Showing papers on "Circular polarization published in 1969"

Scarabaeid beetle exocuticle as an optical analogue of cholesteric liquid crystals

Abstract: Summary 1. A review is given of the optical and architectural analogies between cholesteric liquid crystals and certain insect cuticles (Coleoptera: Scarabaeidae). Earlier observations on the optical properties (reflexion of circularly polarized light and high form optical rotation) are confirmed and extended. Both cholesteric liquid crystals and lamellate cuticle have helicoidal structure (Fig. i). Even though their chemistry and physical states are very different, we are justified in making the analogy, since their optical properties depend primarily on the pitch of their helicoidal architecture. 2. The unusual optical properties were located for the first time in the outer 5 to 20 μ of the exocuticle. This layer is transparent and has regular spacings in the range required for interference colours according to Bragg's law. Among Scarabaeid beetles which show interference colours, we distinguish two types of outer exocuticle. (i) Optically active cuticles which reflect circularly polarized interference colours; show high angles of form optical rotation in transmitted light; and anomalous form birefringence perpendicular to the cuticle surface (reversible by deproteinization). (2) Optically inactive cuticles which show none of the above properties and in which the form birefringence is parallel to the cuticle surface. In the electron microscope the ultrastructure of these two types of outer exocuticle is clearly different. 3. All of the optically active species reflect left hand circularly polarized light, irrespective of the wavelength of the reflected colour. They therefore appear dark when viewed through a right hand circular analyser. The sense of reflected circularly polarized light does not reverse at higher wavelengths as recorded by previous workers. (A simple treatment is given for combinations of various wavelengths with retardation plates of varying values, as used in circular analysers.) We confirm earlier reports that the sense of reflected circularly polarized light is of the opposite sense to the transmitted light. 4. Using monochromatic light we have measured the anomalous dispersion with wavelength of the magnitude of optical rotation for various optically active cuticles. The dispersion curves change from negative values at lower wavelengths to positive values at higher wavelengths, and cross the zero optical rotation axis at a wavelength (AQ) corresponding to the interference colour of each sample. There is reasonable agreement between A0 and the interference colour calculated from ultrastructural evidence and by comparison with interference filters of known wavelength. A dispersion curve measured for a combined sample of two cuticles with different dispersion curves showed that the resultant is an algebraic summation of the two component curves. 5. We present the first experimental verification of existing mathematical treatments of anomalous form optical rotatory dispersion curves. Although these treatments were derived for cholesteric liquid crystals, they give a reasonable fit to our measured curves for cuticle. We have confirmed from our cuticle dispersion curves that a second zero value for optical rotation occurs at a wavelength higher than A0, as predicted by the theory of Chandrasekhar and Rao (1968). This has not yet been observed in any cholesteric liquid crystal system. 6. Our evidence shows that in optically active cuticle, interference colour is determined by helicoid pitch. In Lomaptera interference coloration follows the bilateral symmetry of the insect. Hence helicoidal pitch is controlled in a bilaterally symmetrical manner. However, the sense of helicoid rotation is the same all over the beetle and is therefore bilaterally asymmetrical. This supports the view that helicoid pitch is under the local control of the epidermal cells which secrete the cuticle, whereas its sense of rotation may be determined by an extracellular self-assembly process. In view of the self-assembling properties of cholesteric liquid crystals, it is tempting to suggest that helicoidal cuticle could be formed by the stabilization of a liquid crystal. 7. We discuss in detail the differences between optically active and inactive cuticles. The constructive interference colours arising from both types are then briefly compared with other multiple layer reflecting systems in other animals. 8. A detailed comparison is made between the optics of cuticle and cholesteric liquid crystals. The optical analogy provides a two-way contact between cuticle biophysicists and liquid crystal physical chemists.

