Demonstration of broadband contrast at 1.2 $\lambda$/D and greater for the EXCEDE Starlight Suppression System

TL;DR

This paper demonstrates broadband high-contrast imaging capabilities of the EXCEDE starlight suppression system at 1.2 $ ext{to}$ 2 $ imes$ the diffraction limit, achieving stable contrast levels suitable for exoplanet observation.

Contribution

It reports the first experimental broadband contrast results for the EXCEDE system in a vacuum environment, validating simulation models and demonstrating stable, repeatable performance.

Findings

Achieved median contrast of 1e-5 between 1.2 and 2.0 λ/D

Achieved contrast of 3e-7 between 2 and 11 λ/D

Results are stable and consistent with simulation predictions.

Abstract

The EXoplanetary Circumstellar Environments and Disk Explorer (EXCEDE) science mission concept uses a visible-wavelength Phase-Induced Amplitude Apodization (PIAA) coronagraph to enable high-contrast imaging of circumstellar debris systems and some giant planets at angular separations reaching into the habitable zones of some of the nearest stars. We report on the experimental results obtained in the vacuum chamber at the Lockheed Martin Advanced Technology Center in 10% broadband light centered about 650 nm, with a median contrast of $1 \times 10^{-5}$ between 1.2 and 2.0 $\lambda$/D simultaneously with $3 \times 10^{-7}$ contrast between 2 and 11 $\lambda/D$ for a single-sided dark hole using a deformable mirror (DM) upstream of the PIAA coronagraph. These results are stable and repeatable as demonstrated by three measurements runs with DM settings set from scratch and maintained on the best 90% out of the 1000 collected frames. We compare the reduced experimental data with simulation results from modeling observed experimental limits; observed performance is consistent with uncorrected low-order modes not estimated by the Low Order Wavefront Sensor (LOWFS). Modeled sensitivity to bandwidth and residual tip/tilt modes is well-matched to the experiment.