Showing papers on "Circular polarization published in 1992"

Polarization-sensitive low-coherence reflectometer for birefringence characterization and ranging

Abstract: We present a polarization-sensitive optical coherence-domain reflectometer capable of characterizing the phase retardation between orthogonal linear polarization modes at each reflection point in a birefringent sample. The device is insensitive to the rotation of the sample in the plane perpendicular to ranging. Phase measurement accuracy is ±0.86°, but the reflectometer can distinguish local variations in birefringence as small as 0.05° with a distance resolution of 10.8 μm and a dynamic range of 90 dB. Birefringence-sensitive ranging in a wave plate, an electro-optic modulator, and a calf coronary artery is demonstrated.

Use of polarized light to discriminate short-path photons in a multiply scattering medium

Abstract: We describe a method for discriminating short- and long-path photons transmitted through a multiply scattering medium that is based on the relationship between the polarization states of the incident and forward-scattered light. Results of Monte Carlo simulations and experiments show that if the scattering anisotropy of the scatterers is sufficiently small, absorbing barriers embedded in optically dense suspensions of polystyrene spheres can be resolved with good contrast by selectively detecting a component of the scattered-light intensity that has preserved its incident circular polarization state.The principles of operation of a polarization-modulation system capable of measuring small polarization fractions are explained. Using this system we were able to measure polarized light in a depolarized background over 1000 times as large.

Polarization in Electromagnetic Systems

Abstract: Wave polarization principles polarization state representations partially polarized waves antenna-wave interaction dual-polarized systems depolarized media and system applications.

Optical Magnus effect.

Abstract: It is predicted theoretically and registered experimentally that the speckle pattern of a laser beam transmitted through a multimode fiber undergoes an angular shift from the switching of the chirality of the polarization. The effect may be considered as the result of the spin-orbit interaction for the photon in the inhomogeneous medium.

Electromagnetic waves in Faraday chiral media

Abstract: Plane wave propagation in two kinds of Faraday chiral media, where Faraday rotation is combined with optical activity, is studied to examine methods of controlling chirality. The two types of media studied are magnetically biased chiroplasmas and chiroferrites. For propagation along the biasing magnetic field, four wavenumbers and two wave impedances are found which are dependent on the strength of the biasing field. Dispersion diagrams for the chiroplasma case are plotted. Propagation at the plasma frequency of the chiroplasma is also investigated. >

Broadband circular polarization antenna

Abstract: An efficient, lightweight, broadband antenna, having high quality circular polarization capabilities, is disclosed for use in a variety of applications. 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 one 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. In another embodiment, a lightweight material having a dielectric constant less than about 1.5 is employed in the lower resonant cavity and, preferably, in the upper resonant cavity as well.

Stable black self-guided beams of circular symmetry in a bulk Kerr medium

Abstract: We demonstrate the existence of a stable black self-guided beam of circular symmetry in a bulk self-defocusing Kerr medium. There are no gray or higher-order self-guided beams of circular symmetry. The stability of black beams of circular symmetry is in sharp contrast to analogous bright beams in a self-focusing medium, which are unstable. Black self-guided beams are ideal for all-optical devices in bulk material as they can induce a single-mode optical fiber to guide a (weak) signal beam.

Analysis of circular dichroism spectra.

Abstract: Publisher Summary The chapter discusses mathematical methods for the analysis of circular dichroism (CD) spectra. Circular dichroism (CD) is the difference in absorption between left and right circularly polarized light so that CD spectral bands occur wherever there are normal electronic absorption bands in an asymmetric molecule. The chapter focuses on electronic absorption—that is, the spectra that can be measured for a molecule undergoing a transition from its ground electronic state to some higher energy electronic state. Most biological molecules contain a number of electronic units that absorb light nearly independently, called “chromophores,” which are asymmetrically disposed in space. Such asymmetric molecules will absorb left circularly polarized light differently from right circularly polarized light. Thus, CD spectra are usually interpreted empirically, and the chapter discusses two mathematical methods that will help in empirical analysis. Taylor series fitting separates the two distinct types of interactions between chromophores that give rise to CD spectra. For oligomers and polymers, this separation gives insight into the type of secondary structure, facilitates comparison among different molecules, or provides an accurate measure of the changes in a specific molecule when some parameter is altered. Taylor series fitting has been applied primarily to oligo- and polynucleotides as a function of solution conditions. Singular value decomposition (SVD) is an extremely powerful method that can be applied to any series of any type of spectra.

