Three-dimensional Polarization Analysis Research Articles

Three-dimensional instrument polarization analysis and optimization of liquid-crystal-based Stokes polarimeter.

The Stokes polarimeter based on liquid crystal variable retarders (LCVRs) is a space polarization measurement technology widely used. However, due to the tilt of the optic axis of the LCVR with the driving voltage in the direction of light propagation and the interference in LCVR, the LCVRs-based Stokes polarimeter produces a large instrument polarization, which affects the accurate polarization measurement. In this paper, we combine polarization ray tracing with multi-beam interference, and establish a general three-dimensional polarization analysis model of the LCVRs-based Stokes polarimeter. The simulation results of adjusting the LCVR voltage to reduce the instrument polarization are analyzed, and the variation of polarization measurement accuracy with the field of view before and after optimization of the LCVRs-based Stokes polarimeter is simulated and analyzed. A LCVR structure with additional films for matching the refractive index is proposed. According to the simulation results, this structure can significantly reduce the interference effects and reduce the impact of variations in liquid crystal layer thickness on the interference effects.

Polarized neutron diffraction using a novel high-T c superconducting magnet on the single-crystal diffractometer POLI at MLZ

The polarized single-crystal diffractometer POLI is the first neutron scattering instrument routinely using 3He spin filters both to produce and to analyse neutron polarization. The instrument, with a non-magnetic goniometer, was designed to perform two types of polarized neutron diffraction experiment: spherical neutron polarimetry, also known as full three-dimensional polarization analysis in zero magnetic field, and classical polarized neutron diffraction, also called the flipping-ratio (FR) method, in high applied magnetic fields. Reported here is the implementation of the FR setup for short-wavelength neutrons on POLI using a new high-T c superconducting magnet with a maximal field of 2.2 T. The complete setup consists of a 3He polarizer, a nutator, a Mezei-type flipper, guide fields and dedicated pole pieces, together with the magnet. Each component, as well as the whole setup, was numerically simulated, optimized, built and finally successfully tested under real experimental conditions on POLI. The measured polarized neutron spin transport efficiency is about 99% at different wavelengths, e.g. as short as 0.7 Å, and up to the maximal available field of the magnet. No further depolarization of the 3He cells due to stray fields of the magnet occurs. The additional use of the available 3He analyser allows uniaxial polarization analysis experiments in fields up to 1.2 T. The results of the first experiment on the field-dependent distribution of the trigonal antiferromagnetic domains in haematite (α-Fe2O3) are presented and compared with the literature data.

Evaluation of Magnetic Field Vector by Polarization Analysis Using Pulsed Neutrons at HUNS for Magnetic Field Imaging

Magnetic field imaging using polarized pulsed neutrons is attractive technique because it has the capability to visualize spatial distribution of the magnetic field. Analyzing neutron polarization change due to neutron spin rotation result under a magnetic field at each position makes it possible to obtain a spatial distribution of magnetic field. As previous work, One-dimensional polarization analysis setup using pulsed neutrons was established at J-PARC MLF and HUNS. In this paper, we have established three-dimensional polarization analysis setup to deducea magnetic field strength and the directionprecisely and, quantitatively evaluated averaged magnetic field strength and the directioninside a coil by comparing ones calculated by magnetic calculation using FEM and one measured by a hall probe.

Double focusing Heusler monochromator and analyzer systems for the polarized neutron triple-axis spectrometer

The polarization analysis options on the thermal neutron triple-axis spectrometer TAS-1 at JRR-3 of Japan Atomic Energy Agency (JAEA) have been improved as a result of an upgrading program of the Advanced Science Research Center. In order to increase the polarized neutron intensity, we have replaced the previous flat polarizing Cu 2MnAl (Heusler) monochromator and analyzer with doubly focusing ones. Intensity gain factors of more than 30 have been achieved for 14.7 meV neutrons in measurements of incoherent neutron scattering of vanadium. Using the new monochromator and analyzer, elastic and inelastic polarized neutron scattering experiments with the conventional setup for one-dimensional polarization analysis and with CRYOPAD (Cryogenic Polarization Analysis Device) for three-dimensional polarization analysis are now routinely performed on TAS-1.

