A Broadband Scalar Vortex Coronagraph

TL;DR

This paper introduces a new broadband scalar vortex coronagraph that achieves deep nulling and small inner working angle, enabling improved imaging of faint objects like exoplanets over a broad wavelength range.

Contribution

It proposes and experimentally demonstrates a novel broadband optical scalar vortex coronagraph using phase gratings to control chromatic dispersion, achieving high contrast over 120 nm bandwidth.

Findings

Peak-to-peak attenuation below 10^-3 over 120 nm bandwidth

Inner working angle of approximately λ/D

Raw contrast of 11.5 magnitudes at 2λ/D

Abstract

Broadband coronagraphy with deep nulling and small inner working angle has the potential of delivering images and spectra of exoplanets and other faint objects. In recent years, many coronagraphic schemes have been proposed, the most promising being the optical vortex phase mask coronagraphs. In this paper, a new scheme of broadband optical scalar vortex coronagraph is proposed and characterized experimentally in the laboratory. Our setup employs a pair of computer generated phase gratings (one of them containing a singularity) to control the chromatic dispersion of phase plates and achieves a constant peak-to-peak attenuation below $1\cdot 10^{-3}$ over a bandwidth of 120 nm centered at 700 nm. An inner working angle of ~\lambda/D is demonstrated along with a raw contrast of 11.5 magnitudes at 2\lambda/D.