Showing papers on "Circular polarization published in 1977"
TL;DR: In this paper, the effects of the nuclear spin-spin interaction with the electronic spins were studied in weak external magnetic fields, of the order of the local field which characterizes the nuclear spins-spin interactions (a few gauss).
Abstract: In a semiconductor, absorption of circularly polarized light (optical pumping) leads to spin-oriented photoelectrons. In this situation, the nuclei of the crystal are dynamically polarized through their hyperfine interaction with the electronic spins. Consequently the electrons experience a hyperfine magnetic field due to the oriented nuclei which may reach several kilogauss. When this large nuclear field is driven obliquely with respect to the direction of the exciting light, the precession of the electronic spins around the nuclear field leads to a decrease of the electronic polarization along the light excitation: it is a nuclear Hanle effect. This work is an experimental and theoretical study of these effects in weak external magnetic fields, of the order of the local field which characterizes the nuclear spin-spin interactions (a few gauss). Large nuclear fields are obtained at 77\ifmmode^\circ\else\textdegree\fi{}K in strongly doped and compensated $p$-type GaAs samples. We present a model which includes the different effects of the hyperfine coupling when there is a nuclear spin temperature among all the nuclei of the sample: Dynamic polarization, nuclear field, but also, existence of an electronic field acting on the nuclei. We show that a small external field is able to drive the large nuclear field acting on the electrons; consequently the electronic polarization is very sensitive to external fields which are too small to have a direct effect on the electronic spin motion. We study experimentally the variation of the electronic polarization with the direction and magnitude of a small external magnetic field, by measuring the circular polarization of the luminescence light. The experimental results are in quantitative agreement with the theoretical predictions. The usual Hanle Lorentzian depolarization curve is strongly modified in low fields and $W$-like singularities appear around zero field. The experimental values of the average electronic and nuclear fields are in reasonable agreement with theoretical evaluations. These nuclear effects may strongly alter the measurement of the Hanle linewidth in standard optical pumping experiments.
370 citations
TL;DR: A measuring system for determining the state of polarization of a beam of light in terms of its Stokes parameters which can be fully automated incorporates a monochromator and single photon counting detection and can be applied over a large wavelength range for very weak optical signals.
Abstract: We describe a measuring system for determining the state of polarization of a beam of light in terms of its Stokes parameters. The technique which can be fully automated incorporates a monochromator and single photon counting detection and can thus be applied over a large wavelength range for very weak optical signals. Fourier transformation of the data by an on-line minicomputer allows immediate calculation of the Stokes parameters. We discuss special applications to light emitted from excited atomic systems with and without cylindrical symmetry.
293 citations
TL;DR: In this paper, the solution to the equation of transfer of polarized radiation in a steady-state homogeneous rarefied medium is applied to self-absorbed synchrotron sources.
Abstract: The solution to the equation of transfer of polarized radiation in a steady-state homogeneous rarefied medium is applied to self-absorbed synchrotron sources. Relativistic electrons (independent of the presence of any cold plasma) can quite easily produce in such sources significant Faraday rotation and/or conversion of linear to circular polarization. Structural inhomogeneities do not obviate the importance of these phenomena in compact nonthermal sources. Contrary to the calculation of Pacholczyk and Swihart (1975), the circular polarization for a homogeneous source changes sign just below the self-absorption turnover as the source becomes opaque, even when polarization conversion dominates; however, for a physically realistic source, structural inhomogeneity may alter this behavior. The observational evidence bearing upon these effects is reviewed.
196 citations
TL;DR: In this paper, an analysis procedure utilizing non-linear least squares techniques is developed that allows one to automate the reduction of measured spectral profiles of the Stokes parameters to determine the field angles, strength as well as other parameters.
Abstract: The application of Unno's (1956) solution of the transfer equation for polarized radiation to the determination of thevector magnetic field is investigated. An analysis procedure utilizing non-linear least squares techniques is developed that allows one to automate the reduction of measured spectral profiles of the Stokes parameters to determine the field angles, strength as well as other parameters. The method is applied to synthetic spectra generated using a model solar atmosphere and yields results of remarkably high accuracy. The influence of additional factors upon determination of the vector field are also considered. These factors include effects of asymmetric profiles, magneto-optical effects, magnetic field gradients, unresolved field elements, scattered light, and instrumental noise.
