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See detailPolarised light induced birefringence in azo dye doped polymer: a new model and polarised holographic experiments
Blanche, Pierre-Alexandre ULg; Lemaire, P. C.; Maertens, Christophe et al

in Optics Communications (1997), 139(1-3), 92-98

The photoinduced birefringence of azo dye DMNPAA (2,5-dimelthyl-4-(p-nitrophenylazo)anisole) in PVK (Poly(N-vinylcarbazole)) thin film is reported. A two-layer model of the film is proposed to take into ... [more ▼]

The photoinduced birefringence of azo dye DMNPAA (2,5-dimelthyl-4-(p-nitrophenylazo)anisole) in PVK (Poly(N-vinylcarbazole)) thin film is reported. A two-layer model of the film is proposed to take into account the different results obtained in photoinduced birefringence experiments. According to this model, the sample exhibits intrinsic birefringence but the absorbed light can induce orientation of the optically active molecules contained in the first layer of the film, lending to photoinduced birefringence. Holographic experiments have been carried out in this media with recording at 514 nm and readout at 633 nm. Diffraction efficiency versus polarisation shows that these polymers can record polarisation states as well as intensity patterns. [less ▲]

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See detailA polarity reversal in the large-scale magnetic field of the rapidly rotating sun HD 190771
Petit, Pascal; Dintrans, Boris; Morgenthaler, Audrey et al

in Astronomy and Astrophysics (2009), 508

Aims. We investigate the long-term evolution of the large-scale photospheric magnetic field geometry of the solar-type star HD 190771. With fundamental parameters very close to those of the Sun except for ... [more ▼]

Aims. We investigate the long-term evolution of the large-scale photospheric magnetic field geometry of the solar-type star HD 190771. With fundamental parameters very close to those of the Sun except for a shorter rotation period of 8.8 d, HD 190771 provides us with a first insight into the specific impact of the rotation rate in the dynamo generation of magnetic fields in 1 M_sun stars. Methods: We use circularly polarized, high-resolution spectra obtained with the NARVAL spectropolarimeter (Observatoire du Pic du Midi, France) and compute cross-correlation line profiles with high signal-to-noise ratio to detect polarized Zeeman signatures. From three phase-resolved data sets collected during the summers of 2007, 2008, and 2009, we model the large-scale photospheric magnetic field of the star by means of Zeeman-Doppler imaging and follow its temporal evolution. Results: The comparison of the magnetic maps shows that a polarity reversal of the axisymmetric component of the large-scale magnetic field occurred between 2007 and 2008, this evolution being observed in both the poloidal and toroidal magnetic components. Between 2008 and 2009, another type of global evolution occured, characterized by a sharp decrease of the fraction of magnetic energy stored in the toroidal component. These changes were not accompanied by significant evolution in the total photospheric magnetic energy. Using our spectra to perform radial velocity measurements, we also detect a very low-mass stellar companion to HD 190771. [less ▲]

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See detailPolarization and Intensity Effects on the Beam-Foil-Laser Interaction
Bastin, Thierry ULg; Krastev, T.; Garnir, Henri-Pierre ULg et al

Poster (1995)

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See detailPolarization correction of the electrostatic potential for aromatic-compounds - Study of the nucleophilic-attack
Dive, Georges ULg; Dehareng, Dominique ULg

in International Journal of Quantum Chemistry (1993), 46(1), 127-136

The electrostatic potential (EP) and the polarization correction (PL) on the EP were calculated for four aromatic compounds: benzene, chlorobenzene, phenol, and benzoic amide, at the ab initio SCF level ... [more ▼]

The electrostatic potential (EP) and the polarization correction (PL) on the EP were calculated for four aromatic compounds: benzene, chlorobenzene, phenol, and benzoic amide, at the ab initio SCF level within two basis sets: 6-31G** and MINI-1. One calculation was performed using the polarized MINI-1** basis set. The quantity total interaction energy (TEH) defined as -EP + PL can be used as an indicator of the nucleophilic attack preferential position. By reference to 6-31G**, MINI-I provides very satisfactory results. Moreover, the MINI-1** results are very similar to the MINI-I ones. It appears that -EP does not provide a reliable tool to study the nucleophilic attack susceptibility, whereas TEH seems to be very well adapted for this kind of approach. [less ▲]

