PSI Technology Development at Keck II
Predictive Wavefront Control: Modern AO systems typically suffer from millisecond time lags between measuring and correcting for atmospheric turbulence; predictive wavefront control compensates for these time lags using previous wavefront measurements. Predictive control is currently being developed as part of the pyramid wavefront sensor real time control system at Keck II, with an on-sky contrast improvement of 2-3X demonstrated in van Kooten et al. 2021. Predictive control based on the Empirical Orthogonal Functions (Guyon & Males 2017) and the linear minimum mean square error (van Kooten et al. 2019) are under development at Keck. This work is funded by the Heising-Simons Foundation and the National Science Foundation.
Speckle Nulling: Uncorrected optical aberrations appearing as bright speckles in the coronagraphic focal plane are a major source of systematic error in high contrast imaging systems. Such speckles commonly arise from imperfections in optics downstream of the wavefront sensor, and can only be measured with focal plane wavefront sensing (FPWFS). Bottom et al. 2016 demonstrated FPWFS by perturbing the DM to create interferometric patterns in the focal plane. Recently, Bos et al. 2021 measured wavefront errors in the focal plane via the Fast and the Furious algorithm (Keller et al. 2021, Korkiakoski et al. 2014). This work is funded by the National Science Foundation, the Heising-Simons Foundation, and the European Research Council.
Primary Mirror Segment Phasing: Keck is the only segmented-mirror telescope with high contrast imaging capabilities. As such, it is a crucial testbed for characterizing and mitigating the impacts of segment phasing errors on the contrast. Ragland et al. 2018 combined non-coronagraphic AO science images with detailed AO modeling to reconstruct periodic residual segment piston errors. Recently, a Zernike wavefront sensor was installed inside KPIC. A Caltech, JPL, and UCSC team is currently working to reconstruct segment piston and tip/tilt errors using the Zernike sensor. This work is funded by the Heising-Simons Foundation and the National Science Foundation.