1,721,007 research outputs found
Polarimetric & Spectropolarimetric Properties of FGK Type Stars and Extrasolar Systems
No full textMost of the results on extrasolar planets are obtained with Doppler surveys. Here we suggest a different approach aimed
to study the polarimetric properties of the residual interplanetary dust
Kerr-spacetime geometric optics for vortex beams
No full textWe consider the analogy between gravitational fields and optical media within the framework of geometrical optics in curved spacetime in order to describe how light can acquire orbital angular momentum (OAM) when it traverses the gravitational field of a massive rotating compact object; in particular, we analyze the interplay between OAM and polarization. Kerr spacetimes are known not only to impose a gravitational Faraday rotation on the polarization of a light beam, but also to set a characteristic fingerprint in the orbital angular momentum distribution of the radiation passing nearby a rotating black hole (BH). Kerr spacetime behaves like an inhomogeneous and anisotropic medium, in which light can acquire orbital angular momentum and spin-to-orbital angular momentum conversion can occur, acting as a polarization and phase changing medium for the gravitationally lensed light, as confirmed by the data analysis of the M87* black hole
Monitoring the late decline of the old nova RW Ursae Minoris
No full textNew 2003-2006 time-resolved photometric observations of the old nova RW UMi (1956) confirm the QPO nature of the light modulations observed. The analysis of all our historical runs show that QPOs tend to cluster around frequencies 4.96 d-1 and 12.4 d-1 while the historical superhump period remains undetected in our data. Although the two main frequencies observed might appear to be aliases of the superhump frequency 17 d-1, they should be produced by two independent mechanisms. These rather irregular QPOs might be explained by vertical oscillations of the inner regions of the accretion disk and/or by the cyclical generation in the disk of travelling density waves at the co-rotation radius of an inclined magnetic rotator. We find that the post-nova luminosity is decaying at a rate of ~0.03 mag y-1. If RW UMi is an intermediate polar system, during the decline the magnetospheric radius of the accreting white dwarf primary should increase and produce important changes in the periods of QPOs
Angular momentum properties of electromagnetic field transmitted through holey plasmonic vortex lenses
No full textWe performed three-dimensional finite elements simulations of the optical response of holey plasmonic vortex lenses, i.e., spiral grooves milled on a thin gold film with a hole at the center. We focus in particular on the properties of the wave transmitted in the underlying half-space, which is shown to be a relevant part of the transmitted field. We find out that the angular momentum selection rule for this part of the field is different from the one for the transmitted plasmonic vortex, although closely related to the plasmonic interaction of the impinging wave with the chiral geometry
Method to measure off-axis displacements based on the analysis of the intensity distribution of a vortex beam
No full textWe study the properties of the Fraunhofer diffraction patterns produced by Gaussian beams crossing spiral phase plates. We show, both analytically and numerically, that off-axis displacements of the input beam produce asymmetric diffraction patterns. The intensity profile along the direction of maximum asymmetry shows two different peaks. We find that the intensity ratio between these two peaks decreases exponentially with the off-axis displacement of the incident beam, the decay being steeper for higher strengths of the optical singularity of the spiral phase plate. We analyze how this intensity ratio can be used to measure small misalignments of the input beam with a very high precision
FrogEye, the quantum coronagraphic mask.. The photon orbital angular momentum and its applications to astronomy
No full textWe propose to realize an optical device based on the properties of photon orbital angular momentum (POAM) to detect the presence of closeby faint companions in double systems using Laguerre-Gaussian (L-G) modes of the light. We test also the possibility of using L-G modes to build coronagraph mask. We realized in the laboratory a prototype using a blazed l=1 hologram to simulate the separation between two stars, as observed with a telescope, in Laguerre-Gaussian modes
Overcoming the Rayleigh Criterion Limit with Optical Vortices
No full textWe experimentally and numerically tested the separability of two independent equally luminous monochromatic and white light sources at the diffraction limit, using optical vortices (OV). The diffraction pattern of one of the two sources crosses a fork hologram on its center generating the Laguerre-Gaussian (LG) transform of an Airy disk. The second source, crossing the fork hologram in positions different from the optical center, generates nonsymmetric LG patterns. We formulated a criterion, based on the asymmetric intensity distribution of the superposed LG patterns so created, to resolve the two sources at angular distances much below the Rayleigh criterion. Analogous experiments in white light allow angular resolutions which are still one order of magnitude below the Rayleigh criterion. The use of OVs might offer new applications for stellar separation in future space experiments
Manipulating intensity and phase distribution of composite Laguerre-Gaussian beams
No full textWe propose a method to manipulate the intensity and phase distributions of a beam with non-zero orbital angular momentum (OAM). We investigate the superposition of coherent consecutive OAM modes, with concordant topological charges values, showing that it is possible to predict and control the phase and the radial and angular dimension of the resulting beam by acting on the number of superposed modes (N) and on their minimum value of the OAM (m(min)). A general analysis from the Wigner function formalism is adopted for the geometric characterization of the beam
A TELECOMMUNICATION METHOD AND APPARATUS EXPLOITING THE TRANSMISSION AND RECEPTION OF ELECTROMAGNETIC WAVES PCT/EP2012/062004
No full textThe invention relates to a telecommunication method and apparatus for the transmission and/or reception of EM waves.
EM waves structured with a plurality of OAM modes are, said EM waves having a same carrier frequency and one or more polarization states.
One or more control signals and data signals associated to said EM waves are encodes, so that a channel for transmitting and receiving information is associated to each of said OAM modes.
Each of said control signals is associated to a corresponding OAM mode of said EM waves while each of said data signals is one-to-one associated to a corresponding OAM mode of said EM waves.
Said control signals and said data signals are simultaneously transmitted through the transmission of said EM waves and are simultaneously received through the reception of said EM waves.
Said control signals and data signals are then decoded
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