Abstract
In this paper, after briefly reviewing the theory of vectorial vortices, we describe our technological approach to generating the necessary phase helix, and report results obtained with the first optical vectorial vortex coronagraph (OVVC) in the laboratory. To implement the geometrical phase ramp, we make use of Liquid Crystal Polymers (LCP), which we believe to be the most efficient technological path to quickly synthesize optical vectorial vortices of virtually any topological charge. With the first prototype device of topological charge 2, a maximum peak-to-peak attenuation of 1.4x10(-2) and a residual light level of 3x10(-5) at an angular separation of 3.5 lambda/d (at which point our current noise floor is reached) have been obtained at a wavelength of 1.55 microm. These results demonstrate the validity of using space-variant birefringence distributions to generate a new family of coronagraphs usable in natural unpolarized light, opening a path to high performance coronagraphs that are achromatic and have low-sensitivity to low-order wavefront aberrations.
Highlights
Coronagraphy, a means of suppressing bright starlight so as to search for faint companions or circumstellar material, has garnered much interest in the past decade
In the pupil plane coronagraph family, there are: (a) amplitude apodization, and the phase induced amplitude apodization (PIAA) approach, in which the mirrors are warped to reshape the distribution of light in the pupil to yield an apodized shape, (b) pupil plane phase apodization, and in the focal plane coronagraph family, there are (c) amplitude masks, and (d) phase mask coronagraphs of various types
In [4], we demonstrated that the creation of a vortex of any even topological charge l at the focal plane can lead to a perfect coronagraph in the ideal case
Summary
Coronagraphy, a means of suppressing bright starlight so as to search for faint companions or circumstellar material, has garnered much interest in the past decade. An optical vortex is a phase singularity in an optical field, a point of zero intensity, resulting from a phase screw dislocation of the form eilθ , with l being the so-called topological charge, and θ the azimuthal coordinate This anomaly forces the intensity to vanish by a total destructive interference, creating a dark core. In [4], we demonstrated that the creation of a vortex of any even topological charge l at the focal plane can lead to a perfect coronagraph in the ideal case (no further phase aberrations in the system). This result has been confirmed later on by [5, 6]. There are two kinds of optical vortices (and of elements that induce them):
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