118 citations
TL;DR: In this article, a paraffin prism was used to measure the longitudinal and transverse shifts of an 8 cm parallel bounded beam of 34.2 GHz (8.77 mm) microwaves.
Abstract: Longitudinal and transverse shifts of an 8 cm parallel bounded beam of 34.2 GHz (8.77 mm) microwaves totally reflected from a paraffin prism have been investigated. The 45°–45°–90° prism is 18 cm high by 25 cm on the sides and the index of refraction is 1.491. Longitudinal shifts as large as 3 cm have been measured in a single reflection near the critical angle for a beam linearly polarized in the plane of incidence. The shift for perpendicular polarization is approximately half this value. The results are in general agreement with the classical theory for the Goos-Hanchen effect. An incident beam polarized at 45° to the incidence plane produces both parallel and perpendicular polarization shifts with values similar to the above. The shifts for both polarizations are reduced but are still distinctly separate if either a second prism or a metallic reflector is brought into the evanescent wave at millimeter distances from the interface. These results are in accordance with stationary phase calculations for two interfaces. It is found that a small (6 mm) transverse shift results if the prism is illuminated with circularly polarized microwaves.
84 citations
TL;DR: The Westerbork Synthesis Radio Telescope was used for observations of solar active regions at 6 cm during 1974 May 8-10 as mentioned in this paper, where the linear polarization was below the noise limit.
Abstract: We have used the Westerbork Synthesis Radio Telescope for observations of solar active regions at 6 cm during 1974 May 8-10. The particular problems of using a sidereal instrument for solar observations are discussed. Maps of total intensity and circular polarization were obtained for four active regions with sunspots and a plage region; the linear polarization was below the noise limit. The brightest components of the 6 cm emission are associated with sunspots, while weaker components are associated with the plage magnetic fields, both longitudinal and transverse. An inversion of the sense of circular polarization was observed in the preceding part of a region with bipolar magnetic-field structure, about two days after the region passed through the central meridian. Nine bursts were also observed, and their one-dimensional positions with respect to the associated active regions are given.
73 citations
TL;DR: In this paper, a transfer procedure based on the coupled-wave formulation was derived, which allows consideration of inhomogeneous sources, and it was shown that plasma characteristic wave eccentricities in a source must be fairly large unless Faraday rotation per absorption depth is very large.
Abstract: As an extension of previous treatments of polarized radiation transfer in homogeneous synchrotron sources, a transfer procedure is derived, based on the coupled-wave formulation, which allows consideration of inhomogeneous sources. It is shown that plasma characteristic wave eccentricities in a source must be fairly large unless Faraday rotation per absorption depth is very large, and that coupling between characteristic waves can be strong in inhomogeneous self-absorbed sources. Calculations are made of the polarized radiation emergent from a source with a boundary of finite thickness. It is found that neglect of propagation effects in the source boundary introduces no significant errors at optically thin frequencies, but that below the self-absorption turnover the emergent polarization may depend significantly upon such effects. In particular, the sign of the circular polarization and the linear polarization position angle depend upon the absorption depth in the boundary region.
58 citations
TL;DR: In this paper, the normal and quadratic Zeeman effect and broad-band circular polarization in white dwarf stars were found to have a positive effect in Grw + 70°8247 whose continuum shows both linear and circular polarization.
Abstract: Searches have been made for the normal and quadratic Zeeman effect and broad-band circular polarization in white dwarf stars. A positive effect has been found in Grw + 70°8247 whose continuum shows both linear and circular polarization.
53 citations
TL;DR: In this article, a modified Mach-Zehnder interferometer employing a linearly polarized scene beam and a circularly polarized reference beam generates signals proportional to the sine and cosine of the phase shift introduced by the plasma.
