Design and laboratory demonstration of an achromatic vector vortex coronagraph

Abstract

Abstract:A vector vortex coronagraph (VVC) is one of promising means for imaging extremely faint objects around bright stars such as exoplanets. We present a design of an achromatic VVC, in which an axially-symmetric half-wave plate (AHP) is placed between crossed polarization filters (circular polarizer and analyzer). The circular polarizer and the analyzer are both composed of a polarizer and a quarter-wave plate (QWP). We demonstrate, via Jones calculus and Fourier analysis, that the achromatic stellar elimination can theoretically be realized by optimal polarization filters, even when chromatic AHP and QWPs are used. We carried out laboratory demonstrations of the designed VVC using a photonic-crystal AHP. As a result, we observed achromatic coronagraphic performance, a light suppression level of 7 × 10 −5 , over a wavelength from 543 nm to 633 nm.

Vortex coronagraphy from self-engineered liquid crystal spin-orbit masks

“…The former case refers to the helical shaping of the wavefront from a refractive phase mask, whereas the latter one exploits the polarization properties of space-variant birefringent optical elements. Indeed, inhomogeneous anisotropic phase masks endowed with azimuthal optical axis orientation of the form ψ(φ) = mφ with m half-integer and associated with half-wave birefringent phase retardation lead to a vortex mask of charge = 2σm for incident on-axis circularly polarized light beam with helicity σ = ±1, as originally shown in [8] using form birefringence (subwavelength grating of dielectric materials) and, in [9], using true birefringence.The achromatic features of the vectorial option versus its scalar counterpart [10,11] have eventually led to equip state-of-the-art large instruments such as Keck, Subaru, Hale, Large Binocular Telescope, and Very Large Telescope with vectorial vortex coronagraphs. In practice, all these installations exploit vortex masks obtained either from brute force nanofabrication, where form birefringence arises from subwavelength material structuring [8], or liquid crystal polymers technology, where true birefringence is patterned on demand [12].…”

“…The achromatic features of the vectorial option versus its scalar counterpart [10,11] have eventually led to equip state-of-the-art large instruments such as Keck, Subaru, Hale, Large Binocular Telescope, and Very Large Telescope with vectorial vortex coronagraphs. In practice, all these installations exploit vortex masks obtained either from brute force nanofabrication, where form birefringence arises from subwavelength material structuring [8], or liquid crystal polymers technology, where true birefringence is patterned on demand [12].…”

A coronagraph system with unbalanced nulling interferometer: progress of optics and control method

“…A Shack-Hartman pupil-plane wavefront sensor (WFS) using a cooled CCD camera (Bitran BU-40L-14) with a micro lens array (Thorlabs MLA150-5C) is placed after the DMs by picking up a part of the light by a beam splitter to monitor the wavefront into the coronagraph. An achromatic coronagraph with vortex phase mask (VPM) 12 or an eight-octant phase mask (8OPM) 13 is used at the last stage. These masks are half-wave plates manufactured by photonic crystal technique (Photonic Lattice Inc.) and work as achromatic phase masks when used with a polarizer and an analyzer.…”

The multistage and ring-apodized vortex coronagraph: two simple, small-angle coronagraphic solutions for heavily obscured apertures

“…Three technological approaches are currently used to manufacture the VVC: 3 liquid crystal polymers, 26 subwavelength gratings, 1, 28 and photonic crystals. 29,30 Each one of these technological choices has advantages and drawbacks, enumerated in Ref. 3, and practical vortex devices that have already provided very high contrast with unobscured apertures are already available.…”