Showing papers on "Circular polarization published in 1975"

Parity violation induced by weak neutral currents in atomic physics. part II

Abstract: The first part of this paper gives a detailed account of the evaluation of the electric dipole amplitude induced in alkali one-photon S-S transitions, by the parity violating electron-nucleus short range potential Vp.v. associated with the weak neutral currents. Two methods are presented : the first involves an explicit sum over the contributions of the P-states admixed with the S-states and incorporates the best information available on S-P electric dipole amplitudes. The second method, mathematically more elegant, avoids with the help of Green's function techniques any explicit sum over the P states, and, provided that some spin-orbit corrections are neglected, leads to a fairly simple formula involving Coulomb integrals tabulated in the literature and the interpolated quantum defects for S and P waves. The second part is devoted to a description of possible ways to detect parity violation induced in radiative S-S transitions, with a brief discussion of physical processes which could be a source of experimental difficulty. The last section of the paper deals with a theoretical analysis of the influence of a static electric field on the radiative S-S transitions. An evaluation of the induced electric dipole amplitude in the case of cesium indicates that it will compete with the magnetic dipole amplitude for electric fields larger than 10 V/cm. An interference effect between these two amplitudes gives rise to an electronic polarization in the final atomic state proportional to the vector product of the static electric field by the photon momentum which, in a typical case, could be as large as 64 %; the measurement of this interesting and rather peculiar effect will lead to a determination of the sign of the magnetic dipole amplitude. Moreover parity violation could manifest itself by a dependence of this electron polarization on the state of circular polarization of the incident photon.

Light scattering from rough surfaces: General incidence angle and polarization

Abstract: The amplitudes of the diffracted fields from a rough surface, for light of general polarization and incidence angle, are found by the classical method of Rayleigh and Fano. Explicit formulas are then obtained for the differential reflected intensity of $P$- and $S$-polarized light as well as for the decrease in reflection coefficient of $S$, $P$, and circularly polarized light due to the excitation of surface plasmons. The results are valid to first order in the surface roughness and are confirmed by additional calculations based on other perturbative methods, both classical and quantum mechanical. The discrepanies found in some cases with the recent results of Maradudin and Mills are analyzed and explained.

Brillouin backscattering instability in magnetized plasmas

Abstract: The decay of a circularly polarized electromagnetic wave propagating parallel to an external magnetic field into another circularly polarized electromagnetic wave and an ion acoustic wave in a homogeneous plasma is considered.

Vacuum polarization in laser fields

Abstract: According to quantum electrodynamics the vacuum shows polarization properties because of the presence of virtual electron-positron pairs. These properties are investigated in the presence of an intense plane wave field, such as is produced by a laser. The laser wave is considered as an external prescribed field and its interaction with the electron-positron field is treated without reference to perturbation theory. The vacuum polarization tensor is computed to second order in the fine structure constant in the form of a double integral. For a Dyson equation for the photon propagator is solved by an eigenfunction expansion. For a plane laser wave of infinite extent and circular polarization the results are relatively simple and explicit. Analytical properties of the photon propagator are discussed. The effects of vacuum polarization on an additional weak wave field (a non-laser photon) can be described approximately by two complex indices of refraction.

Electric-field-induced differential scattering of right and left circularly polarized light

Abstract: The differential scattering of right and left circularly polarized light is a manifestation of optical activity. Both naturally optically active systems and fluids in a magnetic field parallel to the direction of propagation exhibit differential scattering. Although there is no electric analogue of Faraday's effect, a static electric field applied to a fluid perpendicular to the direction of propagation induces a difference in the scattered intensities of right and left circularly polarized light. The difference is linear in the field strength. It is determined by the effect of the field on the polarizabilities producing optical activity and is present in all matter, including monatomic gases. The classical theory of the scattering of electromagnetic waves is used in a formulation of the general theory of light scattering in an electric field. Results are given for some particular symmetries, including spherical, tetrahedral and dipolar molecules, and estimates of the magnitude of the effect are made.

Theoretical studies in photoelectron spectroscopy. Molecular optical activity in the region of continuous absorption and its characterization by the angular distribution of photoelectrons

