Broadband Vector Vortex Coronagraph Testing at NASA's High Contrast Imaging Testbed Facility

TL;DR

This paper reports laboratory testing of a vector vortex coronagraph achieving unprecedented contrast levels, advancing the technology toward direct imaging of Earth-like exoplanets with future space telescopes.

Contribution

It demonstrates significant improvements in contrast performance of liquid crystal vector vortex waveplates in laboratory conditions, approaching the levels needed for exoplanet imaging.

Findings

Achieved raw contrast of 1.6×10⁻⁹ in 10% bandwidth

Achieved raw contrast of 5.9×10⁻⁹ in 20% bandwidth

Demonstrated a tenfold improvement over previous results

Abstract

The unparalleled theoretical performance of an ideal vector vortex coronagraph makes it one of the most promising technologies for directly imaging exoplanets with a future, off-axis space telescope. However, the image contrast required for observing the light reflected from Earth-sized planets ($\sim10^{-10}$) has yet to be demonstrated in a laboratory setting. With recent advances in the manufacturing of liquid crystal vector vortex waveplates as well as system-level performance improvements on our testbeds, we have achieved raw contrast of 1.6$\times10^{-9}$ and 5.9$\times10^{-9}$ in 10% and 20% optical bandwidths, respectively, averaged over 3-10$\lambda/D$ separations on one side of the pseudo-star. The former represents a factor of 10 improvement over the previously reported performance. We show experimental comparisons of the contrast achieved as a function of spectral bandwidth. We provide estimates of the limiting error terms and discuss the improvements needed to close the gap in contrast performance required for future exoplanet imaging space telescopes.