Circular Polarization Measurements Research Articles

The Measurement of Circular Polarization in the Near-IR Luminescence from Chiral Complexes of Yb(III) and Nd(III)

This work describes the measurement and analysis of circular polarization in the luminescence (CPL), in the near-IR spectral region, from chiral complexes of Yb(III) and Nd(III) in solution. The experimental technique is based upon previous measurements of CPL in the visible region. Instrumentation design, performance, and calibration are discussed. The experimental technique has been applied to several related complexes of Yb(III) and Nd(III) with chiral macrocyclic ligands based on 1,4,7,10-tetraazacyclododecane that have approximate C4 symmetry. In addition, CPL from D3 complexes of Yb(III) with 2,6-pyridinedicarboxylate, which were prepared as a solution of enriched enantiomers by the addition of (+)-dimethyltartrate, is also presented. It is demonstrated that CPL from the 2F5/2 → 2F7/2 transition of Yb(III) at 980 nm is particularly suited for CPL studies because this transition satisfies magnetic-dipole selection rules. The luminescence from the 4F3/2 → 4I9/2 and 4F3/2 → 4I11/2 transitions of Nd(III...

Detection and Measurement of Parsec-Scale Circular Polarization in Four [CLC]AGNs[/CLC

We present five epochs of 15 GHz VLBA observations of 13 AGNs. These observations were specially calibrated to detect parsec-scale circular polarization and our calibration techniques are discussed and analyzed in detail. We obtained reliable detections of parsec-scale circular polarization in the radio jets of four AGNs: 3C 84, PKS 0528+134, 3C 273, and 3C 279. For each of these objects our detections are at the level of approximately 0.3%–1% local fractional circular polarization. Each individual detection has a significance in the range of 3 to 10 σ. Our observations are consistent across multiple epochs (and different calibration techniques) in the sign and magnitude of the circular polarization observed. 3C 273 and 3C 279 both undergo core outbursts during our observations and changes in the circular polarization of both sources are correlated with these outbursts. In general, we observe the circular polarization to be nearly coincident with the strong VLBI cores of these objects; however, in 3C 84 the circular polarization is located a full milliarcsecond south of the source peak, and in the 1996.73 epoch of 3C 273 the circular polarization is predominately associated with the newly emerging jet component. Our observations support the theoretical conclusion that emission of circular polarization is a sensitive function of opacity, being strongest when the optical depth is near unity. Circular polarization may be produced as an intrinsic component of synchrotron radiation or by the Faraday conversion of linear to circular polarization. Our single-frequency observations do not easily distinguish between these possible mechanisms, but independent of mechanism, the remarkable consistency across epoch of the sign of the observed circular polarization suggests the existence of a long-term, stable, unidirectional magnetic field. Single-dish observations of 3C 273 and 3C 279 at 8 GHz by Hodge and Aller suggest that this stability may persist for decades in our frame of observation.

Cyclotron resonance measurements of organic conductor α-(BEDT-TTF) 2KHg(SeCN) 4

α-(BEDT-TTF) 2KHg(SeCN) 4 is the new organic conductor which has been synthesized by Sasaki recently. Although it has similar crystal structure with (BEDT-TTF) 2KHg(SCN) 4, it does not show antiferromagnetic like transition down to 0.5 K. Therefore the comparison of the physical properties of these two substances is interesting. The cyclotron resonance of K-Se salt has been measured in the millimeter and submillimeter wave regions with the pulsed magnetic field up to 15 T at 1.8 K, and we observed only one cyclotron resonance with the effective mass of 0.96 m e. It can be attributed to α-orbit, and this effective mass turned out to be smaller than 2.0 m e obtained by SdH oscillation. The circular polarization measurement has also been performed and this resonance turned out to be hole active which is consistent with the band calculation.