Abstract: The phenomenon of molecular optical activity is examined in the region of continuous absorption. When the "excited" state of the molecule describes an infinite (ionized) system, then the angular distribution of photoelectrons is the sum of coherent contributions corresponding to different magnitudes and interferences of $\ensuremath{\hbar}\stackrel{\ensuremath{\rightarrow}}{1}$, the angular momentum of the photoelectron. The amplitude for such a process is the sum of terms for each $l$; thus, since both even and odd values of $l$ can coexist at a single energy in the continuous spectrum, the electric and magnetic dipole matrix elements can coexist in this amplitude, making possible the existence of electric-dipole-magnetic-dipole interference in the angular distribution even for a molecule with a center or plane of symmetry. For discrete absorption, in which the intensity is the sum of incoherent contributions corresponding to the intensities for populating the fine-structure levels of a given excited state, the coexistence of the electric and magnetic dipole matrix elements in the amplitude is possible only for a molecule with a site which is asymmetric with respect to inversion or reflection; otherwise both even and odd values of $l$ could not coexist at a single energy in the discrete spectrum. The signs of the electric-dipole-magnetic-dipole interference terms are opposite for left and right circularly polarized light; thus there exists a signal for the angular distribution difference for absorption of left and right circularly polarized light of order $\ensuremath{\alpha}$ relative to the angular distribution for absorption of light of either polarization. This is just the phenomenon of "circular dichroism" which characterizes molecular "optical activity" in the region of absorption. It exists for the angular distribution of photoelectrons ejected from an oriented molecule with a center or plane of symmetry, but vanishes for isotropic systems (atoms) owing to the independence of the radial wave functions from the magnetic quantum number. This ensures the orthogonality of atomic radial wave functions belonging to states of different $m$ and is responsible for the selection rule in atomic spectroscopy that magnetic-dipole transitions are possible only between the fine-structure levels of a given multiplet. Measurement of the angular distribution characteristic for this process would provide a sensitive probe of the parameters of the initial molecular orbital. The existence of even-odd-type interferences of the partial waves of the photoelectron would provide a test of the time-reversal invariance of the wave function for the ionized system, since these interferences depend on the sine rather than the cosine of the phase-shift difference and hence on the normalization of the wave function to satisfy incoming boundary conditions. Calculations are carried out to illustrate these and other points.

Effect of elliptically polarized light on the angular distribution of photoelectrons

Abstract: The angular distribution of photoelectrons predicted for elliptically polarized light is shown to be the same as that predicted for partially polarized light having incoherent perpendicular electric field components equal to the electric field components along the major and minor axes of the ellipse.

Spin-Polarized Electrons from Autoionizing Transitions in Thallium

Abstract: The spin polarization of photoelectrons emitted by thallium atoms exposed to circularly polarized light has been measured between 1400 and 1700 \AA{}. The polarization curve shows a pronounced structure which is determined by the autoionization resonances. The results are explained on the basis of Fano's resonance theory.

Coaxial waveguide antenna

Abstract: Disclosed is a coaxial waveguide antenna. In a basic form the coaxial waveguide horn for the antenna comprises an inner section operating in a Σ (sum) mode only and an outer section operating in a Δ (difference) mode only. Where required for broadband (i.e., for more than 1 octave), intermediate sections operating in Σ and Δ modes are provided. The basic structure operates in the linear mode; for polarization diversity and circular polarization, a polarizer is placed in front of the horn, or a dielectric sheet is positioned within a coaxial waveguide section at an angle of 45° as to the E field, or by feeding the coaxial waveguide with six or more number of probes.

Development of polarization magneto-optics of paramagnetic crystals

Abstract: A review is given of the current status of the polarization magneto-optics of crystals with paramagnetic impurity ions. Methods for measuring the magnetic circular anisotropy are discussed and a review is given of the results obtained in recent years by traditional magneto-optic investigations (including the magnetooptic activity in the absorption spectra of intrinsic and impurity defects in crystals, magnetic circular polarization of the luminescence, and anisotropy of the magneto-optic activity in cubic crystals). Attention is concentrated on new methods in polarization magneto-optics, which include investigations of the interaction of the spin system with the crystal lattice, particularly the spin-lattice relaxation and spin memory effects, experiments on radio-optic double resonance, investigations of the optical spin relaxation, nonlinear magneto-optic effects, etc.

Three Photon Ionization of Alkali Atoms at the Ruby Laser Wavelength

Abstract: Single mode ruby laser radiation (694 nm) and an atomic beam apparatus have been used in the study of the three photon ionization of Na, K, Rb, and Cs atoms. The process in all cases is nonresonant, the observations being consistent with a rate given by W3F3 where F is the photon flux. The values obtained for W3l (linear polarization) and W3C (circular polarization) and the ratio W3c/W3l are discussed in relation to recently calculated results and the few other experimental results available. Discrepancies well beyond the assigned errors exist between experimental and calculated results.

Isotope selective excitation and separation method and apparatus utilizing circularly polarized pulsed radiation

Abstract: The isotopes of a gas are separated by using a circularly polarized laser to excite a lower energy level to higher split intermediate energy levels, a second laser pulse of the same circular polarization is applied to said energized gas at a time π/Δω where πΔ is the frequency splitting of the intermediate levels, to excite said excited intermediate levels to a higher energy level where an ionizing field ionizes the atoms or molecules in the higher level so that they may be separated from the un-ionized atoms or molecules of the other isotope.

Measurements of the circular polarization of radio sources at frequencies of 0.63, 1.4, 5.0 and 8.9 GHz.