Polarization Dependence of Stimulated Rayleigh-Wing Scattering and the Optical-Frequency Kerr Effect

Abstract: A theoretical study of the polarization dependence of stimulated Rayleigh-wing scattering and the optical-frequency Kerr effect has been undertaken. When the incident light is circularly polarized, a striking difference in gain is found for the co- and counter-rotating senses of polarization of the scattered light---the former being suppressed and the latter being exceptionally favored. The analysis begins with a model for the Kerr effect, which involves the alignment of anisotropic molecules in an electric field, but the results can be immediately generalized to any light scattering process of tensor symmetry. The nonlinear problem of the propagation of an intense elliptically polarized light wave in a Kerr-active medium is shown to have a solution in which the vibrational ellipse undergoes self-precession and self-retardation. The stimulated scatterings or instabilities of such a self-precessing and self-retarding light wave are obtained for the backward and forward directions. Birefringence, optical activity, and linear and circular dichroisms are some of the phenomena which result, but the forward direction yields substantially different results from the backward direction because of Stokes-anti-Stokes coupling.

Polarization Effect in Photoionization of Cesium

Abstract: Polarized cesium atoms were ionized by circularly polarized light. The cesium-ion intensities obtained with positive and negative photon helicities were measured at various wavelengths. The results demonstrate that the wave functions for the continuum states of cesium are perturbed by a spin-orbit interaction in accordance with the theoretical interpretations given by Seaton and Fano.

The spectrum and polarization of a source of synchrotron emission with components flying apart at relativistic velocities

Abstract: In the present paper we consider the frequency spectrum, time variations and polarization of the flux of synchrotron radio emission from a source which consists of two components flying apart in opposite directions with relativistic velocities at the same time expanding. A comparison of the calculations with unusual ‘double-humped’ spectra of some radio sources suggests the existence in their nuclei of such double components which are at an early stage of relativistic ejection. In particular the double-humped spectra of 3C 84 and 4C 50.11/NRAO-150 can be interpreted in the proposed model (see Figures 6, 7, 12 and Equations (22), (32)). In this model the ratio of maximum frequenciesv 1m/v 2m should be larger than that of the maximum fluxesF v1m (1)/F v2m (2). The linear polarization of the double-humped spectrum is analysed. It is found under rather specific conditions that at the low-frequency maximum of the spectrum of the type given in Figures 6 and 7 a lower degree of linear polarization is expected than at the high-frequency maximum. In addition, it is natural to expect the appearance of circular polarization in sources with internal largescale relativistic motions. The time variations of the radio flux of some QSS, N-galaxies, and nuclei of Seyfert galaxies can also be interpreted in the suggested model of two clouds of relativistic electrons flying apart in different directions with relativistic velocities while simultaneously expanding. For example, Figure 11 shows the flux variations at 3 frequencies whose ratio is 16:4:1. This picture is similar to the observations of 3C 279 at 3.4 mm, 2 cm and 6 cm, and several other sources (Kellermann andPauliny-Toth, 1968). There have been a number of attempts to explain the flux variations of radio sources in the model of successive, but unrelated outbursts of clouds of relativistic electrons caused by supernova explosions. This model meets many difficulties and seems improbable. In this paper we suggest experimental tests to make a final choice between the model of double components flying apart relativistically and the model of two successive, but unrelated, outbursts from supernovae. If the suggested model of explosions in radio sources is correct, then the processes of variable energy output in such different populations as QSS, N-galaxies, radio-galaxies and the nuclei of normal galaxies have a similar nature, differing only in quantity.

Polarization of Obliquely Reflected Waves From an Isotropic Plane‐Stratified Plasma

Abstract: A recently devised realistic model of an inhomogeneous isotropic plane-stratified plasma is examined analytically when electromagnetic waves of both magnetic and electric type are incident upon the layer from below. Properties of the reflected wave are investigated so as to express the characteristics of the polarization ellipse of the reflected wave in terms of the characteristics of the polarization ellipse of the incident wave.

Optical Polarization Measurements of Pulsar NP 0532

Abstract: The linear polarization is of the order of 15 per cent and is variable, and the circular polarization is less than 5 percent.