Relativistic Positrons in Nonthermal Radio Sources

We describe a procedure for measuring the contribution of relativistic positrons to radio synchrotron radiation. The method relies on the fact that synchrotron radiation from particles of one sign (e.g., electrons) is circularly polarized by a small but measurable amount. If, on the other hand, there are equal numbers of relativistic positrons and electrons, the net circular polarization is zero. The method is illustrated through high-accuracy mapping of the circular polarization of the Crab Nebula at 610 MHz. No significant circular polarization was detected: a very conservative limit is 0.05%, and a more realistic one is 0.03%. We calculate the degree of circular polarization expected if only electrons are present, allowing for the reduction in polarization resulting from nonuniformities in the magnetic field along the line of sight and across the telescope beam. This reduction due to field nonuniformity is estimated from measurements of the degree of linear polarization at optical and high radio frequencies with similar angular resolution to the circular polarization measurements. We find that the observed upper limit on the degree of circular polarization is comparable to or below that expected if only electrons radiate. Various explanations of this result are discussed, including (1) a weaker than assumed magnetic field, (2) a field preferentially nearly perpendicular to the line of sight, (3) a field structure of such a type that nonuniformities reduce the degree of circular polarization by more than they reduce the degree of linear polarization, and (4) the presence of relativistic positrons. Although explanation 1 is implausible, possibilities 2 and 3 cannot be excluded. If future observations establish that the degree of circular polarization at 610 MHz is less than 0.01%, a contribution from positrons would be strongly favored.

VLBA polarization monitoring of SiO masers towards late-type stars

We have used the VLBA to conduct a monitoring campaign of the total intensity and polarization structure of the 43 GHz, v = 1, J = 1-0 SiO masers from three late-type stars. Our data reveal that rings and arcs of emission are the prevalent total intensity structure observed. Coherent structures are also evident in the linearly polarized emission. Dramatic structural variations are common: images taken 6 months apart often bear little relationship to each other. Based on circular polarization measurements we estimate the typical magnetic field strength at the position of the SiO masers to be ∼5–10 G.

Neptune radio emission in dipole and multipole magnetic fields

We study Neptune's smooth radio emission in two ways: we simulate the observations and we then consider the radio effects of Neptune's magnetic multipoles. A procedure to deduce the characteristics of radio sources observed by the Planetary Radio Astronomy experiment minimizes limiting assumptions and maximizes use of the data, including quantitative measurement of circular polarization. Study of specific sources simulates time variation of intensity and apparent polarization of their integrated emission over an extended time period. The method is applied to Neptune smooth recurrent emission (SRE). Time series are modeled with both broad and beamed emission patterns, and at two frequencies which exhibit different time variation of polarization. These dipole‐based results are overturned by consideration of more complex models of Neptune's magnetic field. Any smooth emission from the anticipated auroral radio source is weak and briefly observed. Dominant SRE originates in complex fields at midlatitude. Possible SRE source locations overlap that of “high‐latitude” emission (HLE) between +(out) and −(in) quadrupoles. This is the first identification of multipolar magnetic structure with a major source of planetary radio emission.

Raman optical activity of simple alanyl peptides: Backscattering in‐phase dual circular polarization measurements in aqueous solution

AbstractWe report the measurement of backscattering in‐phase dual circular polarization (DCPI) Raman optical activity (ROA) for the simple alanyl peptides L‐alanyl‐L‐alanine ([L‐Ala]2), L‐alanylglycine (L‐Ala‐Gly), glycyl‐L‐alanine (Gly‐L‐Ala), and L‐alanyl‐L‐alanyl‐L‐alanine ([L‐Ala]3) in aqueous solutions. Empirical correlations between ROA features and the amino acid composition of the peptides are described. It is shown that the sum of the DCPIROA spectra for L‐Ala‐Gly and Gly‐L‐Ala is nearly the same as the corresponding ROA spectrum for (L‐Ala)2. Additionally, the DCPIROA spectrum for (L‐Ala)2 is very close to that of (L‐Ala)3, as has been observed previously using backscattering unpolarized incident circular polarization (ICPu) ROA. The ROA contributions of the different L‐Ala groups, which occur separately in the two glycyl peptides of alanine and jointly in (L‐Ala)2, are described in terms of the extent of vibrational coupling between peptide subunits. From these results, it appears that ROA has a more local sensitivity to vibrational coupling than is found in VCD or electronic circular dichroism. © 1995 John Wiley & Sons, Inc.

