Occulter-Based High-Contrast Exoplanet Imaging: Design, Scaling, and Performance Verification

Abstract

Over the last two decades, a large number of exoplanets have been confirmed with the rate of discovery increasing in recent years primarily as new instruments with improved sensitivities have become available. Direct imaging of an Earth-like planet is now an important goal of the science community. This is a challenging problem for two primary reasons. First, the intensity ratio between the bright star and its dim Earth-like companion is expected to be approximately ten orders of magnitude and, second, the angular separation to the star is very small.

An external occulter is a specially-shaped spacecraft that is flown in formation with a telescope in order to block most of the starlight before it reaches the entrance pupil thereby allowing planetary light outside of the occulter's inner working angle to become visible. Designing a shape for the occulter spacecraft to enable suppression over a wavelength band of interest requires modeling through scalar diffraction theory. Typical designs feature occulters that are tens of meters across at a separation of tens of thousands of kilometers from the space telescope.

In this dissertation, we focus on occulter design and scaling to enable experimental optical verification of occulters in the laboratory. We provide experimental results that establish a $10^{-5}$ suppression level in the pupil and $10^{-10}$ contrast in the focal plane, which are both approximately two orders of magnitude below the ideal performance of the testbed. We use numerical simulation to study the sensitivity of the occulter design in the laboratory and determine that performance is feature-size limited. We provide the design of a longer and flight-like occulter experiment, and study its sensitivity to determine the expected performance.