Optical vortices with starlight

Abstract

Aims. In this paper we present our first observations at the Asiago 122 cm telescope of = 1 optical vortices generated with starlight beams. Methods. We used a fork-hologram blazed at the first diffraction order as a phase modifying device. The multiple system Rasalgethi (α Herculis) in white light and the single star Arcturus (α Bootis) through a 300 Å bandpass were observed using a fast CCD camera. In the first case we could adopt the Lucky Imaging approach to partially correct for seeing effects. Results. For both stars, the optical vortices could be clearly detected above the smearing caused by the mediocre seeing conditions. The profiles of the optical vortices produced by the beams of the two main components of the α Her system are consistent with numerically simulated on-axis and off-axis optical vortices. The optical vortices produced by α Boo can also be reproduced by numerical simulations. Our experiments confirm that the ratio between the intensity peaks of an optical vortex can be extremely sensitive to off-axis displacements of the beam. Conclusions. Our results give insights for future astronomical applications of optical vortices both for space telescopes and groundbased telescopes with good seeing conditions and adaptive optics devices. The properties of optical vortices can be used to perform high precision astrometry and tip/tilt correction of the isoplanatic field. We are now designing a = 2 optical vortex coronagraph around a continuous spiral phase plate. We also point out that optical vortices could find extremely interesting applications also in the infrared and radio wavelengths.

Measuring the orbital angular momentum of partially coherent optical vortices through singularities in their cross-spectral density functions

“…More recently, OAM has seen increasing applications in free-space information transfer and communications [7,8]. On the other hand, the interest for OAM of light in astronomy and astrophysics has grown [9,10]. Optical vortices generated from starlight beams have been observed at the Asiago 122 cm telescope [9], and the properties of optical vortices have found interesting applications in astronomical coronography [10].…”

“…On the other hand, the interest for OAM of light in astronomy and astrophysics has grown [9,10]. Optical vortices generated from starlight beams have been observed at the Asiago 122 cm telescope [9], and the properties of optical vortices have found interesting applications in astronomical coronography [10]. The measurement of the azimuthal index m associated with a given vortex field is crucial for all these fields and may yield interesting new studies in astrophysics [11].…”

Optical vortex generation by volume holographic elements with embedded phase singularity: Effects of misalignments

“…Beams with the OVs reveal many useful properties which make them promising for a lot of practical applications: capturing and manipulation of microparticles [3][4][5], measurement of small displacements and exact localization of optical inhomogeneities [6][7][8][9], as well as improving resolution of spatially overlapping optical signals [10][11][12][13] and encoding or processing information [14][15][16]. This entails a necessity for regular and reliable means of their generation.…”

“…Besides, the properties of the OV-beams obtained under conditions of HE misalignment can be profitably exploited. For the OV-beams generated with thin HEs, this has been demonstrated for metrological and astronomical applications [9][10][11][12][13], as well as for discriminating different OV-beams in systems of information transfer and processing [14][15][16][38][39][40][41]. All of these points make it highly relevant to study in detail the role and significance of the diffracted-beam distortions appearing due to nonideal arrangement of the incident beam and the HE the with EPS.…”

Characterizing topological charge of optical vortex using non-uniformly distributed multi-pinhole plate

“…These pinholes drag and intermix their surrounding space and time. In the diffraction-limited regime [25] , our method would be an efficient way for the detection and measurement of the twisted light by using a few telescopes; thus, allowing a direct observational demonstration of the existence of rotating black holes.…”