A new method for measuring the retardation of a photoelastic modulator using single photon counting techniques

We present a new method to measure in situ the amplitude of the retardation for a photoelastic modulator polarimeter using single photon counting techniques. The method allows the simultaneous measurement of linear and circular polarization of light without the need for a separate calibration procedure. Comparison with measurements made with a λ/4-retarder polarimeter show excellent agreement, confirming the method used.

Observation of atomic polarization via untilted beam-foil excitation under an external magnetic field

Circular polarization measurements on the λ=468.6 nm light emitted in the4He IIn=3-n=4 transition show that the excited states of ions emerging from anuntilted carbon foil in an external magnetic field are polarized. The polarization is parallel to the external field, increases with the strength of the field until a maximum is reached at ∼ 40 mT, and then decreases.

Circular polarization measurements of Lyman- alpha radiation from the decay of the 22Pj states of hydrogen excited by 54.4 eV electrons

Coincidence measurements are reported for the circular polarization of Lyman- alpha radiation resulting from the decay of 22Pj states excited by electron impact at an incident energy of 54.4 eV in a range of scattering angles from 5'<or= theta e<or=40'. The data were obtained using a recently developed efficient polarization analyser for this spectral line and the statistical significance of the data is much better than for previously reported measurements. The data are analysed to yield values for the coherence parameter P+ and show that spin exchange interactions play a significant, if unexpected, role in the dynamic range investigated.

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

view Abstract Citations (73) References (41) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Radio Continuum and X-Ray Properties of the Coronae of RS Canum Venaticorum and Related Active Binary Systems Drake, Stephen A. ; Simon, Theodore ; Linsky, Jeffrey L. 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 0.7 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. Publication: The Astrophysical Journal Supplement Series Pub Date: September 1992 DOI: 10.1086/191717 Bibcode: 1992ApJS...82..311D Keywords: Binary Stars; Radio Emission; Stellar Coronas; X Ray Stars; Astronomical Polarimetry; Circular Polarization; Very Large Array (Vla); Astrophysics full text sources ADS | data products SIMBAD (77)

High resolution photoabsorption and circular polarization measurements on the University of California/National Laboratory spherical grating monochromator beamline

We have measured the N, C, and O 1s photoabsorption of O2,N2 and CO using the University of California/National Laboratory bend magnet beamline located at the Stanford Synchrotron Radiation Laboratory. The photon-energy resolving power at the N 1s edge ranges from 8–12.5 × 103 based upon the vibrationally resolved 1s-π∗ transition, indicating that this spherical grating monochromator is one of the highest-resolution soft-X-ray/ultraviolet photon sources yet reported. Magnetic circular dichroism was also measured with this beamline on highly magnetized thin films. Left and right elliptically polarized soft X-rays were produced by collecting the synchrotron radiation above or below the plane of the electron ring.

Possible application of circular polarization for remote sensing of cosmic bodies

Phase dependences of circular polarization were obtained with a precision Stokes polarimeter designed and constructed at the Main Astronomical Observatory of AS Ukraine. A study was made of dielectric and metallic powders with grains of diameter 10–100 Μm. Metallic powders were found to produce an essential circular polarization - up to 3%, just as dielectric powders did not show circular polarization values more than 0.05% Change of circular polarization with phase angle V is greatly depended on surface structure. Loose powders give phase curves with the same sign of circular polarization everywhere and with maximum at large phase angles V > 120 ‡. Measurements of compacted powders show curves which change the sign repeatedly and have additional maxima, including a maximum at small phase angles V < 40 ‡. A theory was created which considers a circular polarization as a result of multiple reflections of light from particulate surface. The theory provides reasonable good fit to the experimental data. It was concluded that measurements of circular polarization can be used to find metals in surface material of cosmic bodies (especially asteroids) and to determine characteristics of surface structure, in particular, to establish presence of regolith on metal-rich bodies.

Dual and incident circular polarization Raman optical activity backscattering of (—)-trans-pinane

We report the first measurement of dual circular polarization (DCP) Raman optical activity (ROA). DCP ROA was predicted recently to be a new form of ROA in which the incident and scattered light beams are synchronously modulated between right and left circular polarization states. Using a new backscattering apparatus and (—)-trans-pinane, we confirm the theoretical predictions and compare our results to the conventional incident circular polarization (ICP) form of ROA.