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See detailPolarization correction to the electrostatic potential at the CNDO and the ab initio level. Influence of the basis set expansion
Dehareng, Dominique ULg; Dive, Georges ULg; Ghuysen, Jean-Marie ULg

in Theoretica Chimica Acta (1991), 79(2), 141-152

The influence of the basis set on the electrostatic potential corrected for polarization has been studied for H2S, CH3SH and COHCH2SH. The position and deepness of the minima and the height of the barrier ... [more ▼]

The influence of the basis set on the electrostatic potential corrected for polarization has been studied for H2S, CH3SH and COHCH2SH. The position and deepness of the minima and the height of the barrier between symmetric minima is discussed at both the deorthogonalized CNDO/2 and ab initio levels within STO-3G, 3-21G, 4-31G, 6-31G and 6-311G basis sets. The calculation of the electrostatic potential and corrected one using CNDO deorthogonalized coefficients including 3d orbitals has been applied at the first time on sulfur-containing molecules. The influence of polarization and diffuse functions has also been analysed and the incidence of the polarization correction on the relative proton affinity in NH2(CH2)3NHCH3 and in the adenine molecule has been investigated at the CNDO and ab initio levels. At both levels, the relative proton affinity of several basic sites in the same molecule can be qualitatively expressed without inclusion of the polarization correction except in the case of substituted amines. [less ▲]

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See detailPolarization dependence of the exchange energy
Gonze, X.; Ghosez, Philippe ULg; Godby, R. W.

in Physical Review Letters (1997), 78(10), 2029-2029

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See detailThe Polarization Evolution of the Optical Afterglow of GRB 030329
Greiner, J.; Klose, S.; Reinsch, K. et al

in GAMMA-RAY BURSTS: 30 YEARS OF DISCOVERY (2004, September 01)

We report 31 polarimetric observations of the afterglow of GRB 030329 with high signal-to-noise and high sampling frequency. The data imply that the afterglow magnetic field has small coherence length and ... [more ▼]

We report 31 polarimetric observations of the afterglow of GRB 030329 with high signal-to-noise and high sampling frequency. The data imply that the afterglow magnetic field has small coherence length and is mostly random, probably generated by turbulence. [less ▲]

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See detailPolarization holography for vortex retarders recording
Piron, Pierre ULg; Blain, Pascal ULg; Mawet, Dimitri et al

in Applied Optics (2013), 52(28), 7040-7048

We present an original static recording method for vortex retarders (VRs) made from liquid crystal polymers (LCPs) using the superimposition of several polarized beams. VRs are birefringent plates ... [more ▼]

We present an original static recording method for vortex retarders (VRs) made from liquid crystal polymers (LCPs) using the superimposition of several polarized beams. VRs are birefringent plates characterized by a rotation of their fast axis about their center. The new method is based on polarization holography and photo-orientable LCP. Combining several polarized beams induces the polarization patterns required for the recording process of VRs without mechanical action. A mathematical description of the method, the outcomes of the numerical simulations, and the first experimental results are presented. [less ▲]

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See detailPolarization holography reveals the nature of the grating in polymers containing azo-dye
Blanche, Pierre-Alexandre ULg; Lemaire, P. C.; Maertens, Christophe et al

in Optics Communications (2000), 185(1-3), 1-12

To study the origin of reversible holographic recording in three polymers containing the same azo-dye, we have measured the diffraction efficiency and analyzed the gratings characteristics for various ... [more ▼]

To study the origin of reversible holographic recording in three polymers containing the same azo-dye, we have measured the diffraction efficiency and analyzed the gratings characteristics for various writing beams polarizations. The amplitude of the holographic grating, as well as the ratio between index and absorption modulations, have been investigated by gratings shifting. The total amount of diffracted power and the diffraction efficiency versus the reading beam polarization has been measured by non-degenerated four waves mixing. These experiments have revealed that the molecular mechanisms of holographic recording in the studied compounds are different. The photoinduced orientation of the chromophores is predominant for C6-C11-DMNPAA; so, in C11-C6-DMNPAA (DMNPAA: 2,5-dimethyl-4-(p-nitrophenylazo)anisole), the refractive index variation comes from the presence of both trans and cis populations generated by photoisomerization. The behavior of the PVK:DMNPAA is included between these extreme cases since both phenomena act. [less ▲]