High power microwave power divider

Abstract: A MICROWAVE POWER DIVIDER IS DISCLOSED WHEREIN MICROWAVE ENERGY AT A FIXED RECTANGULAR WAVEGUIDE INPUT TERMINAL IS SUPPLIED IN VARIABLE RATIOS TO A PAIR OF RECTANGULAR WAVEGUIDE OUTPUT PORTS OF A FIXED OUTPUT ORTHOMODE TRANSDUCER. THE ENERGY INTO THE RECTANGULAR WAVEGUIDE INPUT TERMINAL IS TRANSDUCED TO THE TE11 MODE IN A MODE CHANGE TRANSDUCER CONNECTED TO THE INPUT RECTANGULAR WAVEGUIDE. A FIRST QUARTER-WAVE PLATE TRANSDUCERS THE ENERGY TO A CIRCULAR POLARIZATION MODE. A SECOND QUARTER-WAVE PLATE, ROTATABLE WITH RESPECT TO THE FIRST QUARTER-WAVE PLATE, TRANSDUCES THE CIRCULARLY POLARIZED ENERGY TO A ROTATABLE LINEAR POLARIZATION MODE, THE ANGLE OF POLARIZATION BEING A FUNCTION OF THE ROTARY SETTING OF THE SECOND QUARTER-WAVE PLATE. THE ORTHOMODE TRANSDUCER, FIXED RELATIVE TO THE INPUT TERMINAL, RECEIVES THE LINEAR POLARIZED OUTPUT FROM THE SECOND QUARTER-WAVE PLATE. THE POWER INTO EACH PORT OF THE ORTHOMODE TRANSDUCER IS A FUNCTION OF THE POLARIZATION ANGLE OF THE LINEARLY POLARIZED ENERGY. THE RATIO OF THE POWER SUPPLIED TO EACH OUTPUT PORT IS THEREFORE CONTROLLED BY THE ROTARY SETTING OF THE SECOND QUARTER-WAVE PLATE.

Statistical Characteristics ics of the Polarization Power Ratio for Radar Return with Circular Polarization

Abstract: In this paper, the radar return from a clutter target illuminated by acircularly polarized wave is investigated statistically. The ratio of theenvelope of the left circular component to that of the right circularcomponent of the return signal is formed, and the probability densityfunctions and cumulative distributions of this ratio are found forlinear, square, and logarithmic law detectors. Plots of all densities anddistributions are given for several statistically modeled clutter-typetargets with typical depolarizing and back-scattering characteristics.The probability density functions for the ratio signal from a logaritmicic detector are compared for the cases of circularly and linearlypolarized waves incident on the same clutter-type target. Linearpolarization produces the worst case of spreading of the probabilitydensity function from its median value. Plots are given which indicatethat changes in the amount of depolarization by the clutter cause moresignificant changes in the median value of the polarizationration forlinear than for circular polarization.

Eigenstates of Polarization in Optical Resonators with Partial Polarizers

Abstract: Theoretically and experimentally, the polarization eigenstates in a passive optical resonator with two partial polarizers are shown to be linear. Next to the resonator mirrors, the eigenvectors are orthogonal; between the two partial polarizers they are, in general, not orthogonal. This deviation from orthogonality may explain the observed elliptical polarization of the output of He–Ne lasers with skewed Brewster windows. The results of calculations are shown for the case of a resonator with two equal partial polarizers, each consisting of a plane parallel plate of glass oriented at the Brewster angle and for the case of two different partial polarizers consisting of one and two Brewster plates, respectively. The directions of the eigenpolarizations and the deviation from orthogonality between the polarizers were computed as functions of the skew angle between the polarization axes of the partial polarizers. Within the experimental accuracy, the measured results agree with the theoretical predictions.

Circular Polarization of Jupiter at 9.26 cm

Abstract: THIS communication presents circular polarization observations of Jupiter at a wavelength of 9.26 cm (3,240 MHz).

Circular Polarization Radome Techniques.

