共查询到20条相似文献,搜索用时 15 毫秒
1.
Ch. V. Felde A. A. Chernyshov G. V. Bogatyryova P. V. Polyanskii M. S. Soskin 《JETP Letters》2008,88(7):418-422
Vector singularities are predicted and discovered experimentally in partially polarized combined fields formed by incoherent superposition of orthogonally polarized beams. Such singularities are U contours with zero degree of polarization and isolated P points with unit degree of polarization centered at vortices of the orthogonally polarized component of the combined beam. Crossing a U contour switches the polarization state to the orthogonal one. The above-mentioned singularities are adequately described in terms of the complex degree of polarization in the Stokes-space representation. It is shown that the field elements corresponding to the extrema of the complex degree of polarization form the vector skeleton of a partially coherent nonuniformly polarized field. 相似文献
2.
The 3D structure of randomly polarized light fields is exemplified by its polarization singularities: lines along which the polarization is purely circular (C lines) and surfaces on which the polarization is linear (L surfaces). We visualize these polarization singularities experimentally in vector laser speckle fields, and in numerical simulations of random wave superpositions. Our results confirm previous analytical predictions [M. R. Dennis, Opt. Commun. 213, 201 (2002)] regarding the statistical distribution of types of C points and relate their 2D properties to their 3D structure. 相似文献
3.
The composite Stokes singularities formed in the coherent and incoherent superposition of two vector monochromatic coherent optical fields are studied and compared analytically and numerically. It is shown that the dynamic behavior of composite Stokes singularities depends on the superposition scheme (coherent or incoherent superposition), initial spatial distributions of the two superimposed fields, and propagation distance, and for the coherent superposition additionally depends on the relative phase of the two fields. There exist S12 (C-points), S31, S23 composite singularities, and L-lines, in particular, V-points and C-lines at the transverse plane. Generally, both V-points and C-lines are unstable. For the coherent superposition the degree of polarization P=1, whereas for the incoherent superposition P may be less than 1 and is variable upon propagation. The results are illustrated analytically and numerically. 相似文献
4.
The analytical expression for nonparaxial Gaussian vortex beams propagating in free space is derived, which enables us to study phase and polarization singularities in nonparaxial vector wavefields. Differing from the polarization singularities formed by two transverse electric-field components in the paraxial regime, the polarization singularities can be formed by the transverse and longitudinal electric-field components of nonparaxial beams, and there exist C-points and L-lines. The variation of the beam parameters and propagation distance will result in a shift of phase and polarization singularities, but their position relation remains unchanged and the topological relationship holds true. 相似文献
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The geometry of distributions of the polarization of light in conoscopic patterns of planar oriented nematic and cholesteric
liquid crystal (LC) cells is described in terms of the polarization singularities including C-points (points of circular polarization) and L lines (lines of linear polarization). Conditions for the formation of polarization singularities (C-points) in an ensemble of conoscopic patterns parametrized by the polarization azimuth and ellipticity of the incident light
wave have been studied. A characteristic feature of these conditions is selectivity with respect to the polarization parameters
of the incident light wave. The polarization azimuth and ellipticity are determining parameters for nematic and cholesteric
LC cells, respectively. 相似文献
7.
Derry W. Jones 《Contemporary Physics》2013,54(4):387-389
A beam of electrons may have the spins of the individual electrons preferentially polarized in a specified direction. The resulting state of polarization of the electron beam is described by a polarization vector p. This polarization vector is affected in direction and magnitude by macroscopic electric and magnetic fields. The relevance of this to precise measurement of the electronic g-factor, end to the problems of handling polarized beams (as in accelerating systems), is discussed. Some spinsensitive interactions, and various methods of producing intense highly polarized electron beams, are described. In a final paragreph an outline is given of the mathematical formalism used in describing polarization phenomene. 相似文献
8.
The propagation-dependent polarization vector fields are experimentally created from an isotropic microchip laser with a longitudinal-transverse coupling and entanglement of the polarization states. The experimental three-dimensional coherent vector fields are analytically reconstructed with a coherent superposition of orthogonal circularly polarized vortex modes. Each polarized component is found to comprise two Laguerre-Gaussian modes with different topological charges. With the analytical representation, the polarization singularities, on which the electric polarization ellipse is purely circular (C lines) or purely linear (L surfaces), are explored. The C line singularities are found to form an intriguing hyperboloidal structure. 相似文献
9.
V. V. Ponevchinsky A. I. Goncharuk V. I. Vasil’ev N. I. Lebovka M. S. Soskin 《JETP Letters》2010,91(5):241-244
The structural features, as well as the optical and electrophysical properties of a 5CB nematic liquid crystal with additions
of multilayer carbon nanotubes, have been investigated in the concentration range C = 0.0025–0.1 wt %. The self-aggregation of nanotubes into clusters with a fractal structure occurs in the liquid crystal.
At 0.025 wt %, the clusters are merged, initiating the percolation transition of the composite to a state with a high electric
conductivity. The strong interaction of 5CB molecules with the surface of nanotube clusters is responsible for the formation
of micron surface liquid crystal layers with an irregular field of elastic stresses and a complex structure of birefringence.