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See detailPolarization Holography with liquid crystals polymers and applications
Piron, Pierre ULg; Blain, Pascal ULg; Habraken, Serge ULg et al

in International Conference on Fibre Optics and Photonics (2012, December)

Liquid Crystals Polymers are birefringent molecules locally orientable. By recording the polarization pattern due to the overlap of differently polarized beams on LCP, space-variant retarders are realized ... [more ▼]

Liquid Crystals Polymers are birefringent molecules locally orientable. By recording the polarization pattern due to the overlap of differently polarized beams on LCP, space-variant retarders are realized. We present two applications polarization holography and coronagraphy. [less ▲]

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See detailPolarization Holography with liquid crystals polymers and applications
Piron, Pierre ULg; Blain, Pascal ULg; Habraken, Serge ULg et al

Conference (2012, December 10)

Liquid Crystals Polymers are birefringent molecules locally orientable. By recording the polarization pattern due to the overlap of differently polarized beams on LCP, space-variant retarders are realized ... [more ▼]

Liquid Crystals Polymers are birefringent molecules locally orientable. By recording the polarization pattern due to the overlap of differently polarized beams on LCP, space-variant retarders are realized. We present two applications polarization holography and coronagraphy [less ▲]

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See detailPolarization in BAL QSOs (Lamy+, 2004)
Lamy, H.; Hutsemekers, Damien ULg

Textual, factual or bibliographical database (2004)

Table 1 contains optical properties of 139 BAL QSOs. It is essentially a compilation of 93 BAL QSOs coming from large polarization surveys. In addition, we also consider 46 BAL QSOs with good quality ... [more ▼]

Table 1 contains optical properties of 139 BAL QSOs. It is essentially a compilation of 93 BAL QSOs coming from large polarization surveys. In addition, we also consider 46 BAL QSOs with good quality optical (UV rest-frame) spectra but no polarization data. (1 data file). [less ▲]

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See detailPolarization measurement with space-variant retarders in liquid crystal polymers
Piron, Pierre ULg; Blain, Pascal ULg; Habraken, Serge ULg

in SPIE proceedings 8160, SPIE Optics +Photonics 2011 San Diego (2011)

We present a real-time polarization measurement method with a space-variant phase retarder in liquid crystal polymers. This retarder presents a continuous and periodical variation of its optical axis ... [more ▼]

We present a real-time polarization measurement method with a space-variant phase retarder in liquid crystal polymers. This retarder presents a continuous and periodical variation of its optical axis orientation. The method computes the Stokes parameters of an incident beam by studying the intensity distribution after the retarder and a linear polarizer. This paper contains the mathematical modelization, the numerical simulation, the description of the experimental setup, the results for several completely polarized beams and the future developments of this method. [less ▲]

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See detailPolarization properties of a sample of broad absorption line and gravitationally lensed quasars
Hutsemekers, Damien ULg; Lamy, H.; Remy, M.

in Astronomy and Astrophysics (1998), 340

New broad-band linear polarization measurements have been obtained for a sample of 42 optically selected QSOs including 29 broad absorption line (BAL) QSOs. The polarization properties of different sub ... [more ▼]

New broad-band linear polarization measurements have been obtained for a sample of 42 optically selected QSOs including 29 broad absorption line (BAL) QSOs. The polarization properties of different sub-classes have been compared, and possible correlations with various spectral indices searched for. The main results of our study are: (1) Nearly all highly polarized QSOs of our sample belong to the sub-class of BAL QSOs with low-ionization absorption features (LIBAL QSOs). (2) The range of polarization is significantly larger for LIBAL QSOs than for high-ionization (HI) BAL QSOs and non-BAL QSOs. (3) There is some indication that HIBAL QSOs as a class may be more polarized than non-BAL QSOs and therefore intermediate between LIBAL and non-BAL QSOs, but the statistics are not compelling from the sample surveyed thus far. (4) For LIBAL QSOs, the continuum polarization appears significantly correlated with the line profile detachment index, in the sense that LIBAL QSOs with P Cygni-type profiles are more polarized. No correlation was found with the strength of the low- or the high-ionization absorption features, nor with the strength or the width of the emission lines. These results are consistent with a scenario in which LIBAL QSOs constitute a different class of radio-quiet QSOs with more absorbing material and more dust. Higher maximum polarization can therefore be reached, while the actually measured polarization depends on the geometry and orientation of the system as do the line profiles. The observed correlation is interpreted within the framework of recent ``wind-from-disk'' models. Tables~2 and 3 are also available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html}\fnmsep\thanks{Based on observations collected at the European Southern Observatory (ESO, La Silla) [less ▲]

