Showing papers on "Circular polarization published in 1991"

Energy and angular electron spectra for the tunnel ionization of atoms by strong low-frequency radiation

Abstract: The analytic expressions for the probabilities of tunnel ionization of atoms and atomic ions and for the energy and angular electron spectra in a strong low-frequency electromagnetic field are obtained. The adiabatic approximation of quantum mechanics is used. The cases of linear and circular polarization of the field are considered.

On the circular polarization in pulsar emission

Abstract: A model explaining the existence and properties of the circular polarization in pulsar emission is offered. It is based on the properties of waves excited in pulsar magnetospheres by possible plasma instabilities. The cyclotron instability developing due to the anomalous Doppler effect is carefully investigated. The following characteristics of the emission polarization are explained : if circular polarization exists it should be confined to small angles and observed in the core-type emission; the maximum intensity of circular polarization in the profile window is near the intensity maximum of the core-type emission; the sense-reversals of circular polarization in some pulsars and their absence in others; the correlation between circular polarization and position-angle swings; the behaviour of circular polarization in PSR 1541+09, 1702−19 and others

A slot design for uniform aperture field distribution in single-layered radial line slot antennas

Abstract: A single-layered radial line slot antenna (RLSA) is proposed for a direct broadcast from a satellite (DBS) subscriber antenna. It utilizes a radially outward-traveling wave and the aperture field is intolerably tapered if the uniform slots are used. Two novel techniques are applied. First, the slot design for uniform aperture field distribution is introduced. Second, the radial line is terminated by a matching spiral, in place of a dummy load. It suppresses reflection and radiates all the residual power in circular polarization. For a model antenna of 600-mm diameter, the efficiency of 65% is observed. >

Extremely low-profile helix radiating a circularly polarized wave

Abstract: It is shown that the combination of low pitch and a small number of turns realizes a low-profile helix as a radiating element of circular polarization. A two-turn helix of 4 degrees pitch angle shows a bandwidth of 12% for a 3 dB axial-ratio criterion. The numerical results presented lead to new aspects of a low-pitch helix as an effective radiating element. >

An X-Ray Phase Plate Using Bragg-Case Diffraction

Abstract: An X-ray phase plate using two-beam Bragg case diffraction is proposed. The variation of the polarization state of the transmitted (forward-diffracted) beam through the incident angle was observed. Left-handed and right-handed circular polarizations whose degree of circular polarizations were ±0.90 were experimentally produced.

Compact duplexer-polarizer with semicircular waveguide (antenna feed)

Abstract: A light, compact, and high-performance duplexer-polarizer able to generate circularly polarized waves in a circular waveguide is discussed. Two prototypes were built. The standing-wave-ratio (SWR) and ellipticity performances are extremely good (less than 0.15 dB ellipticity over 15% bandwidth). The experimental development was facilitated by the computation of the dispersion curves and of the transverse field distribution associated with the two fundamental guided modes propagating in the different sections of a septum waveguide. >

Theory of natural Raman optical activity

Abstract: A complete theory of natural circular polarization Raman optical activity (ROA) is presented that, for the first time, includes explicit dependence on the polarization and propagation vectors of the incident and scattered photons. The general theory directly yields Raman and ROA intensity expressions for incident, scattered and dual circular polarization (ICP, SCP and DCP) ROA measurements depending analytically on the polar and azimuthal scattering angles and on the orientation angle of an analysing or incident linear polarizer. For the case of chiral molecules, randomly oriented in an optically isotropic phase, two distinct sets of Cartesian Raman and ROA tensors are employed: the isotropic and anisotropic tensor invariants and the set first introduced in the original formulation of (ICP) ROA. In the general theory ten complex ROA invariants are present in any complete tensor set. It is found, however, that only the imaginary parts of six independent invariant combinations may be obtained by natural cir...

