arXiv subjects

F. Tamburini

Publications and source records attributed to F. Tamburini.

27 records · Page 2Linked to original sources

arXiv2008

Optical vortices with starlight: Implications for ground-based stellar coronagraphy

Using an l = 1 blazed fork-hologram at the focal plane of the Asiago 122 cm telescope, we obtained optical vortices from the stellar system Rasalgethi (alpha Herculis) and from the single star Arcturus (alpha Bootis). We have analyzed the structure of the optical vortices obtained from non-monochromatic starlight under very poor seeing conditions using a fast CCD camera to obtain speckle patterns and carry out the lucky imaging technique, alternative to adaptive optics. With the insertion of a red filter and of a Lyot stop we performed l = 1 optical vortex coronography the double star HD74010. The results are in agreement with theory and numerical simulations. Our results open the way to applications of optical vortices to ground based astronomical observations, in particular for coronagraphy with l > 1 masks. No intrinsic orbital angular momentum was detected in the starlight.

physics.optics↗

arXiv2006

Overcoming the Rayleigh Criterion Limit with Optical Vortices

We experimentally and numerically tested the separability of two independent equally-luminous monochromatic and white light sources at the diffraction limit, using Optical Vortices (OV), related to the Orbital Angular Momentum (OAM) of light. The diffraction pattern of one of the two sources crosses a phase modifying device (fork-hologram) on its center generating the Laguerre-Gaussian (L-G) transform of an Airy disk. The second source, crossing the fork-hologram in positions different from the optical center, acquires different OAM values and generates non-symmetric L-G patterns. We formulated a criterion, based on the asymmetric intensity distribution of the superposed L-G patterns so created, to resolve the two sources at angular distances much below the Rayleigh criterion. Analogous experiments carried out in white light allow angular resolutions which are still one order of magnitude below the Rayleigh criterion. The use OVs might offer new applications for stellar separation in future space experiments.

astro-ph↗

arXiv2006

Do magnetic fields contribute to the dynamical stability of the secondaries of CVs against mass transfer?

We show the presence of CVs with orbital periods in the range 3.5-7 h and mass ratios q=M2/M1 above the critical values for dynamically stable mass transfer. We explore whether the magnetic fields produced in the secondaries alter the theoretical mass ratio limits allowing dynamical stability. Since magnetic fields change the specific heats and the polytropic exponent gamma of the gas in the convective envelope, the mass-radius adiabatic exponent xi_ad also changes. We find that turbulent magnetic fields can produce 10% less restrictive critical q-profiles while large-scale toroidal and poloidal fields have smaller effects. Thus, magnetic fields alone do not account for the stability of all the anomalous CVs. However, we found that the small variations of xi_ad induced by solar-type magnetic cycles explain the amplitudes of the cyclic accretion luminosity variations shown by several CVs.

astro-ph↗

arXiv2005

QuantEYE: The Quantum Optics Instrument for OWL

QuantEYE is designed to be the highest time-resolution instrument on ESO:s planned Overwhelmingly Large Telescope, devised to explore astrophysical variability on microsecond and nanosecond scales, down to the quantum-optical limit. Expected phenomena include instabilities of photon-gas bubbles in accretion flows, p-mode oscillations in neutron stars, and quantum-optical photon bunching in time. Precise timescales are both variable and unknown, and studies must be of photon-stream statistics, e.g., their power spectra or autocorrelations. Such functions increase with the square of the intensity, implying an enormously increased sensitivity at the largest telescopes. QuantEYE covers the optical, and its design involves an array of photon-counting avalanche-diode detectors, each viewing one segment of the OWL entrance pupil. QuantEYE will work already with a partially filled OWL main mirror, and also without [full] adaptive optics.

astro-ph↗

arXiv2005

FrogEye, the Quantum Coronagraphic mask. The Photon Orbital Angular Momentum and its applications to Astronomy

We 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.

astro-ph↗

arXiv2004

Space-to-ground quantum-communication using an optical ground station: a feasibility study

We have tested the experimental prerequisites for a Space-to-Ground quantum communication link between satellites and an optical ground station. The feasibility of our ideas is being assessed using the facilities of the ASI Matera Laser Ranging Observatory (MLRO). Specific emphasis is put on the necessary technological modifications of the existing infrastructure to achieve single photon reception from an orbiting satellite.

quant-ph↗

arXiv2002

Polarization statistics of extra-solar systems

We have analysed the optical polarimetric properties of nearby intermediate-late type MS stars and examined in some detail the pecularities displayed by those known to have planets. We find that: i) the polarization degree is not strictly correlated with the presence of planets; ii) there is a lack of high eccentricity planets at high optical linear polarization levels; iii) no clear correlation is seen between metallicity and polarization amongst extra-solar systems; iv) the contribution to the polarization by the interstellar medium seems to become effective only after ~70 pc.

astro-ph↗

arXiv2001

Is the old nova RW UMi (1956) an intermediate polar?

From photometric observations of the old nova RW UMi (1956) we have discovered the presence of five sub-orbital periodicities. The longest period, P1 = 54.4 min, always observed, could be the beat period between the orbital period and the white dwarf (WD) spin period that we assume to be P2 = 33.4 min. The other suborbital periods could be orbital sidebands with respect to P2 and/or correspond to Keplerian resonance radii. We suggest that in its post-outburst state, characterized by higher mass transfer rate, RW UMi is an asynchronous intermediate polar with a truncated accretion disc. If the magnetic momentum of the WD is $μ_{34} \sim 0.8$, in its quiescent pre-outburst state, the nova would appear as a discless, synchronous intermediate polar.

astro-ph↗

arXiv1999

Parametric Resonance in the Drift Motion of an Ionic Bubble in near critical Ar Gas

The drift mobility of the negative oxygen ion in dense Argon gas near the liquid-vapor critical point has been measured as a function of the density. Near the critical temperature the zero-field density-normalized ion mobility shows a deep minimum at a density smaller than the critical one. This phenomenon was previously intepreted as the result of the formation of a correlated cluster of Argon atoms around the ion because of the strong electrostriction exerted by the ion on the highly polarizable and compressible gas. We now suggest that a possible alternative explanation is related to the onset of a parametric resonance of a bubble surrounding the ion. At resonance a large amount of energy is dissipated by sound waves in addition to viscous dissipation processes, resulting in the large mobility drop observed.

physics.plasm-ph↗