The Zeeman effect in astrophysical water masers and the observation of strong magnetic fields in regions of star formation

Abstract: The present study solves the transfer equations for the polarized radiation of astrophysical 22-GHz water masers in the presence of a magnetic field which causes a Zeeman splitting that is much smaller than the spectral line breadth. The emphasis is placed on the relationship between the recently detected circular polarization in this maser radiation and the strength of the magnetic field. When the observed spectral line breadth is smaller than about 0.8 km/s (FWHM), it is calculated that the uncertainty is less than a factor of about 2. The accuracy is improved significantly when the angle between the line of sight and the direction of the magnetic field does not exceed about 45 deg. Uncertainty in the strength of the magnetic field due to lack of knowledge about which hyperfine transition is the source of the 22-GHz masers is removed. The 22-GHz maser feature is found to be the result of a merger of the three strongest hyperfine components.

Circular dichroism in double photoionization.

Abstract: One-photon two-electron ionization of an atom by circularly polarized light yields triplet differential cross sections different for left and right circular polarization. Necessary kinematical conditions for a finite dichroism are worked out. A numerical calculation for helium which employs correlated wave functions shows the angular correlations of the escaping electron pair to be very different for left and right circular polarization such that the effect should be observable in a coincidence experiment.

Chiral thin solid films: Method of deposition and applications

Abstract: Chiral thin solid films (CTSFs) can be deposited on a solid substrate in vacuum by letting a vapor stream of film material impinge on the substrate at oblique incidence and rotating the substrate during deposition. The direction of substrate rotation determines the handedness of the resulting helical structure which resembles that of a cholesteric or twisted‐nematic liquid crystal layer. CTSFs are useful in making new optical rotators and beam splitters that separate the orthogonal circular polarization components of light. A quadrant‐detector ellipsometer that uses chiral and achiral obliquely deposited thin films is described for measuring the state of polarization of light.

Exact solution for coherent backscattering of polarized light from a random medium of Rayleigh scatterers

Abstract: We discuss a rigorous vectorial theory as a model to represent the enhanced backscattering of polarized light from a random medium. The theory is based on the well known relation between the contributions of the ladder and cyclical diagrams to the intensity which allows to express these contributions in terms of radiative transfer theory. The tensor transfer equation for the electromagnetic field in a half-space occupied by point-like scatterers is explicitly solved with the aid of the Wiener–Hopf method. For the case of normal incidence the angular distribution of the backscattered intensity and the enhancement factor are found for arbitrary angles between the incident and detected linear polarizations and the scanning plane. To describe spatial anisotropy of the backscattering cone the half width at half maximum of the intensity is calculated as a function of these angles. Coherent backscattering of circularly polarized light is also considered.

Coherent-backscatter effect: A vector formulation accounting for polarization and absorption effects and small or large scatterers.

Abstract: Previous theoretical work on the coherent-backscatter effect in the context of speckle time autocorrelation has gone beyond the diffusion approximation and the assumption of isotropic (point) scatterers. This paper extends the theory to include the effects of polarization and absorption, and to give the angular line shape. The results are expressions for angular variations valid for small and large scatterers and linear and circular polarizations, in lossless or lossy media. Calculations show that multiple anisotropic scattering results in the preservation of incident polarization. Application to a problem in radar astronomy is considered. It is shown that the unusual radar measurements (high reflectivity and polarization ratios) of Jupiter's icy Galilean satellites can be explained by coherent backscatter from anisotropic (forward) scatterers.

Quantized complex ferroelectric liquid crystal spatial light modulators.

Abstract: A spatial light modulator design consisting of cascaded or sandwiched layers of ferroelectric liquid crystals (FLC's) is investigated. The interrelation between the FLC material, the polarization of the incident illumination, and the achievable modulation states is characterized. Magnitude modulation is accomplished by standard methods by addressing the FLC layer with linearly polarized light and following it with a properly oriented analyzer. When the FLC is addressed with circularly polarized light, lossless phase modulation results with the phase states separated by twice the angle of rotation of the optical axes. A continuum of elliptical polarization states ties together the lossless phase states achievable by using circular polarization with the more well-known 0 degrees -180 degrees phase states obtainable with linearly polarized light. Layers of various bistable FLC materials can be cascaded, possibly with polarization control layers between some of the layers, to yield a spatial light modulator that produces multip e quantized bits of complex-valued modulation and with independent control of magnitude and phase states. Four-state phase modulation, ternary amplitude-phase modulation, and four-state magnitude modulation are demonstrated experimentally by using two layers of FLC.