Elliptical-polarization analyses of synchrotron radiation in the 5–80-eV region with a reflection polarimeter

Abstract: The Stokes parameters, which completely represent the polarization state of light, have been measured in the 5–80-eV energy region for synchrotron-radiation beams on the VUV to soft X-ray beamlines at the Photon Factory. Various states of polarization were produced for the emerging beam by deflecting the incoming beam vertically with respect to the entrance slit of the monochromator with a premirror of the beamline. The resultant beam was polarization-analyzed using a polarimeter comprising two triple-reflection polarizers. Increasing the beam-deflection angle was found to result in a change in the polarization state from predominantly horizontal linear polarization to elliptical polarization. This procedure could be used both to produce and to verify circular polarization with | P c | ≳ 80% in the energy range 60–80 eV, which could be immediately applied to MCD experiments. Unpolarized light could clearly be distinguished from circularly polarized light. The unpolarized component was found to become larger with increasing energy on a soft X-ray beamline; this was shown to be mainly due to scattering by beamline optical elements.

Observation of magnetic circular dichroism in uv photoemission from ferromagnetic fcc cobalt films

Abstract: We report the observation of effects due to spin-orbit interaction in angle-resolved photoemission from an itinerant ferromagnet (fcc cobalt) using circularly polarized vuv synchrotron radiation. The photoelectron spectra of the Co 3d-band region are found to depend on the relative orientation of the sample magnetization and the photon spin. This effect may be understood as a form of magnetic circular dichroism appearing in the uv photomission regime. It may be used to investigate magnetic phenomena in ferromagnets without performing an explicit spin-polarization analysis.

Theoretical study of radar polarization parameters obtained from cirrus clouds

Abstract: A theoretical investigation of radar polarization parameters that characterize cloud ice backscattering is presented. The parameters considered were those commonly used in radar polarimetrics such as differential reflectivity (ZDR), linear depolarization ratio (LDR), circular depolarization ratio (CDR), intrinsic degree of orientation (ORTT) as well as conventional reflectivities. Experimental data on the shapes of ice crystals and their orientations are taken into account. Results suggest that prolate-shaped scatterers can be distinguished from those having oblate shapes by analyzing the depolarization ratio dependence on the elevation angle. Calculations suggest that circular polarization parameters provide stronger signals in a cross-polar channel and also show a 1esser dependence on scatterer orientation in comparison with linear polarization parameters. Propagation effects do not significantly affect the polarization parameters for equivalent water contents and cloud thicknesses that are typ...

Large enhancement of polarization observed by extracted electrons from the AlGaAs-GaAs superlattice

Abstract: We have observed a large enhancement of the spin polarization of electrons extracted from an AlGaAs-GaAs superlattice illuminated by circularly polarized light. A polarization of 71.2 \ifmmode\pm\else\textpm\fi{}1.1(stat)\ifmmode\pm\else\textpm\fi{}6.1(sys)% was obtained with a photon wavelength of 802 nm at room temperature. We have also confirmed the removal of the degeneracy between a heavy-hole band and a light-hole band at the \ensuremath{\Gamma} point from the laser-wavelength dependence of the polarization.

Parametric instabilities of circularly polarized large-amplitude dispersive Alfvén waves: excitation of parallel-propagating electromagnetic daughter waves

Abstract: We investigate the parametric decay and modulational instabilities of a large-amplitude circularly polarized dispersive Alfven wave. Our treatment is more general than that of previous derivations based on the two-fluid equations in that we allow for propagation of the unstable daughter waves at arbitrary angles to the background magnetic field, although our main concern in this paper is the exploration of new aspects of propagation parallel to the DC magnetic field. In addition to the well-known coupling of pump waves to electrostatic daughter waves, we find a new parametric channel where the pump wave couples directly to electromagnetic daughter waves. Excitation of the electromagnetic instability occurs only for modulation (k/k0 ≤ 1) and not for decay (k/k0 0) and right-hand (K < 0) polarization. For large k/k0, the electromagnetic channel dominates, while at lower values the electrostatic channel has a larger growth rate for modest values of dispersion, pump-wave amplitude and plasma β. Unlike the electrostatic modulational instability, the growth rate of the electromagnetic instability increases monotonically with increasing pump wave amplitude. This analysis confirms that, for decay, the dominant process is coupling to electrostatic daughter waves, at least for parallel propagation. For modulation, the coupling to electromagnetic daughter waves usually dominates, suggesting that the parametric modulational instability is really an electromagnetic phenomenon.

