White-light demonstration of one hundred parts per billion irradiance suppression in air by new starshade occulters

Abstract

A new mission concept for direct imaging of exo-solar planets called New Worlds Observer (NWO) has been proposed. It involves flying a meter-class space telescope in formation with a newly-conceived, specially-shaped, deployable star-occulting shade several meters across at a separation of some tens of thousands of kilometers. The telescope would make its observations from behind the starshade in a volume of high suppression of incident irradiance from the star around which planets orbit. For an efficacious mission, the required level of irradiance suppression by the starshade is of order 0.1 to 10 parts per billion in broadband light. We discuss an experiment to accurately measure the irradiance suppression ratio at the null position behind candidate starshade forms to these levels. We also present results of broadband measurements which demonstrated suppression levels of less than 100 parts per billion in air using the Sun as a light source. A simulated spatial irradiance distribution surrounding the null from an analytical model developed for starshades is compared with a photograph of actual irradiance captured in situ behind a candidate starshade.