Anisotropic magnetic fluctuations in 3- [formula omitted] antiferromagnets

The anisotropy of magnetic fluctuations propagating along the high-symmetry directions in cubic systems with 3- k magnetic order is analyzed within the random-phase approximation assuming anisotropic exchange interactions. Both transverse and longitudinal structures are considered, with reference to the UO 2 and USb compounds, respectively. In the case of UO 2 , the spin-waves polarizations calculated for acoustic and optical branches are favorably compared with three-dimensional polarization analysis experiments carried out on a triple axis spectrometer. The overall spin-waves polarization behavior emerges as a consequence of the 3- k nature of the magnetic order, whatever the strength of the exchange coupling assumed.

Coupled magnetic and structural transitions in EuMn 2O 5 as studied by neutron diffraction and three-dimensional polarization analysis

A number of magnetic and structural phase transitions in EuMn 2O 5 is observed below T N ≃ 40 K by neutron diffraction on a single crystal. The magnetic structure just below T N is incommensurate with the propagation vector ( 1 2 0 0.3) . A ferroelectric transition occurs at T N with the polar displacements of Mn 3 + ions along axis a . Three-dimensional polarization analysis has shown, that magnetic moments lie in a – c plane down to T 1≃ 22 K. Second structural transition, mainly due to the polar shifts of the Mn 4 + ions along c , is observed at T 1. It is accompanied by a magnetic phase transition and by appearance of the b-component of spins.

Neutron polarization phenomena in scattering processes

The theory of polarization-dependent cross sections and of the polarization of the scattered beam in terms of the nuclear and magnetic correlation functions will be reviewed and extended. It is possible, using three-dimensional polarization analysis, to separate different correlation functions and static expectation values. Expressions which are useful for this purpose are given.

Confocal Microscope for Three-Dimensional Polarization Analysis

We present a confocal microscope for use in three-dimensional polarization analysis. Since the pinhole before the detector eliminates the light whose polarization is rotated by an imaging lens, the polarization properties of specimens are observed with high contrast. The pinhole size required to achieve high contrast is discussed. Three-dimensional resolution of the polarization microscope is also demonstrated.

Experiments with neutron polarization analysis

Abstract Neutron polarization analysis experiments of the past 25 years are reviewed. In that time the technique has progressed from a curiosity to being a useful tool to be used when needed. In early experiments, the polarization of the scattered beam was analysed in the same direction as the polarization of the incident beam but, in some later experiments, full three-dimensional polarization analysis has been employed. This article starts by writing down the interactions which the neutron has with condensed matter and deriving the cross-sections for scattering and final polarizations of the scattered beam. This is done displaying the spin state functions of the neutron explicitly. A variety of experiments is then reviewed, commencing with the elastic and inelastic scattering experiments performed by Moon, Riste and Koehler in the late 1960s. Elastic scattering experiments where it is important to separate nuclear and magnetic cross-sections such as antiferromagnetic defect scattering are reviewed together with separation out of the nuclear spin scattering for various purposes. Of particular interest are the fully three-dimensional analysis experiments which reveal more about the structure and domain populations of certain antiferromagnets. Inelastic experiments for which polarization analysis is vital are those on paramagnets at high temperatures where it is necessary to discriminate against phonon scattering. Spin glasses are treated as frozen paramagnets. Polarization analysis also has another role to play in the separation of magnetic modes in both paramagnets and ordered magnets, and several of these experiments are reviewed. Finally it is possible to tag the polarization of a neutron beam in time and space and to measure the result at another time and place and this through various techniques yields information about the change in neutron energy on scattering. The techniques of pseudo-random flipping time of flight, neutron spectral modulation and neutron spin-echo spectroscopy are briefly reviewed but the techniques of polarized-neutron-beam management are left to another review.

A possible local anomaly in the 670-km discontinuity beneath Kerguelen

The mapping of the 670-km discontinuity in regions of ascending or descending flows is of major interest for a better understanding of the nature of this discontinuity. In this paper, an attempt is made to investigate the properties of deep mantle discontinuities beneath the Kerguelen hot spot. Anomalous P to S converted waves are observed for some earthquakes recorded at the Kerguelen long-period GEOSCOPE station; the characteristics of these phases are specified owing to a three-dimensional polarization analysis of the signals. A tilted discontinuity is able to explain the data; this discontinuity dips toward the northeast with at 20°. The depth at which the conversion takes place is ∼ 880 km, assuming standard velocities in the upper mantle beneath Kerguelen, or 810 km if a hot upper mantle with a Poisson's ratio of 0.30–0.31 is present. However, the constraints given by the data are not strong enough to specify unambiguously this depth, a conversion at 600 km (or 550 km assuming a hot upper mantle) may alternatively be proposed. A strong velocity increase at the discontinuity is in each case necessary to explain the amplitude of the converted waves. Geophysical arguments show that this tilted discontinuity must be a local feature; possible other mechanisms, such as wave focusing due to undulations of the discontinuity, may also be proposed.