Broadband circular polarization satellite antenna

Abstract: A broadband, circular polarization antenna is disclosed for use on a satellite. In one embodiment, signals are fed to, or received by, an array of electromagnetically coupled patch pairs arranged in sequential rotation by an interconnect network which is coplanar with the coupling patches of the patch pairs. The interconnect network includes phase transmission line means, the lengths of which are preselected to provide the desired phase shifting among the coupling patches. The complexity of the array and the space required are thus reduced. In the described embodiment, two such arrays are employed, each having four patch pairs. The two arrays are arranged in sequential rotation to provide normalization of the circularly polarized transmitted or received beam.

Apparatus for scanning drum inner face and method of scanning therefor

Abstract: The present invention allows image recording with plural light beams while eliminating alignment changes of light spots on the inner face of a drum. A light beam output unit 212 combines two circularly polarized light beams having opposite handedness to each other to produce a composite light beam CB. A polarization beam splitter 203 and mirrors 205 and 207 change the course of the light beam towards the inner face of a drum 120. A quarter-wave plate 202 and the polarization beam splitter 203 splits the composite light beam to two separate light beams as a function of the handedness of the circularly polarized light. The optical elements 202, 203, 205, and 207 are integrally rotated around the axis of the drum 120 by a main scanning motor 230, thus scanning a photosensitive material 110 held on the inner face of the drum 120 with the light beams.

A microstrip line on a chiral substrate

Abstract: Right and left circular vector potentials are developed and used in a spectral-domain solution for a microstrip transmission line on a chiral substrate. These vector potentials have properties similar to those of the usual magnetic and electric vector potentials, except that they result in circular rather than linearly polarized fields, thereby simplifying field expansions in chiral media. The chiral microstrip line does not have bifurcated modes like other chiral guided wave structures; however, the chiral substrate causes a significant asymmetry in both the fields and currents. >

Vector statistics of multiply scattered waves in random systems

Abstract: Statistical distribution functions are derived for the polarization of optical waves transmitted through a random medium. Excellent agreement is obtained with experiment. Our most significant result is the distribution function for the ellipticity \ensuremath{\epsilon}, the ratio between the major and minor axes of the elliptically polarized scattered light. This has a maximum at \ensuremath{\epsilon}=0 and vanishes for \ensuremath{\epsilon}=1, indicating that linear polarization is the most probable state and that circular polarization has vanishing probability. The averaged ellipticity is found to be 〈\ensuremath{\epsilon}〉=1-ln2=0.307.

Variation of the polarization ratio for rotationally inelastic collisions with laser selected velocity

Abstract: We extend the technique of velocity selection by narrow linewidth laser excitation by measuring the polarization of emission following energy transfer as a function of selected velocity. We apply this to rotationally inelastic collisions in A1ΣuLi2–Xe and find that for most transitions, there is a noticeable decrease in the circular polarization ratio at the center of the Doppler profile. We speculate as to whether the reason for this is dynamical, geometrical, or a combination of the two. We are able to deconvolute cross sections for the transfer of orientation as a function of relative speed which can then be compared with cross sections for the transfer of population.

Broadband reset-free automatic polarization controller

Abstract: We demonstrate a novel optically broadband polarization transformer that allows reset-free endless polarization control by means of a simple analog feedback loop. Unlike the narrowband controller in Ref. 1, the present transformer can be operated with broadband light sources and is electro-optically tunable over a wide wavelength range.