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See detailPolarization properties of broad absorption line QSOs: New statistical clues
Lamy, H.; Hutsemekers, Damien ULg

in Astronomy and Astrophysics (2004), 427

We report the results of several statistical tests performed on a large sample of 139 broad absorption line (BAL) QSOs with good quality optical spectra and/or optical polarization data. Correlations ... [more ▼]

We report the results of several statistical tests performed on a large sample of 139 broad absorption line (BAL) QSOs with good quality optical spectra and/or optical polarization data. Correlations between ten optical indices and the polarization degree p[SUB]0[/SUB] are systematically searched for. We find six significant non-trivial correlations. In order to identify the most important correlations, we perform a principal component analysis with a sample of 30 BAL QSOs and eight quantities (including p[SUB]0[/SUB]). Most of the variance (Ë 57%) in the data is contained in two principal components called PC1 and PC2. PC1 is mainly dominated by the correlation between the balnicity index BI and the strength of the Fe II emission; it may be driven by the accretion rate of matter onto the central compact object. The variance in PC2 is essentially due to the anti-correlation between p[SUB]0[/SUB] and the detachment index DI, indicating that BAL QSOs with P Cygni profiles (DIâ ª) are usually more polarized than those objects with C IV absorption troughs well detached from the corresponding emission lines (DIâ «). We show that PC2 may be related to the orientation of the BAL QSOs with respect to the line of sight. We also present new spectropolarimetric observations of six BAL QSOs. By adding spectropolarimetric data from the literature, we build a sample of 21 BAL QSOs for which we define four spectropolarimetric indices describing the polarization properties of the absorption and emission lines. We find that the polarization of the C III]] emission line is systematically higher than the polarization of the C IV emission line, and that the highest polarization in the troughs is correlated to the balnicity index. Another important result emerging from the statistical tests performed on this spectropolarimetric sample is a possible anti-correlation between the detachment index and a quantity SI which measures the ratio of the depths of the C IV absorption in the polarized flux and in the total flux. This correlation indicates that in BAL QSOs with P cygni profiles, the BAL troughs in the polarized flux are nearly as deep as in the total flux while, in BAL QSOs with detached absorptions, the BAL troughs in the polarized flux are much weaker than in the total flux. We show that our main results may be explained in the framework of a ``two-component'' wind model which is a natural extension of the classical wind-from-disk models. In this model, the broad absorption occurs in a dense equatorial wind emerging from the accretion disk, while scattering and polarization mainly take place in a polar region. The orientation relative to the observer drives the correlations p[SUB]0[/SUB] - DI and DI - SI. While most of our observations can be explained within this framework, there are also several indications that other polarization mechanisms, and more particularly resonance scattering, may also be at work. Based on observations collected at the European Southern Observatory (ESO, La Silla). Table 1 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http: / / cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/427/107 [less ▲]

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See detailThe Polarization Properties of Broad Absorption Line QSOs: Observational Results
Hutsemekers, Damien ULg; Lamy, H.

in Mass Outflow in Active Galactic Nuclei: New Perspectives. ASPC 255 (2002)

Correlations between BAL QSO intrinsic properties and polarization have been searched for. Some results are summarized here, providing possible constraints on BAL outflow models.

