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To directly image and characterize exoplanets, many developments of high-contrast imaging (HCI) systems are ongoing for current ground-based telescopes as well as future extremely large telescopes and space-based telescopes. Despite recent developments in HCI, the contrast of the HCI systems is limited by non-common path aberrations (NCPAs) and residual errors of the adaptive optics (AO) system. In order to overcome these limitations, HCI systems need focal plane wavefront sensing and control (FPWFS&C) techniques.
We present the implementation of two FPWFS&C techniques, electric field conjugation (EFC) and spatial linear dark field control (LDFC), on the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument. First, we generate a half-dark hole in the focal plane image using EFC. Once the bright field and dark field (dark hole) have been established by EFC, as a second step, we deploy spatial LDFC to maintain the contrast of the half-dark hole generated by EFC. We could also use EFC to preserve the contrast of the dark hole, but it requires field modulation, which interferes with the science image acquisition. Because of this reason, we use spatial LDFC as an alternative way to maintain the contrast without modulation.
In actual demonstrations, we obtained a dark hole contrast of ∼2×10−7 with a classical Lyot coronagraph of 114 mas diameter, at a 1550 nm wavelength using EFC. This result is the first EFC implementation and the deepest contrast obtained on the SCExAO testbed. Using spatial LDFC, we also ideally removed focal plane speckles generated by static phase error and restored the initial contrast. Our results provide a promising path forward to generating the high-contrast dark hole using EFC and stabilizing the contrast of the dark hole without interrupting the science acquisition using spatial LDFC.
Linearized Analytical Phase Diversity : towards lab and on-sky demonstration on the Subaru Telescope
SCExAO, an instrument with a dual purpose: perform cutting-edge science and develop new technologies
Since 2006, PERSEE (PEGASE Experiment for Research and Stabilization of Extreme Extinction) laboratory test bench is under development by a consortium composed of Centre National d’Etudes Spatiales (CNES), Institut d’Astrophysique Spatiale (IAS), Observatoire de Paris-Meudon (LESIA), Observatoire de la Côte d’Azur (OCA), Office National d’Etudes et de Recherches Aérospatiales (ONERA), and Thalès Alénia Space (TAS) [8]. It is mainly funded by CNES R&D. PERSEE couples an infrared wide band nulling interferometer with local OPD and tip/tilt control loops and a free flying Guidance Navigation and Control (GNC) simulator able to introduce realistic disturbances. Although it was designed in the framework of the PEGASE free flying space mission, PERSEE can adapt very easily to other contexts like FKSI (in space, with a 10 m long beam structure) or ALADDIN [9] (on ground, in Antarctica) because the optical designs of all those missions are very similar. After a short description of the experimental setup, we will present first the results obtained in an intermediate configuration with monochromatic light. Then we will present some preliminary results with polychromatic light. Last, we discuss some very first more general lessons we can already learn from this experiment.
Different approaches are being implemented to take care of these issues. The PID control of the image rotator has been tuned to reduce their high-frequency contribution. We are working with the telescope team to tune the motor drives and reduce the impact of the elevation encoder. A Linear Quadratic Gaussian controller (LQG, or Kalman filter) is also being implemented inside SCExAO to control these vibrations. These solutions will not only improve significantly SCExAOs performance, but will also help all the other instruments on the Subaru Telescope, especially the ones behind AO188. Ultimately, this study will also help the development of the TMT, as these two telescopes share very similar drives.
Previously, we have reported experimental results on the first milestone, the demonstration of EXCEDE contrast in monochromatic light in air and more recently in vacuum. In this paper, we report on the procedure and the experimental results obtained for our second milestone demonstration of the EXCEDE starlight suppression system carried in a vacuum chamber at the Lockheed Martin Advanced Technology Center. This includes high contrast performance demonstrations at 1.2 λD, which includes a lab demonstration of 1x10-5 median contrast between 1.2 and 2.0 λD simultaneously with 3x10-7 median contrast between 2 and 11 λD in 10% bandwidth polychromatic light centered at 650 nm for a single-sided dark zone. The results are stable and repeatable as demonstrated by three measurement runs with DM settings set from scratch and maintained on the best 90% out of the 1000 collected frames per run. We compare reduced experimental data with simulation results from modeling experimental limits.
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