A New Scattered Circular Polarization Raman Optical Activity Instrument Equipped with a Charge-Coupled-Device Detector

Abstract: A simple and fully computer-controlled scattered circular polarization Raman optical activity (SCP-ROA) instrument is described which consists of a fast single monochromator and a thermoelectrically cooled charge-coupled-device (CCD) detector as the key spectral elements. A conventional circular analyzer, formed by a quartz zero-order quarter-wave plate attached to a motorized 360° rotator and a fixed linear dichroic sheet polarizer, is employed for the modulation between orthogonal circular polarization states in the scattered radiation within a right-angle scattering geometry. Well-resolved depolarized SCP-ROA spectra of (1S)-(–)-α-pinene and (R)-(+)-pulegone are presented within the wave-number region of ∼550 to 1200 cm−1 as typical examples of the excellent performance of this novel multichannel ROA instrument.

Method of detecting angle of optical rotation in solution having time-dependent concentration, detection apparatus therefor, and detector cell therefor

Abstract: In a detection apparatus, a linearly polarized light beam polarized in a polarizer (62) is converted by being transmitted through a Pockels cell (60), driven by an alternative voltage, into an alternative linearly polarized light beam and a circularly polarized light beam, which is transmitted through a sample solution flowing through a flow cell (68). The transmitted light beam is separated into two polarized light components, and an intensity thereof is measured to obtain a signal proportional to an angle of rotation by the sample solution. A signal corresponding to an angle of rotation caused by an optical rotary power of the sample solution is obtained by subtracting the signal obtained during irradiation of the circularly polarized light from the signal obtained during irradiation of the linearly polarized light. The sample solution (18) is infused into an optical path of the flow cell (68) under a condition where mean velocity is 0.5 to 5 m/sec.

Production and direct measurement of circularly polarized vacuum‐ultraviolet light with multireflection optics

Abstract: The conversion of linearly polarized synchrotron radiation to circular polarization has been successfully achieved beyond the LiF transmission cutoff in the vacuum ultraviolet by utilizing a triple‐reflection polarizer as a quarter‐wave retarder. The Stokes parameters of the emerging beam were directly measured at 30 eV with a reflection‐type polarimeter as a function of the rotation angle of the ‘‘circular polarizer’’ around the optical axis. The results show that a degree of circular polarization of up to ∼±82% was attained at ∼±25° rotation angles, respectively, between the incidence plane for the polarizer and the horizontal plane. This result is in good agreement with a calculation which took into account the independently measured Stokes parameters of the incoming beam.

Light wave polarization determination using a hybrid system

Abstract: Apparatus and method for determining dynamically the polarization vector direction, or polarization vector components and associated temporal phase angle, of a light beam. The apparatus includes a compact polarization beam splitter that receives a beam of light, separates the beam into two perpendicular polarization components and directs these components to a pair of optical detectors and associated circuits that form the sum and difference signals of the electrical signals produced by the optical detectors. This produces a projection of the polarization vector on a given direction. If the light is generally elliptically polarized, use of two such polarization beam splitters and four optical detectors allows reconstruction of the polarization ellipse for the light beam. Alternatively, use of one such polarization beam splitter, two optical detectors and a rotating wave plate in a multiplexed configuration allows reconstruction of the polarization ellipse. The polarization detector is very compact and may be housed in a container that is no more than a few cm. in diameter.

Simple formulae for circular-polarization axial-ratio calculations

Abstract: Some simple, approximate formulas are provided for calculating the axial ratio of a circularly polarized (CP) wave, as generated by two radiating elements that have amplitude, phase, orthogonality, and polarization errors. The derivations of the formulas are not presented, but agreement between the exact and approximate results is demonstrated for a set of sample cases, assuming that the above errors are small. >

Technique for separating electromagnetic refracted signals from reflected signals in down hole electromagnetic tools

Abstract: In a method and apparatus for well logging use, an antenna (40) is supported in a sonde (10) and the transmitted electrical wave has circular polarisation. The apparatus comprises: (a) transmitter means (34) for forming a signal to be transmitted; (b) transmitter antenna means (40) connected to said transmitter for forming a transmitted signal, said antenna means forming a signal having circular polarization. (c) receiver antenna means (36) for receiving a signal return by formations adjacent to the well borehole as a result of operation of said transmitter; (d) said receiver means further including means responsive to polarization of the received signal thereat wherein the polarization indicates reflected or refracted waves.