Raman optical activity instrument for biochemical studies

Abstract: A simple and fully computer-controlled backscattering incident circular polarization Raman optical activity (ICP ROA) instrument suitable for chioptic studies of biologically significant molecules in aqueous solution is described. It consists of a fast single-stage monochromator equipped with a holographic edge filter, a highly efficient holographic difiaction grating and a thinned back illuminated thermoelectrically cooled charge-coupled device detector as the key spectral elements. A longitudinal electro-optic modulator is employed to switch between orthogonal circular polarization states in the incident laser radiation within a backscattering geometry. A thick Lyot depolarizer is used for the depolarization of the backscattered Raman radiation. High-quality backscattering ICP ROA spectra of (1S)-( − )-trans-pinane, (1R)-( + )-trans-pinane, L-alanine, L-alanyl-L-alanine, lysozyme, D-glucose, α-D-cyclodextrin and 2′-deoxycytidine are presented as typical examples of the excellent performance characteristics.

Chiral reflection from a naturally optically active medium.

Abstract: The differential reflection of left and right circularly polarized light from a naturally chiral liquid was enhanced and quantitatively measured under conditions of total reflection. In accord with recent predictions, the observed signal at the critical angle was some 3 orders of magnitude larger than the intrinsic chiral parameters (~10−7). This is to our knowledge the first observation of molecular optical activity by coherent light scattering.

Nonlinear interaction of an intense electromagnetic wave with an unmagnetized electron—positron plasma

Abstract: The nonlinear interaction of an arbitrarily large-amplitude circularly polarized electromagnetic wave with an unmagnetized electron-positron plasma is considered, taking into account relativistic particle-mass variation as well as large-scale density perturbations created by radiation pressure. It is found that the interaction is governed by an equation for the electromagnetic wave envelope, which is coupled with a pair of equations describing fully nonlinear longitudinal plasma motions. The dynamics of the nonlinear electromagnetic wave packet is studied.

Laser radar device

Abstract: A laser radar system capable of measuring windspeed to within 1 m/s at distances in the range of 10 km. The system comprises two Faraday atomic line filter/detectors combinations (66, 70; 68, 72), a first filter-detector which consists of a metal vapor cell (2) located between crossed polarizers (4, 6). A magnetic field is applied to the cell which Zeeman splits the energy levels resulting in different absorption lines for left and right circularly polarized light. Near these lines the filter acts a a Faraday rotator providing rotary power only in the vicinity of an abosorption line, which provides the 90 degree rotation necessary to pass the second polarizer. At higher fields and vapor densities multiple rotations lead to rapid modulation in the transmission spectrum. Away from the absorption line the filter provides an out of band rejection that is determined by the extinction ratio of the crossed polarizers. By tuning the temperature and the magnetic field in each Faraday filter sharply crossing response curves can be produced. A preferred lasing frequency range is a frequency range covering a portion of one of the slopes of the peak of the first filter and a portion of one of the opposite direction slopes of one of the peaks of the second filter. Within this range an increase in the frequency of signal light will result in a greater fraction of the light detected by one filter-detectors and a smaller fraction detected by the other filter-detector and a decrease in the frequency of the signal light will have the opposite effect. In a preferred embodiment of this invention laser pulses from a laser (52, 54) operating near the midpoint of this preferred frequency range are beamed at a target which could be a windy portion of the atmosphere. Backscattered Doppler shifted light from aerosols and particles in the atmosphere are collected by a telescope (62) and split into two parts, one part being directed to each filter-detector. The intensities of the light detected by the filter-detectors are compared and the relative magnitudes are used to determine the windspeed in the direction of the laser beam. Pulses can be made very short and the travel time of the light is used to determine the range so that a map of windspeed as a function of range is provided in the direction of the laser beam.

Radio continuum and X-ray properties of the coronae of RS Canum Venaticorum and related active binary systems

Abstract: Data from circular polarization measurements are reported which yield radio-continuum and X-ray characterizations of the coronae of active binaries including RS CVn The circular polarization measurements are taken at 6 cm for 28 binary systems detected at flux densities of more than 07 mJy, and the data are examined in conjunction with those by Drake et al (1989) Optical positions are derived for 8 RS CVn objects, three previous detections are confirmed, and seven sources are shown to have circular polarization at levels of 2-13 percent A total of 49 X-ray sources are confirmed in a total of 190 positions, and the correlation between X-ray and radio emissions is analyzed No observational evidence exists to support the notion that radio and X-ray emissions are due to nonthermal electrons, and the data provide evidence for and against thermal gyrosynchrotron radio emission

Strong right-left asymmetry observed in charge transfer from circular atomic states near the matching velocity.

