Search results for "polarization."
showing 10 items of 1842 documents
Wannier90 as a community code: new features and applications
2019
Wannier90 is an open-source computer program for calculating maximally-localised Wannier functions (MLWFs) from a set of Bloch states. It is interfaced to many widely used electronic-structure codes thanks to its independence from the basis sets representing these Bloch states. In the past few years the development of Wannier90 has transitioned to a community-driven model; this has resulted in a number of new developments that have been recently released in Wannier90 v3.0. In this article we describe these new functionalities, that include the implementation of new features for wannierisation and disentanglement (symmetry-adapted Wannier functions, selectively-localised Wannier functions, s…
Variability and polarization in the inner jet of 3C 395
2001
We present new results on the parsec-scale jet of the quasar 3C395, derived from VLBI polarization sensitive observations made in 1995.91 and 1998.50 at 8.4, 15.4 and 22.2 GHz. The observations show a complex one-sided jet extending up to 20 mas, with a projected magnetic field essentially aligned with the radio jet. The emission is strongly dominated, in total intensity and polarization, by the core and the inner jet region (of ~3 mas length). We have studied the details of this dominant region finding clear structural variations during this ~2.5 years period, in contrast with the apparent quietness of the jet structure inferred from lower resolution VLBI observations. We observe the eject…
Higher-order polarizations on the Virasoro group and anomalies
1991
In a previous paper the authors showed that the space of (first order) polarized functions on the Virasoro group is not, in general, irreducible. The full reduction was explicitly achieved by taking the orbit of the enveloping algebra through the vacuum. This additional step provided the proper quantization in the “strong-coupling” domain 0<c≦1. In this paper we introduce the concept of “higher order polarization” as a generalization of that of polarization. We prove that the imposing of the additional (higher-order) polarization conditions is equivalent to the taking of the above-mentioned orbit. This demonstrates that the generalized (higher-order) polarization conditions suffice to obtai…
Field-free two-direction alignment alternation of linear molecules by elliptic laser pulses
2005
We show that a linear molecule subjected to a short specific elliptically polarized laser field yields postpulse revivals exhibiting alignment alternatively located along the orthogonal axis and the major axis of the ellipse. The effect is experimentally demonstrated by measuring the optical Kerr effect along two different axes. The conditions ensuring an optimal field-free alternation of high alignments along both directions are derived.
Measurement of high order Kerr refractive index of major air components
2009
International audience; We measure the instantaneous electronic nonlinear refractive index of N2 , O2 , and Ar at room temperature for a 90 fs and 800 nm laser pulse. Measurements are calibrated by post-pulse molecular alignment through a polarization technique. At low intensity, quadratic coefficients n2 are determined. At higher intensities, a strong negative contribution with a higher nonlinearity appears, which leads to an overall negative nonlinear Kerr refractive index in air above 26 TW/cm2 .
Theory of spontaneous polarization and birefringence in the tetragonal phase of KNbO3
1995
Abstract The microscopic mechanism of optical anisotropy in the tetragonal phase of KNbO3 is discussed taking account of the dipole-dipole effect due to the ionic and electronic polarizations of the crystal and the spontaneous Kerr effect. The last effect is a cause of the strong local field acting on the constituent ions. For the spontaneous polarization we use only the first effect. It is found that the birefringence and the spontaneous polarization are in good agreement with the experimental data.
Measurement of high order Kerr refractive index of major air components: erratum
2010
A clarification is missing concerning the high order Kerr non-linearities deduced from our experimental data published in [Opt. Express 17, 13429-13434 (2009)]. Here, we rectify this omission by making explicit the distinction between cross-Kerr and Kerr effects, and by extrapolating the value of the nonlinear refractive index for the last effect. Since the occurrence of sign inversion in the Kerr effect is not affected, the overall report in [Opt. Express 17, 13429-13434] remains valid.
Predicting the structure and vibrational frequencies of ethylene using harmonic and anharmonic approaches at the Kohn–Sham complete basis set limit
2016
In this work, regular convergence patterns of the structural, harmonic, and VPT2-calculated anharmonic vibrational parameters of ethylene towards the Kohn–Sham complete basis set (KS CBS) limit are demonstrated for the first time. The performance of the VPT2 scheme implemented using density functional theory (DFT-BLYP and DFT-B3LYP) in combination with two Pople basis sets (6-311++G** and 6-311++G(3df,2pd)), the polarization-consistent basis sets pc-n, aug-pc-n, and pcseg-n (n = 0, 1, 2, 3, 4), and the correlation-consistent basis sets cc-pVXZ and aug-cc-pVXZ (X = D, T, Q, 5, 6) was tested. The BLYP-calculated harmonic frequencies were found to be markedly closer than the B3LYP-calculated h…
Measurement of the mixing-induced and CP-violating parameters of Bs -> phi gamma decays at LHCb
2018
En esta tesis se presenta la primera medida de los observables de violación de CP e inducidos por mezcla de la desintegración Bs -> phi gamma (los observables A, S y C), que aparecen en la fracción de desintegración en función del tiempo. Se han utilizado los datos tomados por el experimento LHCb durante los años 2011 y 2012, representando una luminosidad integrada de 3 fb-1 en total. El Modelo Estándar de física de partículas describe las propiedades de todas las partículas elementales y de las interacciones fuerte, débil y electromagnética. A pesar de su gran éxito predictivo, resulta necesaria una extensión del mismo puesto que no explica determinados fenómenos que han sido observados en…
Search for radiative b-baryon decays and study of their anomalous photon polarization at LHCb
2022
En esta tesis se presenta el estudio de dos desintegraciones radiativas de bariones que contienen un quark bottom: Lambda_b -> Lambda gamma and Xi_b^- -> Xi^- gamma. En primer lugar, se ha realizado una búsqueda de dichas desintegraciones usando datos tomados por el experimento LHCb para medir sus fracciones de desintegración. En segundo lugar, se usan los candidatos señal para medir la polarización del fotón a haciendo uso del formalismo de helicidad. Esta tesis presenta la primera medida de la polarización del fotón usando la desintegración radiativa b-bariónica Lambda_b -> Lambda gamma, y el primer estudio de la desintegración Xi_b^- -> Xi^- gamma. El marco teórico actual de la física de…