Dark Hole Algorithms Working Group for Coronagraph Instrument

Purpose

Wavefront sensing and control algorithms are an essential component of the Roman Coronagraph Technology Demonstration, as the mission presents our first opportunity to test the performance limits of active starlight suppression with a space observatory. Future exoplanet imaging missions will benefit from assessments of the practical trade-offs of different techniques for sensing and compensating wavefront disturbances in the coronagraph dark hole. Further insights may be gained by investigating how these algorithms interact with the actual telescope and instrument hardware in the presence of unmodeled disturbances and error sources.

In 2020 the design of both the Roman Coronagraph Instrument and its associated ground systems reached a sufficient level of maturity to define clear constraints on the baseline control strategy, along with potential paths to contribute algorithm modifications in collaboration with the Coronagraph project team. The Dark Hole Algorithms Working Group was formed to help focus the coronagraph research community's attention on the opportunity to enhance the technology demonstration through alternative wavefront sensing and control algorithms, while keeping in view the Roman-specific "ground-in-the-loop" operation and instrument characteristics. As a caveat, we note that NASA has not yet guaranteed support for demonstrating non-baseline wavefront sensing and control algorithms.

The working group has met four times via video conference during 2020-2021 for contributed presentations, with time reserved for questions and discussion. There were typically about 25 attendees drawn from project staff and researchers from NASA centers and universities. The meetings will resume in the middle of 2022; contact Neil Zimmerman (neil.t.zimmerman@nasa.gov) if you are interested in joining the announcement list. In the meantime, we summarize here the topics and discussions of past meetings, with links to presentation materials.

A raw high contrast image derived in testbed measurements (left) and a plot (right) of the total contrast demonstrating that the unmodulated light (red) dominates the modulated light (blue). Testbed experiments are described in Byoung-Joon Seo, Eric Cady, Brian Gordon, et al., “Hybrid Lyot coronagraph for WFIRST: high-contrast broadband testbed demonstration”. Proceedings Volume 10400, Techniques and Instrumentation for Detection of Exoplanets VIII; 104000F (2017) https://doi.org/10.1117/12.2274687