Combined three-dimensional polarization analysis and spin echo study of spin glass dynamics

We report direct measurements of the time-dependent spin correlation function S( k, t) for a Cu -Mn spin glass alloy over nearly 3 decades of time in a single scan in the range 10 -12 < t < 10 -9 s. This was achieved by using, for the first time, a combination of neutron spin echo and polarization analysis techniques. The results show most clearly the particular dynamics of spin glasses, namely a behaviour that can be described by a spectrum of relaxation times spreading over a wide range.

Studies on the heusler alloys - II. the structure of Cu 3Mn 2Al

The polarization analysis options on the thermal neutron triple-axis spectrometer TAS-1 at JRR-3 of Japan Atomic Energy Agency (JAEA) have been improved as a result of an upgrading program of the Advanced Science Research Center. In order to increase the polarized neutron intensity, we have replaced the previous flat polarizing Cu2MnAl (Heusler) monochromator and analyzer with doubly focusing ones. Intensity gain factors of more than 30 have been achieved for 14.7 meV neutrons in measurements of incoherent neutron scattering of vanadium. Using the new monochromator and analyzer, elastic and inelastic polarized neutron scattering experiments with the conventional setup for one-dimensional polarization analysis and with CRYOPAD (Cryogenic Polarization Analysis Device) for three-dimensional polarization analysis are now routinely performed on TAS-1.

Three-Dimensional Polarization Analysis of the Phosphorescence of Halonaphthalenes in Host Crystals

The polarization ratios b/a, b/c′, and a0/c0 of the phosphorescence emission of 2-chloro-, 2-bromo-, 2-iodo-, and 2, 3-dibromonaphthalene in biphenyl host crystal and 1-bromonaphthalene in naphthalene host crystal are determined at 77°K. The relative transition probability of the emitting oscillators along the long axis (PL), short axis (PM) and normal to the halonaphthalene molecular plane (PN) has been determined for each vibronic band in the spectrum. This is accomplished by a three-dimensional analysis, using the observed polarization ratios from any two host crystal faces and the normalization condition: PL+PM+PN=100, applied to any vibronic emission band. The relative importance of the different spin-allowed transitions in rendering the triplet—singlet spin-forbidden transition allowed is concluded from the three-dimensional analysis. In all the compounds studied, the out-of-plane electric dipole allowed transitions contribute 20%—40% of the intensity of the phosphorescence of the halonaphthalenes by direct spin—orbit perturbation [Subspectrum I:T. Pavlopoulos and M. A. El-Sayed, J. Chem. Phys. 41, 1082 (1964)]. The in-plane electric dipole allowed transitions contribute 60%—80% of the intensity via spin—orbit-vibronic perturbation (Subspectrum II). The relative amounts of the long- and short-axis polarized emissions are very sensitive to the position of the halogen atom in the naphthalene ring. The long-axis polarized emission constitutes 52%, 21%, and 39% of the total emission of the 2-halo-, 1-bromo-, and 2, 3-dibromonaphthalenes, respectively. The short-axis polarized emission constitutes 10%—20%, 36%, and 44% of the total emission of the 2-halo-, 1-bromo-, and 2, 3-dibromonaphthalenes, respectively. These observed variations in the long- and short-axis in-plane polarized emission are readily explained by the valence-bond method if the perturbing transitions involve the (intramolecular) charge-transfer (ionic) states formed from the linear combination of the ionic structures resulting from transferring electrons from the halogen atoms to the ring or to other halogens, if present. The relative amount of the out-of-plane emission is found to be largest for the 2, 3-dibromo-derivative (∼35%) in rigid glasses but lowest (∼17%) for the same compound in biphenyl host. This result shows that the decrease of the relative amount of the out-of-plane emission of 2, 3-dibromonaphthalene in biphenyl host is a result of host—guest and not bromine—bromine interaction. The fact that the different bands involving the lattice vibrations of the host are found to have polarization similar to that of the phononless band indicates that the host—guest interaction is static in nature. Two mechanisms are proposed to explain the results. In the first mechanism, the intramolecular spin—orbit coupling scheme is changed by forcing the halogen to be slightly nonplanar with the aromatic ring due to the packing forces of the host lattice. In the second mechanism, mixing between the host and guest electronic states is proposed.