Abstract: : A description is given of the effects of anisotropic dielectric gratings on the sidelobe levels of an antenna in a radome for a variety of experimental conditions. These gratings reduced sidelobes levels significantly below those of the radome without gratings. Graphs of the computed transmittance of flat, dielectric sheets are given for circularly polarized waves as functions of frequency. These graphs are useful in determining bandwidths and supplement an earlier report in which transmittance was given as a functional thickness for fixed frequencies. (Author)

Multimode tracking system utilizing a circular waveguide having slots angularly oriented with respect to the waveguide axis

Abstract: Improvement to systems for determining the position of a telecommunications satellite carrying a radiofrequency beacon transmitting signals of circular polarization of a given direction and in which, whenever the beacon is off the boresight axis of a circular horn antenna, the TM01 mode is excited together with the TE11 mode in the circular horn. The TM01 and TE11 modes are separated by a system including a circular feed waveguide for the horn, a pair of rectangular slots formed therein at two diametrically opposite points in a cross section of the waveguide, said slots having their longer sides respectively perpendicular to the direction of the magnetic field at those points of the TE11 mode having said given direction of polarization, two rectangular section guides connected perpendicularly to the circular waveguide and having their long sides respectively parallel to the long sides of the slots so that the slots excite TE10 mode waves in the rectangular waveguide, a magic T having two input waveguides respectively connected to the two rectangular waveguides, an output guide relating to the antisymmetrical waves in the input guides, at whose output the signal relating to the TM01 mode is collected, and an output guide relating to the symmetrical waves in the input guides and comprising an absorber which absorbs the symmetrical waves.

Antenna with conical transmission line feed

Abstract: The apparatus of the present invention provides an antenna with a dual circularly polarized monopulse feed system which employs a conical or angular transmission line to guide a transverse electromagnetic spherical wave to a reflector. For an n element conical transmission line feed where n is a positive integer no less than three, normal modes with phase progressions or delays of 360* /n from one element to the next are used to illuminate the reflector for rotationally symmetric sum patterns with either sense of circular polarization. Similarly, for an n element conical transmission line feed where n is a positive integer no less than five, normal modes with phase progressions or delays of 720* /n from one element to the next are used to illuminate the reflector for rotationally symmetric difference patterns with either sense of circular polarization.

A simple antenna with good circular polarization

Abstract: Simple antenna with good circular polarization over wide space sector, showing geometry, normalized orthogonal field distributions and beamwidth range, considering slot combinations

Elimination of Photomultiplier Gain Shift Due to Extraneous Weak Reversible Magnetic Field

Abstract: In measurements of circular polarization of gamma rays in which the radiation is detected by a scintillator coupled to a photomultiplier, the phototube has to be shielded from the reversible fringing magnetic field of the polarization analyzer. Weak residual fields, however, produce a small gain shift between the photomultiplier outputs during the periods of opposite magnetizations of the polarimeter. By applying slightly different voltages to the photomultiplier simultaneously with reversals of the magnetic field, this shift can be eliminated. A simple effective method of utilizing this suggestion is outlined.

Improvements in or relating to the measurement of circular dichroism

Abstract: 1,173,901. Photo-electric measurement of circular dichroisms. PYE Ltd. March 21, 1967 [March 29, 1966], No. 13801/66. Heading G1A. Circular dichroism is measured by plane polarizing an initially non-polarized beam of radiation, introducing two oppositely sensed circularly polarizing elements alternately into the plane polarized beam to produce alternately two beams circularly polarized in opposite rotational senses, passing the two beams through a sample and directly comparing the intensities of the two beams emergent from said sample. Infrared, visible or ultraviolet light from a variable monochromator 1 is polarized by a Rochon or Wollaston prism 5. The polarized beam is converted alternately into left and right hand circularly polarized light by achromatic circular polarizers 9, 10 alternately inserted in the beam by a drive 11 and passed through a sample 13 on to a photomultiplier 14. The A.C. output of the photomultiplier is synchronously rectified at 15, the polarity and magnitude of the signal produced indicating the sense and magnitude of the circular dichroism of the sample on a centre zero meter or recorder 13. The D. C. output of the photomultiplier is maintained substantially constant by an automatic gain control circuit.