Laboratory demonstration of the triple-grating vector vortex coronagraph

TL;DR

This paper demonstrates a novel triple-grating vector vortex coronagraph in laboratory settings, showing promising contrast performance over a broad spectral bandwidth for potential exoplanet imaging.

Contribution

The study introduces and tests a triple-grating vector vortex coronagraph prototype that reduces polarization leakage across large spectral bandwidths, advancing coronagraph technology for exoplanet observation.

Findings

Achieved contrast of 2×10⁻⁸ at IACT

Achieved contrast of 6×10⁻⁸ at SCoOB

Identified manufacturing errors and mitigation strategies

Abstract

The future Habitable Worlds Observatory aims to characterize the atmospheres of rocky exoplanets around solar-type stars. The vector vortex coronagraph (VVC) is a main candidate to reach the required contrast of $10^{-10}$. However, the VVC requires polarization filtering and every observing band requires a different VVC. The triple-grating vector vortex coronagraph (tgVVC) aims to mitigate these limitations by combining multiple gratings that minimize the polarization leakage over a large spectral bandwidth. In this paper, we present laboratory results of a tgVVC prototype using the In-Air Coronagraphic Testbed (IACT) facility at NASA's Jet Propulsion Laboratory and the Space Coronagraph Optical Bench (SCoOB) at the University of Arizona Space Astrophysics Lab (UASAL). We study the coronagraphic performance with polarization filtering at 633 nm and reach a similar average contrast of $2 \times 10^{-8}$ between 3-18 $\lambda/D$ at the IACT, and $6 \times 10^{-8}$ between 3-14 $\lambda/D$ at SCoOB. We explore the limitations of the tgVVC by comparing the testbed results. We report on other manufacturing errors and ways to mitigate their impact.