High fidelity modeling of Lyot low-order wavefront control for space-borne coronagraphy

Abstract

The last twenty years has seen a significant increase in the development of high-contrast imaging systems to enable the direct imaging of exoplanets around nearby stars. This remains a technically challenging feat due to a coronagraph’s sensitivity to both low and high spatial frequency aberrations, often requiring stability below 1 nm for contrasts on the order of 1E-8 to detect exoplanets in reflected light. Due to structural vibrations and deformations from environmental changes, these levels of stability cannot be achieved through observatory structural and opto-mechanical designs alone. Instead, low order wavefront control is needed to maintain pointing and a stable wavefront, thereby minimizing beamwalk and leakage around the coronagraph’s focal plane mask. Here, we demonstrate how the low order wavefront control is modeled for a vortex coronagraph with high fidelity in the time domain to ensure the coronagraph is capable of maintaining pointing stability and other low order Zernike aberrations. These modeling efforts include: an optical model of the vortex coronagraph with a deformable mirror, dynamic wavefront error injection, a detector model to generate noisy images, blurring from sub-frame dynamics, camera and controller latency, and transfer functions for the steering mirror(s). This modeling approach can also be generalized to other wavefront sensing architectures.