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See detailPolarization radiation of vortex electrons with large orbital angular momentum
Ivanov, Igor ULg; Karlovets, Dmitry

in Physical Review. A (2013), 88(4), 043840

Vortex electrons—freely propagating electrons whose wave functions have helical wave fronts—could become a novel tool in the physics of electromagnetic radiation. They carry a nonzero intrinsic orbital ... [more ▼]

Vortex electrons—freely propagating electrons whose wave functions have helical wave fronts—could become a novel tool in the physics of electromagnetic radiation. They carry a nonzero intrinsic orbital angular momentum (OAM) ℓ with respect to the propagation axis and, for ℓ≫1, a large OAM-induced magnetic moment μ≈ℓμB (μB is the Bohr magneton), which influences the radiation of electromagnetic waves. Here, we consider in detail the OAM-induced effects caused by such electrons in two forms of polarization radiation, namely, in Cherenkov radiation and transition radiation. Thanks to the large ℓ, we can neglect quantum or spin-induced effects, which are of the order of ℏω/Ee≪1, but retain the magnetic moment contribution ℓℏω/Ee≲1, which makes the quasiclassical approach to polarization radiation applicable. We discuss the magnetic moment contribution to polarization radiation, which has never been experimentally observed, and study how its visibility depends on the kinematical parameters and the medium permittivity. In particular, it is shown that this contribution can, in principle, be detected in azimuthally nonsymmetrical problems, for example when vortex electrons obliquely cross a metallic screen (transition radiation) or move near it (diffraction radiation). We predict a left-right angular asymmetry of the transition radiation (in the plane where the charge radiation distributions would stay symmetric), which appears due to an effective interference between the charge radiation field and the magnetic moment contribution. Numerical values of this asymmetry for vortex electrons with Ee=300 keV and ℓ=100–1000 are 0.1%–1%, and we argue that this effect could be detected with existing technology. The finite conductivity of the target and frequency dispersion play crucial roles in these predictions. [less ▲]

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See detailPolarization vortices in germanium telluride nanoplatelets: A theoretical study
Durgun, Engin ULg; Ghosez, Philippe ULg; Shaltaf, R. et al

in Physical Review Letters (2009), 103

Using first-principles calculations based on density functional theory, we study the properties of germanium telluride crystalline nanoplatelets and nanoparticles. Above a diameter of 2.7 nm, we predict ... [more ▼]

Using first-principles calculations based on density functional theory, we study the properties of germanium telluride crystalline nanoplatelets and nanoparticles. Above a diameter of 2.7 nm, we predict the appearance of polarization vortices giving rise to an unusual ferrotoroidic ground state with a spontaneous and reversible toroidal moment of polarization. We highlight the crucial role of inhomogeneous strain in stabilizing polarization vortices. Combined with the phase-change properties of germanium telluride, the ferrotoroidic properties could be of practical interest for ternary logic applications. [less ▲]

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See detailPolarization-corrected electrostatic potentials of aromatic compounds
Dehareng, Dominique ULg; Dive, Georges ULg; Ghuysen, Jean-Marie ULg

in Journal of the American Chemical Society (1993), 115(15), 6877-6882

The electrostatic potentials (EPS) corrected for polarization (TPS) of the aromatic compounds benzene, aniline, chlorobenzene, nitrobenzene, phenol, benzamide, and N-phenylacetamide have been calculated ... [more ▼]

The electrostatic potentials (EPS) corrected for polarization (TPS) of the aromatic compounds benzene, aniline, chlorobenzene, nitrobenzene, phenol, benzamide, and N-phenylacetamide have been calculated at the ab initio SCF level within three basis sets: 6-31G**, MINI-1, and STO-3G. For chlorobenzene in its MINI-1-optimized geometry, the calculation was also performed within MINI-1**. By reference to 6-31G**, the MINI-1-computed EP is much more satisfactory than the STO-3G-computed EP, whereas the MINI-I and STO-3G basis sets give very similar total potentials corrected for polarization (TPs). The MINI-1** basis set appears to be miscalibrated for computing EPs. It provides qualitative results that differ from those obtained with the 6-31G** basis set. The EP has a negative well above the middle of the benzene ring, while the TP exhibits a negative crown just above the benzene carbon atoms, where electrophilic attack takes place. The TP calculated for the interaction of nitrobenzene with a hydride ion instead of a proton allowed analyzation of the effects of polarization on the positive EP above the N-C bond. [less ▲]

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