WFIRST low order wavefront sensing and control dynamic testbed performance under the flight like photon flux

Abstract

To maintain the required performance for the WFIRST Coronagraph Instrument (CGI) in a realistic space environment, a Low Order Wavefront Sensing and Control (LOWFS/C) subsystem is necessary. The WFIRST CGI LOWFS/C subsystem will use the Zernike wavefront sensor, which has a phase-shifting disk combined with the coronagraph’s focal plane mask, to sense the low-order wavefront drift and line-of-sight (LoS) error using the rejected starlight. The dynamic tests on JPL’s Occulting Mask Coronagraph (OMC) Testbed have demonstrated that LOWFS/C can maintain coronagraph contrast to better than 10-8 in presence of WFIRST-like line of sight and low order wavefront disturbances in both Shaped Pupil Coronagraph (SPC) and Hybrid Lyot Coronagraph (HLC) modes. However, the previous dynamic tests have been done using a bright source with photon flux equivalent to stellar magnitude of MV = -3.5. The LOWFS/C technology development on the OMC testbed has since then concentrated in evaluating and improving the LOWFS/C performance under the realistic photon flux that is equivalent to WFIRST Coronagraph target stars. Our recent testbed tests have demonstrated that the LOWFS/C can work cohesively with the stellar light suppression wavefront control, which brings broad band coronagraph contrast from ~1x10-6 to 6x10-9, while LOWF/C is simultaneously suppressing the WFIRST like LoS and low order wavefront drift disturbances on a source that photon flux is equivalent to a MV = 2 star. This lab demonstration mimics the CGI initial dark hole establish process on a bright reference star. We have also demonstrated on the testbed that LOWFS/C can maintain the coronagraph contrast by suppressing the WFIRST like line-of-sight disturbances on a fainter MV = 5 star. This mimics scenario of CGI science target observations. In this paper we will present the recent dynamic testbed performance results of LOWFS/C LoS loops and low order wavefront error correction loop on the flight like photon flux.