Abstract: An interferometer has been developed with which it is possible to make accurate plasma density measurements in the presence of density gradients. A modified Mach–Zehnder interferometer employing a linearly polarized scene beam and a circularly polarized reference beam generates signals proportional to the sine and cosine of the phase shift introduced by the plasma. The differential sensitivity of the phase shift measurements is independent of the instantaneous phase angle, and the phase angle may be unambiguously followed through multifringe excursions of the interferometer. The phase shift measurement is also independent of fringe contrast fluctuations caused by the refractive bending of the scene beam by the plasma.
50 citations
TL;DR: In this article, the authors define the complex signal s = x + jy, associated with a real signal having two orthogonal components x and y. This signal follows simple transformation rules when the measuring coordinate system is changed.
Abstract: We define the complex signal s = x + jy, associated with a real signal having two orthogonal components x and y. This signal follows simple transformation rules when the measuring coordinate system is changed. Then we divide it into two other complex signals s+ and s− of opposite polarities, and we study the correspondence which exists between s+ and s− and the concept of an analytical signal. We demonstrate that the polarization parameters of the original signal are given by very simple expressions in terms of s+ or s− or in terms of their Fourier transforms S+ and S−. When the Fourier analysis is made on S+ and S−, the ellipticity, the sense of rotation, and the orientation of the major axis of the polarization ellipse are easily displayed as a function of frequency. The results are valid whatever the coordinate system in which the signal has been measured, even when this system is rotating with respect to a fixed frame of reference (as is often the case for space measurements). In the case of a three-dimensional signal an instantaneous polarization vector is defined, whose components are Pk = |SιJ+|² - |SιJ−|². When it is integrated over time or frequency, this definition conserves the power of the signal and does present the correct relationships with the imaginary part of the coherency matrix. Applications of this formalism to the polarization analysis of artificial and natural signals are presented. Both numerical and analog procedures for obtaining the two circular components of the polarized power are described. When it is applied to the study of ULF waves, this method demonstrates the complexity of the polarization pattern of Pc 1 events.
49 citations
TL;DR: It is found that FDCD can yield the CD for light incident along the direction of the fluorescence transition moment and CPL measurements provide a method for measuring the direction dependent CD or optical activity of a molecule without actually orienting the molecule.
Abstract: The fluorescence detected circular dichroism (FDCD) and circular polarization of luminescence (CPL) of rigid systems is related to molecular parameters. It is found that FDCD can yield the CD for light incident along the direction of the fluorescence transition moment. The average CD can also be measured as in a fluid medium. From CPL measurements one can evaluate the optical activity for light incident along the direction of the absorption transition moment. Thus, photoselection provides a method for measuring the direction dependent CD or optical activity of a molecule without actually orienting the molecule.
TL;DR: In this article, the dependence of the emitted Stokes vector on coronal magnetic field direction, electron density, and temperature and on the height of origin of coronal Fe XIV ions is investigated.
Abstract: Coronal magnetic fields influence in the intensity and linear polarization of light scattered by coronal Fe XIV ions. To interpret polarization measurements of Fe XIV 5303 A coronal emission requires a detailed understanding of the dependence of the emitted Stokes vector on coronal magnetic field direction, electron density, and temperature and on height of origin. The required dependence is included in the solutions of statistical equilibrium for the ion which are solved explicitly for 34 magnetic sublevels in both the ground and four excited terms. The full solutions are reduced to equivalent simple analytic forms which clearly show the required dependence on coronal conditions. The analytic forms of the reduced solutions are suitable for routine analysis of 5303 green line polarimetric data obtained at Pic du Midi and from the Solar Maximum Mission Coronagraph/Polarimeter.
TL;DR: In this article, the angular distribution and frequency dependence of radiation scattered by a spatially degenerate atom undergoing collisions are derived using a previously developed formalism of the quantum theory of line broadening for an atom in its rest frame.
Abstract: Explicit expressions for the angular distribution and frequency dependence of radiation scattered by a spatially degenerate atom undergoing collisions are derived using a previously developed formalism of the quantum theory of line broadening for an atom in its rest frame. Results valid in the impact regime for resonant scattering are presented for the cases of linear incident and scattered polarization circular incident and linear scattered polarization, and unpolarized incident radiation with no monitoring of the scattered polarization. These results relate to scattering involving a j - j + or - 1 - j atomic transition, with lower-state interactions neglected; the expressions obtained take a relatively simple form involving atomic multipolar relaxation rates of the order of k = 0 and k = 2. The angular distributions for each case are combined with the frequency dependences to yield a three-component frequency redistribution function for an s-p-s transition, the components being a coherent term, a frequency-redistributed term with the same angular dependence as the coherent term, and an isotropic frequency-redistributed term.