Polarization of Jovian hectometric emission

Abstract: We have studied the polarization properties of the Jovian hectometric (HOM) emission observed in the low-frequency band 1.2-1326 kHz by the planetary radio astronomy (PRA) experiment aboard the Voyager spacecraft. We have shown that the complex morphology of HOM can be explained by simultaneous radiations from two independent 100% oppositely polarized sources. Analysis of data recorded under different antenna-source configurations indicates that the existence of a linear component in HOM is very unlikely. We show that the apparent degree of circular polarization measured by the PRA instrument, which practically ranges from −1 to +1, is the result of fluctuations in the relative intensities of the two HOM circular components.

Pairing effect of photons in nonlinear polar crystals

Abstract: It is shown that photons in a polar crystal with a high nonlinearity can feel an attractive effective interaction by exchange of virtual phonons. A coherent state is unstable with respect to such an interaction, and a superguiding state is formed through the association of photons in pairs with opposite wave vectors and spins. The photon pairs travel without scattering attenuations. If the photons propagating in a wave guide enter the superguiding state, the wave guide exhibits an ultralow energy loss.

Edge detection for magnetooptical data storage.

Abstract: The polarization sensitive optical heterodyne methods used to detect polarization rotations in conventional magnetooptic data storage systems can be altered to produce nonzero electronic signals only when the polarization rotation changes. Such systems detect the edges of the magnetic domains optically and produce signals similar to conventional inductive magnetic recording channels. Both theoretical and experimental results indicate that optimized edge detection systems can have a performance comparable with present level detection systems but with less complexity. The maximum carrier-to-noise ratio (CNR) occurs for domains 1.3 μm in length when edge detection is used, and the CNR found experimentally at this maximum is 47 dB, comparable to level detection for this size domain.

Dual-spiral slot antennas

Abstract: Two types of dual-spiral slot antennas characterised by their simple feed are studied; one is a bidirectional radiation type (Bi-DSS) and the other is a unidirectional type (Uni-DSS). The radiation characteristics of the Bi-DSS are evaluated using the numerically determined magnetic current distribution. It is found that a travelling wave magnetic current distribution becomes dominant for a particular range of slot-arm lengths, contributing to the radiation of a circularly polarised wave. On the basis of the investigation of the Bi-DSS radiation mechanism, the Uni-DSS antenna with a triplate configuration is designed. Formation of a circularly polarised, unidirectional beam is experimentally realised. A 4 × 8 Uni-DSS array antenna with a simple feeding system is constructed, achieving an aperture efficiency of 60% over a frequency range of 11.6 GHz to 12.0 GHz.

Projection type liquid crystal projection system

Abstract: PURPOSE: To improve the visibility of a picture displayed on a screen. CONSTITUTION: As for a projection type liquid crystal projection system, the projection light of a display color image(linearly polarized light) is converted to right circularly polarized light or left circularly polarized light by a λ/4 wavelength plate 3 and the screen 4 is constituted of the cholesteric liquid crystal 4a, 4b and 4c of right spiral pitch or left spiral pitch which reflect the right circularly polarized light or the left circularly polarized light of the light of R, G and B. Besides, a fluorscent lamp 5 is covered with the filter 6 of the cholestric liquid crystal where the left circularly polarized component or the right circularly polarized component of the external light irradiating the screen 4 is transmitted and which converts the light of the lamp 5 installed on the inside of a house to the left circularly polarized light or the right circularly polarized light. Then, the light of the lamp 5 irradiating the screen 4 is transmitted. Thus, since only the almost half of the external light irradiating the screen 4 is reflected or the almost all the light of the lamp 5 irradiating the screen 4 is transmitted, the image on the screen 4 is made clear. Besides, the inside of the house becomes bright by the external light or the light of the lamp 5 and an ordinary life can be obtained. COPYRIGHT: (C)1993,JPO&Japio