Abstract: Circular polarization measurements were made with the Parkes 64 m telescope on 66 mainly extragalactic sources, 33 of which were studied at two or more frequencies. Circular polarization was definitely found in the eight quasi-stellar sources PKS0237-23, 0537-441, 1127-14, 1226+02 (3C273), 1253-05 (3C279), 2134+004, 2145+06 and 2345-16, as it was measured at the 4u level or higher in at least two observing sessions.

Improved polarization measurements using a modified three antenna technique

Abstract: An improved three-antenna measurement of polarization that greatly reduces the uncertainty due to phase measurement errors is described. This technique is used to calibrate polarization standards and probes used in near-field antenna measurements. >

Theory of domain wall motion induced by microwave magnetic fields

Abstract: A general theory is developed that applies to arbitrary polarization and takes account of damping and of the dipolar interaction between domains. The effect of the microwave field on the domain structure can be characterized by a pressure on the domain walls and by an alignment energy, both of which are proportional to the square of the rf magnetic field and become large in the vicinity of a resonance. For circular polarization the pressure tends to decrease the Larmor-domains (domains in which the imposed sense of polarization coincides with the sense of the natural spin precession) for frequencies outside the resonance region. Inside the resonance region, however, the pressure tends to increase the Larmor-domains. A linearly polarized field also exerts a pressure on the domain walls, with the polarity dependent upon the orientation of the field to the wall normal. In a linearly polarized magnetic field the domain walls tend to become aligned parallel to the rf field at frequencies ω near the low-frequency resonance (ω =γH a , γ = gyromagnetic ratio, H a = anisotropy field) and perpendicular to the rf field at frequencies near the high-frequency resonance (ω = γ[H a (H a + 4πM 0 )]1/2, M 0 = saturation magnetization).

Design of Ferrite Differential Phase Shift Sections

Abstract: Ferrite differential phase shift sections are useful as nonreciprocal circular polarizers in dual-mode phase shifters, as half-wave plates in precision rotary-field phase shifters, and in other devices where nonreciprocal birefringence is desirable. This paper presents a simple design model that provides accurate estimates of the differential phase shift and frequency dispersion of sections using transverse quadruple magnetic field biasing in a circular waveguide completely filled with ferrite.

Polarization insensitive lens formed of spiral radiators

Abstract: A polarization insensitive lens is disclosed for receiving and reradiating electromagnetic energy, which may be either left-hand circular polarized or right-hand circular polarized or of any linear polarization or, in fact, of any polarization state. Each lens is comprised of a pair of spaced apart multiarm/antenna elements of opposite geometric polarization. The elements are located on opposite sides of a ground plane and spaced therefrom by 1/4 wave length. The arms of each antenna element are constructed such that both right-hand circular polarized and left circular polarized signals received by one element experience the same phase delay while being transmitted and then reradiated from the other antenna element.

The detection of an Halpha Zeeman pattern in the cool magnetic white dwarf G 99-47.

Abstract: An apparent H$alpha$ absorption feature has been detected in image tube scans of the cool magnetic white dwarf G99-47, previously classified as DC (featureless). The broad approx.2.5 A EW line is centered some 21 A shortword from the normal H$alpha$ position. This lines is interpreted as the $pi$ component of H$alpha$-shifted by the quadratic Zeeman effect in a surface field of approx.15x10$sup 6$ gauss. This interpretation is supported by the detection of the characteristic circular polarization of the sigma components at +-350 A in data obtained with the multichannel spectrophotometer. Both results are fitted well by a simple, centered dipole model with a mean longitudinal field of 5.6x10$sup 6$ gauss. However, the longitudinal field strength indicated from the continuum circular dichroism theory is about a factor of four smaller. The strength of the H$alpha$ absorption and absence of other detectable Balmer and Ca ii lines are consistent with G99-47 being a very cool, metal-poor DA star. (AIP)

Intermediate polarization of type I bursts

Abstract: A constant polarization degree was found in groups of type I bursts having intermediate polarization for all the duration of the group. The same circumstance was verified also for analogous bursts present during a type IV event. The consequences of this behaviour, considering also the results of some recent papers, is discussed. The polarization amount is probably intrinsic to the source itself.

Method for altering elliptically polarized light

Abstract: The optical transitions of extrinsically optically active soluble and insoluble materials become circularly dichroic when in contact with twisted nematic liquid crystalline materials. The circularly dichroic optical properties induced in the normally extrinsically optically active materials are utilized to alter the relative amounts of left and right hand circularly polarized light in elliptically polarized light including producing circularly polarized light.

Instabilities in Active Molecular Plasma

Abstract: Some properties of active molecular plasmas are considered in the presence of a strong circularly polarized wave It is shown that the external field may cause new instabilities Furthermore, new instabilities are found in active molecular hot plasmas even in the absence of external electric fields