by the physical optics approximation It is shown that neither maximum scattered nor maximum total electric field on axis is received at the geometrical focus, but at a point between this focus and the vertex This result is in agreement with that calculated by the physical optics method for small solid paraboloids of the same f/D ratio Contours of scattered off-axis fields are also presented in the geometric and true focal planes of the paraboloid as well as in longitudinal planes of such a reflector In the transmitting situation, the grid paraboloid is excited by a centrally driven couplet feed, positioned at different points along the axis It is shown that the feed position affects considerably the distributions of current in the feed elements but not in the reflector grids, and confirms that defocusing the couplet feed results in an increased forward power gain

Foundation of geometrical optics in general relativistic dispersive media

Abstract: Geometrical optics in dispersive media is rigorously derived from Maxwell’s equations by employing the two‐timing method An effect analogous to Faraday rotation is found for the polarization plane of the wave, with the vorticity of the medium taking the place of the magnetic field

Simplified Predictive Methodology For Nonlinear Repetitive Pulse And CW High Energy Laser Propagation

Abstract: Systems analysis studies frequently require simplified predictive methodology for determining nonlinear thermal blooming effects on a high energy laser beam propagating through the atmosphere. Because of the many variables, tens of thousands of propagation runs may be required in the course of a systems study. As a result, the wave optics codes are generally not practical due to excessive computation times. A methodology highly suitable for systems analysis has been constructed by observing that a phase integral can be defined which has the properties of a similarity variable. For a particular aperture plane beam shape, a high energy laser beam propagating through a convective medium experiences beam spread due to thermal blooming which can accurately be correlated as a simple function of the phase integral. A few well chosen wave optics calculations provide the data base for the correlation which then becomes a "scaling law". This scaling law expresses the dependence of the non-linear beam spread as a function of beam properties such as power, pulse repetition frequency, wavelength, Fresnel number and atmospheric properties such as absorption, transmission and wind speed. This correlation is combined with formulations for jitter and turbulence providing the basis for a simple yet highly accurate predictive methodology.© (1979) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Directional spectra of ocean waves from microwave backscatter: A physical optics solution with application to the short-pulse and two-frequency measurement techniques

Abstract: Two simple microwave radar techniques that are potentially capable of providing routine satellite measurements of the directional spectrum of ocean waves were developed. One technique, the short pulse technique, makes use of very short pulses to resolve ocean surface wave contrast features in the range direction; the other technique, the two frequency correlation technique makes use of coherency in the transmitted waveform to detect the large ocean wave contrast modulation as a beat or mixing frequency in the power backscattered at two closely separated microwave frequencies. A frequency domain analysis of the short pulse and two frequency systems shows that the two measurement systems are essentially duals; they each operate on the generalized (three frequency) fourth-order statistical moment of the surface transfer function in different, but symmetrical ways, and they both measure the same directional contrast modulation spectrum. A three dimensional physical optics solution for the fourth-order moment was obtained for backscatter in the near vertical, specular regime, assuming Gaussian surface statistics.

High-intensification regions of gravitational lenses.

Abstract: We examine the intensification, I, near the singular points in the object plane of an extended spherical gravitational lens. Geometrical optics predicts an infinite I for a point object located on a singularity. The function I, however, turns out to be integrable over the object plane. We make a detailed physical optics calculation for I. No singularities appear, and there are some interesting, marginally detectable diffraction phenomena. The two types of bright regions, the ''halo'' and the ''spike,'' behave very differently. Simple order-of-magnitude expressions give estimates for the brightness and duration of a high-intensification event.

Institute of Optics 1929-1979: a brief commemorative.

Abstract: On the occasion of the fiftieth anniversary of the founding of the Institute of Optics of the University of Rochester, its history, staff, and students, and its interactions with and influence in the world of optics are briefly reviewed. The author, wife of one of the two original faculty and herself an opticist, observes from the sidelines.

Conservation laws for geometrical optics in general-relativistic refractive media

Abstract: The area-intensity law of geometrical optics is derived from Maxwell’s equations in general-relativistic refractive media.

Rough surface scattering of horizontally polarized waves and polarization dependence of backscatter cross section: Full wave solutions

Abstract: Full wave solutions are presented for horizontally polarized waves scattered by rough surfaces. Complete expansions and exact boundary conditions are used in the analysis. These solutions are compared with the physical optics solution based on the local tangent approximation of the fields at the irregular boundary. Expressions for the backscatter cross section for both horizontally and vertically polarized waves are also compared with earlier solutions to this problem. The reciprocity relationship and the suitability of the approximate impedance boundary condition are examined, and special consideration is given to excitation and scattering at grazing angles. This work on irregular ground effects on radio wave propagation can be applied to problems of communication, navigation, positioning, and active remote sensing.