Abstract: A strong right-left scattering asymmetry, depending on scattering angle, has been observed for electron capture by protons impinging on circular states of Na(3{ital P}), excited by circularly polarized light incident perpendicular to the scattering plane. Scattering angles are extremely small, corresponding to grazing incidence collisions. Proton energy is 1 keV, i.e., a collision velocity about half of the orbital velocity of the sodium 3{ital p} electron. The observed asymmetry agrees with recent elaborate theoretical predictions using large atomic basis sets.

Accurate optical measurement of nuclear polarization in optically pumped 3He gas

Abstract: Large nuclear polarizations M (over 80 %) can now be achieved in gaseous 3He by optical pumping. The gas is excited by an RF discharge and is oriented using a high power LNA laser which is lamp pumped and tuned to the 2 3S-2 3P transition at 1.08 μm. In this paper we describe an experiment in which we measure M with high absolute precision. Our method is based on a change as a function of M in the ratio of σ or π polarized light absorbed from a weak probe beam by the 2 3S metastable atoms. The probe was delivered by a diode pumped LNA laser and propagated perpendicular to the direction of the magnetization. Simultaneous measurement of M was made by monitoring the degree of circular polarization $\cal{P}$ of the optical line at 668 nm emitted by the discharge. Our measurements show a linear relationship between M and $\cal{P}$ for all accessible M values and for a wide range of experimental conditions (sample pressure, magnetic field, RF discharge level, etc.). This provides a second method of measurement of the 3He nuclear polarization which is simple to operate and is calibrated and is calibrated over a pressure range of 0.15 to 6.5 torr.

Liquid crystal display element

Abstract: PURPOSE:To increase the using efficiency of light to perform bright positive display with high contrast by using a colorless and transparent lambda/4 phase difference plate and a metallic reflecting plate with hair pin configuration instead of a polarizing plate. CONSTITUTION:A nematic liquid crystal component with negative dielectric anisotropy which include a dichromatic coloring matter is enclosed between 2 sheets of supporting plates 22 and 23 which have transparent electrodes processed by the vertical grading method after SiO diagonal evaporation and the liquid crystal moleculars are made vertical or inclined against the supporting plates 22 and 23 at no voltage. When voltage is applied, the liquid crystal moleculars are made horizontal 30 to uniform their directors and the components arranged in the direction of director of incident light are absorbed to the long axial direction of coloring matter moleculars 32. A component 33 vertical to the direction of directors is transmitted to penetrate it to a lambda/4 phase difference plate 34, reflect it on a metallic plate 37 with hair line configuration as the projected light 36 of circular polarization 36 with right optical activity, penetrate it into the phase difference plate 34 as a circular polarization 38 with left optical activity and then penetrate it into the liquid crystal layer as a straight polarization 39. The straight polarization 39 is absorbed into the coloring matter sufficiently to obtain a projected light 40 which absorbs color completely.

CW doppler lidar

Abstract: A continuous wave Doppler LIDAR with an enhanced signal-to-noise ratio (SNR) that greatly enhances its ability to determine relative fluid velocity. A laser source (12, 50, 102) produces coherent light that is split between a reference beam and a test beam by a beam splitter (16, 106). A quarter-wavelength plate (26, 108) changes the linear polarization of the test beam to a circular polarization. The circularly polarized test beam is focused on a target cell (30) having a very small volume. Any particle in a fluid moving relative to the CW Doppler LIDAR system that passes through the target cell causes a Doppler shift in the frequency of the coherent light reflected from the particle and reverses the rotational direction of circular polarization of the reflected beam. The light reflected from the particle is combined with the reference beam, creating an interference pattern (or difference signal) incident on a photodetector (44, 118). A level detection trigger signal is developed from a corresponding electrical signal produced by the photodetector in response to this difference signal. This level detection trigger signal is used to enable fast Fourier transform processing of the electrical signal only when a particle is within the target cell. The enhanced SNR resulting from the relatively high ratio of the volume per particle to the sensed volume of the target cell thus is not averaged with the low SNR evident when a particle is not in the sensed volume. Consequently, the enhanced SNR provides a much more robust measurement of the particle's relative velocity (and thus the relative fluid velocity) as a function of the Doppler frequency shift in the reflected coherent light caused by the particle as it passes through the target cell.