TL;DR: In a strong magnetic field, the vacuum becomes birefringent as discussed by the authors, and this effect is especially important for pulsars at X-ray wavelengths, especially for magnetic white dwarfs.
Abstract: In a strong magnetic field the vacuum becomes birefringent. This effect is especially important for pulsars at X-ray wavelengths. Any polarized X-ray emission from the surface of a magnetic neutron star becomes depolarized as it propagates through the magnetic field. The soft X-ray emission from AM Her, believed to be a magnetic white dwarf, may show about one radian of phase retardation. In this case, circular polarization of the X-ray flux would be a characteristic signature of vacuum birefringence.
TL;DR: In this article, the parity violation in the neutral weak interaction was detected by observing a helicity dependence in the 6 2P12−72P12 absorption when the laser light is circularly polarized.
TL;DR: In this article, the authors investigated the grazing-angle scattering of fast ions from solid surfaces and established that the circular polarization of light emitted from the scattered ions, and hence the ion orientation, varies strongly with the ion scattering angle.
Abstract: We have investigated the grazing-angle scattering of fast ions from solid surfaces. We establish that the circular polarization of light emitted from the scattered ions, and hence the ion orientation, varies strongly with the ion scattering angle. We show that the nearly elastic ion-surface collisions produce maximum allowed orientation of states with very small alignment.
TL;DR: In this article, a coude photon-counting polarimeter with a Fabry-Perot interferometer is presented, which attains a high resolution of 0.086 A. A description of the instrument is given, with a discussion of various sources of systematic error in polarimetry.
Abstract: We have constructed a coude photon-counting polarimeter capable of attaining (with a Fabry-Perot interferometer) a high resolution. A description of the instrument is given, with a discussion of various sources of systematic error in the polarimetry. Observations of linear and circular polarization in the spectrum of the Ap star ..beta.. Coronae Borealis, throughout the magnetic cycle, are obtained across an Fe II and a Sm II line at a resolution of 0.086 A. Inferences are drawn regarding the magnetic geometry of the star: the geometry appears to be devoid of any symmetry but can probably still be approximated by a decentered dipole model. The longitudinal magnetic curve of the star is derived from the available data.
Abstract: Measurements are reported on the photoelectron spin polarization and ratio of the ion count rates for linearly and circularly polarized light obtained in two-photon ionization of caesium atoms via the 72P1/2 and 72P3/2 intermediate resonance states. Depending on the pulse length of the radiation used the transitions have to be described either in the fine-structure or in the hyperfine-structure coupling scheme. A simple model is used to describe intermediate cases. From these measurements ratios are obtained for the various bound-free matrix elements.
Journal Article•
TL;DR: In this article, a pulsed source of polarized electrons with high intensity and repetition rate is described, which uses the Fano effect on rubidium, and it gives 12 ns pulses of 2.2 × 10 9 electrons with a repetition rate of 50 Hz and a polarization of (65±5)%.
TL;DR: In this article, the nonlinear propagation of an intense circularly polarized electromagnetic wave in a cold plasma is investigated and a relativistic modulational instability and exact localized solutions are found.
01 Dec 1977
TL;DR: In this article, the authors predict large fractions of circular polarization of light emitted by ions scattered from surfaces of ferromagnetic single crystals, which is the case of Ar+ ions from the (110) plane of a Ni single crystal.
Abstract: From a theoretical analysis we predict large fractions of circular polarization of light emitted by ions scattered from surfaces of ferromagnetic single crystals. Maximum enhancement of circular polarization as compared to surface ion scattering from non-magnetic materials is again expected at grazing incidence. A circular polarization of 89% was estimated for the case of Ar+ ions scattered from the (110) plane of a Ni single crystal.
TL;DR: In this paper, the authors measured magnetic-field-induced circular polarization of the center emission in Kl, KBr, and KCl at 1.9 K in fields up to 80 kG.