They are easily observed in a polarization microscope and visualize directly invisible submicron nanotube aggregates. Their
transverse size increases when an electric field is applied to the liquid crystal cell. Two mechanisms of the generation of
optical singularities in the passing laser beam have been revealed. Optical vortices appear in the speckle fields of laser
radiation scattered at the indented boundaries of the nanotube clusters, whereas the birefringence of the beam in surface
liquid-crystal layers is accompanied by the appearance of polarization C points. 相似文献
10.
Polarization singularities,which emerge from the incoherent superposition of two vector electric fields with the same frequency,and their evolution in free space are studied analytically and illustrated by numerical examples.It is shown that there exist C-points,L-lines,in particular,C-lines in incoherently superimposed two-dimensional wavefields.Usually,the C-lines are unstable and disappear during the free-space propagation.The motion,pair creation-annihilation process of the emergent C-points,as well as the distortion of the L-lines may take place,and the degree of polarization of the emergent C-points varies upon propagation and may be less than 1. 相似文献
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Freund I 《Optics letters》2003,28(22):2150-2152
Elliptical polarization can appear in only monochromatic optical fields. In polychromatic vector fields the polarization is a Lissajous figure, but in only commensurate fields do the figures have well-defined shapes; in other fields the shapes are undefined. Nonetheless, I show that a given paraxial polychromatic vector field has a coherency ellipse field associated with it that contains polarization singularities and stationary points that are surrogates for the corresponding critical points of the parent optical field. 相似文献
13.
W. Drechsler 《General Relativity and Gravitation》1983,15(8):703-723
A generalized theory of gravitation is discussed which is based on a Riemann-Cartan space-time,U 4, with an axial vector torsion field. Besides Einstein's equations determining the metric of theU 4, a system of nonlinear field equations is established coupling an axial vector source current to the axial vector torsion field. The properties of the solutions of these equations are discussed assuming a London-type condition relating the axial current and torsion field. To characterize the solutions use is made of the Euler and Pontrjagin forms and the associated quadratic curvature invariants for theU 4 space-time. It is found that there exists for a Riemann-Cartan space-time a relation between the zeros of the axial vector torsion field and the singularities of the Pontrjagin invariant, which is analogous to the well-known Hopf relation between the zeros of vector fields and the Euler characteristic. 相似文献
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Taking the partially coherent cosh-Gaussian (ChG) vortex beam as an illustrative example, the composite spectral Stokes singularities formed by coherent and incoherent superpositions of partially coherent vortex beams beyond the paraxial approximation are studied, where the effect of superposition scheme on composite spectral Stokes singularities is stressed. It is shown that there exist s12 (C-points), s23 and s31 composite spectral Stokes singularities, which are variable by varying a control parameter, such as the spatial correlation length, waist width, off-axis distance, or decentered parameter, as well as the propagation distance. In particular, the number, position, degree of polarization of composite spectral Stokes singularities and the critical point at which the creation–annihilation process takes place depend on the superposition scheme. A comparison with the previous work is also made. 相似文献
16.
We analyze Young’s interference experiment for the case that two correlated, linearly polarized beams are used. It is shown that even when the incident fields are partially coherent, there are always correlation singularities (pairs of lines where the fields are completely uncorrelated) on the observation screen. These correlation singularities evolve in a non-trivial manner into dark lines (phase singularities in the paraxial approximation). The latter in turn each unfold into a triplet of polarization singularities, namely an L-line and two C-lines of opposite handedness. 相似文献
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Speckle patterns produced by random optical fields with two (or more) widely different correlation lengths exhibit speckle spots that are themselves highly speckled. Using computer simulations and analytic theory we present results for the point singularities of speckled speckle fields, namely, optical vortices in scalar (one polarization component) fields and C points in vector (two polarization components) fields. In single correlation length fields both types of singularities tend to be more or less uniformly distributed. In contrast, the singularity structure of speckled speckle is anomalous; for some sets of source parameters vortices and C points tend to form widely separated giant clusters, for other parameter sets these singularities tend to form chains that surround large empty regions. The critical point statistics of speckled speckle is also anomalous. In scalar (vector) single correlation length fields phase (azimuthal) extrema are always outnumbered by vortices (C points). In contrast, in speckled speckle fields, phase extrema can outnumber vortices and azimuthal extrema can outnumber C points by factors that can easily exceed 10(4) for experimentally realistic source parameters. 相似文献
20.
Luyou Xie Simei Lu Xiaoshu Cheng Denghong Zhang Jun Jiang Chenzhong Dong 《X射线光谱测定》2019,48(6):657-663
K-shell dielectronic, trielectronic, and quadruelectronic recombination and polarization of X-ray emission have been studied for the highly charged Si9+ ions in the initial ground state 2P1/2 and the metastable state 2P3/2 using the Flexible Atomic Code. It is found that the resonant recombination cross section from the long-lived metastable state is comparable in magnitude with that of the ground state, so it is important for plasma diagnostics. For Si9+(2P1/2), trielectronic recombination contributions of nearly 25% to the total resonant recombination strength are predicted, which is less than previous calculations. We compare the degree of linear polarization for the eleven dominant resonant recombination satellite lines from the initial parent Si9+(2P1/2) and Si9+(2P3/2) ions. For the same X-ray lines, large variations of polarization are found between 2P1/2 and 2P3/2, which can be employed to diagnose formation mechanisms of intermediate resonance states and corresponding X-ray lines. 相似文献