A Search for Circular Polarization in Cataclysmic Variables

Abstract: The AM Her-type of mass-transfer binary displays strong circular polarization in its optical flux, due to high harmonic cyclotron emission from the vicinity of the accretion shock. Circular polarization is the best direct evidence for magnetic white dwarf primaries in these cataclysmic variable (CV) systems, indicating high field strengths of B≥10 7 G. For more than a decade, we have carried out an optical and infrared polarimetric observing program at Steward Observatory to search for AM Her systems and to detect circularly polarized light in CV systems in which a magnetic white dwarf may be present

Polarization-ellipse rotation by induced gyrotropy in atomic vapors

Abstract: We study theoretically and experimentally a new mechanism for the rotation of the polarization ellipse of a single laser beam propagating through an atomic vapor with a frequency tuned near an atomic resonance. The results of a theoretical treatment for the case of a J = 1/2 to J = 1/2 atomic transition show that a rotation of the polarization ellipse of the laser beam will occur as a result of ground-state optical pumping and that the angle of rotation is independent of the laser intensity over a broad range of laser intensities. The predictions of this theoretical model are tested experimentally through the use of potassium vapor and are found to agree with the experimental data.

Optical mass storage system and memory cell incorporated therein

Abstract: This application relates to a new read-write optical storage technology which is based on the cholesteric liquid crystal (CLC) polymer property of selective reflection at a characteristic wavelength. Each layer in a multi-layer CLC storage arrangement has a different characteristic wavelength, making it possible to randomly select any layer for reading, writing or erasing. Each layer incorporates a plurality of memory cells, in a write/erase mode, disposed on a dye polymer material or having such dye polymer material integrated into the CLC material such that, in the presence of light and electric or magnetic fields, the molecules of the CLC material are heated and align themselves with the electric or magnetic field. To the extent that the CLC molecules align themselves with a magnetic field normal to the plane of a storage element, electromagnetic energy in the form of light or infrared radiation at a specific wavelength, in a read mode, will be reflected. Any other orientation whether due to the presence of a magnetic or electric field or heating alone will be transparent to any other wavelength and a circular polarization opposite to the polarization of an incident reading beam. Finally, a disk storage system and a multi-layered storage system for reading, displaying and printing stored information are shown to indicate applications of the cholesteric liquid crystal storage technology.

Circularly polarized far fields of an axially magnetized circular ferrite microstrip antenna

Abstract: The theoretically derived far-field components of a circular ferrite microstrip antenna (FMA), biased axially by a steady magnetic field, are reported in this letter. The circular polarization, obtained theoretically, is compared with the measured result.

Spin-polarized spontaneous-force atom trap

Abstract: We present observations of a spontaneous-force optical trap in which rubidium atoms are spin polarized by optical pumping. Stable trapping is achieved in two dimensions by the same force as in the Zeeman-shift optical trap, and in the third dimension by a macroscopic vortex force that is insensitive to light polarizations and magnetic fields. When the light along this third direction is circularly polarized and a parallel magnetic field is applied, the atoms become spin polarized.

Construction and performance of BL28 of the Photon Factory for circularly polarized synchrotron radiation

Abstract: A branch beamline, BL28A, has been constructed for the application of circularly polarized vacuum ultraviolet radiation. The radiation can be obtained in the helical undulator operation mode of an insertion device, EMPW♯28, which is also cut for elliptically polarized hard x‐ray radiation. T first harmonic of the helical undulator radiation can be tuned from 40 to 350 eV with its corresponding K value from 3 to 0.2. A monochromator working basically with constant deviation optics was installed, and has started its operation. A circularly polarized flux of ∼1010 photons/s has been achieved with energy resolution of around 500–1000 at the first harmonic peak. The circular polarization after the monochromator was estimated to be higher than 70% by comparing theory and experiment on the magnetic circular dichroism of nickel films in the 3p‐3d excitation region. The design philosophy of the beamline and recent results on the performance tests are presented.

Ionization of Rydberg atoms by circularly and elliptically polarized microwave fields.

Abstract: A classical study of the dynamics of atomic Rydberg states interacting with both elliptically and circularly polarized microwave fields is presented. In recent experiments, enhanced ionization rates were observed in elliptically as opposed to circularly polarized fields. A classical phase-space simulation provides good qualitative agreement with experimental findings. These results are explained in terms of the breakdown of almost conserved quantities as the polarization of the field is changed from circular to elliptical.