A star-and-sky chopping polarimeter: design and performance

We have developed a star-and-sky chopping polarimeter for accurate measurements of linear polarization of starlight in the standard astronomical photometric U, B, V, R, and I bands. The instrumental polarization, as determined by observing the standard unpolarized stars, is 0.04%. It is possible to use the instrument for the measurements of circular polarization as well. A UNICORN microcomputer controls the various operations of the instrument, acquires the data, and does the on-line data reduction. This paper describes the design and performance of the polarimeter.

The weak magnetic field of the AP star Epsilon Ursae Majoris

view Abstract Citations (28) References (22) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Weak Magnetic Field of the AP Star Epsilon Ursae Majoris Bohlender, David A. ; Landstreet, J. D. Abstract High-SNR circular polarization measurements in the wings of H-beta have been obtained for the bright A0pCr star Epsilon UMa, throughout its 5.0887-d rotation period. These data suggest that Epsilon UMa possesses an approximately dipolar magnetic field with magnetic extrema of +128 and -64 G. If the inclination of the rotation axis of the star is in the range i = 65 + or - 15 deg, then the obliquity of the magnetic field axis to the rotation axis is between 19 and 84 deg. The observations are compared with recent Doppler imaging studies of the surface abundances of Epsilon UMa. Publication: The Astrophysical Journal Pub Date: July 1990 DOI: 10.1086/185771 Bibcode: 1990ApJ...358L..25B Keywords: A Stars; Magnetic Stars; Peculiar Stars; Stellar Magnetic Fields; Circular Polarization; H Beta Line; Magnetic Field Configurations; Magnetic Flux; Stellar Rotation; Stellar Spectra; Astrophysics full text sources ADS | data products SIMBAD (1)

Safety factor on the axis of a tokamak during Ohmically heated sawtoothing discharges from a localized measurement of circular polarization of the Lii 6708 Å line

Analysis of the circular polarization of the Lii 6708 Å line emitted from a monoenergetic lithium beam provides a spatially resolved measurement of the poloidal magnetic field on the Texas experimental tokamak [Nucl. Technol. Fusion 1, 479 (1989)]. Determined from the measured magnetic field, the safety factor on the magnetic axis during Ohmically heated sawtoothing discharges is near unity.

Circular polarisation measurements of the Lα cascade radiation for the 32Dj states of atomic hydrogen, excited by electron impact

Measurements are reported for the circular polarisation of the Lalpha radiation arising from the cascade of the 32Dj states of atomic hydrogen to the 22Pj states detected in coincidence with electrons with n=3 energy loss. Data for the atomic orientation parameter Lperpendicular to are presented at incident electron energies of 54.4 and 100 eV and at scattering angles theta e of 20' and 25'. These data, together with previous measurements for this transition, constitute a determination of the complete parameter set ( gamma ,Pl, rho 00,L perpendicular to ) for 32Dj excitations in this dynamic range. Calculations for P3 and Lperpendicular to using distorted-wave approximation theory are also performed. The theoretical results are presented and compared with the experimental data.

Small Scale Motions Over Concentrated Magnetic Field Regions of the Quiet Sun

Using a time sequence of filtergrams in the magnetically sensitive λ6103A CaI line (with circular polarization measurements), obtained with the SPO Vacuum Tower Telescope and the universal filter we mapped the line of sight velocity and the longitudinal magnetic field in three quiet solar regions. After elimination of the effect of the 5-minute photospheric oscillations we found in two regions of concentrated magnetic field no association with the line of sight velocity, while the third region was associated with small (&lt;300 m/s) downflows.

The optical and near-infrared continuum polarization of five magnetic white dwarf stars - New observations and considerations regarding its origin

Linear and circular broadband continuum polarization measurements throughout the 0.35-1.65-micron spectral region were obtained for GrW +70 deg 8247, GD 229, G240-72, G227-35, and LP 790-29. The continuum is found to be characterized by significant Coulomb modification of the Landau-type autoionization thresholds. The spectral characteristics of continuum polarization originating from a centered dipole field distribution are predicted. The magnetobremsstrahlung model can describe several characteristics of the polarization of Grw + 70 deg 8247, suggesting that plasma eigenmodes draw the resultant continuum polarization away from a photoionization edge. 86 refs.