Abstract: We have measured magnetic-field-induced circular polarization of the $F$-center emission in Kl, KBr, and KCl at 1.9 K in fields up to 80 kG. Both diamagnetic (field-dependent) and paramagnetic (spin-dependent) effects have been observed. The latter requires a special technique in which the pump beam is modulated between right and left circular polarization. The expected behavior as a function of the frequency of the modulation has been observed. We have also measured the spin-lattice relaxation time in the relaxed excited state in KI and KBr for $B\ensuremath{\ge}50$ kG. All the previous measurements indicate a value of the spin-orbit splitting, $|\ensuremath{\lambda}|$, of the order of 1 meV, which is considered a surprisingly small value from purely theoretical grounds.
TL;DR: In this paper, the optical properties of spheroidal grains with resonant impurities are treated, using a model which takes account of the interaction of the resonant atom with the host material that surrounds it.
Abstract: The optical properties of grains with resonant impurities are treated, using a model which takes account of the interaction of the resonant atom with the host material that surrounds it. Such grains are often suggested as the origin of the diffuse interstellar bands. With this ''embedded-cavity model,'' extinction cross sections, linear polarization, and circular polarization are found analytically for spheroidal particles that are small compared with the wavelength. This treatment provides an effective bulk dielectric constant for the composite material that can be used to calculate the optical properties of grains of arbitrary size compared with the wavelength and arbitrary shape. The results differ somewhat from previous predictions, at least for particles small compared with the wavelength. The frequency of peak absorption is shifted, and the absorption exhibits an asymmetry in the sense that it is anomalously weaker on the red side of the line, thus appearing as a ''red emission wing.''
TL;DR: In this paper, the authors investigated the incoherent effects of a plane electromagnetic wave passing through a rain slab, in particular the signal scintillation with their polarization properties, and the amplitude and phase distortions.
Abstract: Signal fluctuations have been frequently observed in radio links using millimeter wavelengths, during atmospheric precipitations. Such fluctuations can be due to the single and multiple scattering by particles which in their motion induce, in the receiving antenna, spurious signals of random amplitude and phase. This paper presents some theoretical results of a first investigation of the incoherent effects for a plane electromagnetic wave passing through a rain slab. In particular it was considered the signal scintillation with their polarization properties, and the amplitude and phase distortions. A coherent circularly polarized incident wave is supposed to propagate normally to a slab of uniform rain constituted by a polidispersion of spherical drops. The computational procedure based on the transfer equation consists of an iterative method able to evidence the four Stokes parameters due to the sequential scattering processes. It is described the dependence of these phenomena upon the frequency, the rain rate, the antenna characteristics and the rain depth and a simple procedure to evaluate the incoherent to coherent power ratio at the antenna frontend is outlined.
TL;DR: In this paper, the spin-polarized spectrum of electrons photoemitted by circularly polarized light in tungsten was calculated based on a three-step model and involves a group-theoretical analysis of the direct optical excitations and their joint density of states.
Abstract: We have calculated the spin-polarized spectrum of electrons photoemitted by circularly polarized light in tungsten. Results are given for free and cesiated surfaces along the (100) and (111) directions. In the (110) direction there is no spin polarization. The calculation is based on the three-step model and involves a group-theoretical analysis of the direct optical excitations and their joint density of states. 100% polarization is predicted for certain photon energy regions.
Patent•
01 Sep 1977
TL;DR: In this article, a laser beam or the like is circularly polarized and directed to two or more retroreflectors and then to a detector, and the relative direction of motion of the retro reflectors is made from the increase or decrease of frequency of beats of one beam against the other.
Abstract: Methods and apparatus are disclosed for studying motion of an object or element, to determine not only quantities of motion but also direction of motion. A laser beam or the like is circularly polarized and directed to two or more retroreflectors and then to a detector. Beams of different frequencies are established and determination of relative direction of motion of the retroreflectors is made from the increase or decrease of frequency of beats of one beam against the other. In one embodiment, left and right circularly polarized light is reflected, and one of the beams is frequency-shifted. The light, being circularly polarized, is insensitive to rotational orientation of the test object, while maintaining directional and motion information.