Parabolic deformable mirror testbed for the ExoSpec project

Abstract

ExoSpec Project is a NASA Headquarters directed work package that links four different tasks at Goddard space flight center to enable future missions to more efficiently characterize directly imaged exoplanets. One of the tasks is the development of parabolic deformable mirrors to improve on the current state-of-the-art wavefront sensing and control implementations that are baselined to have two high actuator count flat deformable mirrors (DMs). To effectively control both amplitude and phase aberrations, the flat DMs need to have a large separation distance. This large separation poses packaging challenges to missions designed to image rocky exoplanets at larger angular separations. To eliminate this large separation, the parabolic DM architecture makes the off-axis imaging elements in the optical train are controllable. Simulations also show performance enhancements with the architecture change; larger bandwidths have been shown to be controllable with the parabolic DMs and the number of required actuators can be reduced. With a 32x32 pupil flat DM and two 16x16 parabolic DMs, we could dig a 5-12 λ/D dark hole at 35% bandwidth. In addition to addressing the packaging challenge faced by future coronagraph missions, reducing the number of actuators reduces both cost and risk of having the entire coronagraph instrument’s performance depend on two high-actuator count DMs. To test these simulations, Goddard is building a testbed and has a vendor working on manufacturing the parabolic DM. Here we present these simulations, the current testbed performance, and the development plan to incorporate and test the parabolic DMs.