SCExAO: Subaru Coronagraphic Extreme Adaptive Optics
The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) is a high-contrast imaging system for directly detecting exoplanets that are close to their host star. It is one of the instruments of the Subaru Telescope on Mauna Kea on Hawaii.
SCExAO relies on an 18-millimeter deformable mirror with 2000 actuators. Wave front disturbances that are caused by atmospheric movement in the telescope’s field of view are detected by a four sided prism, formed like a pyramid, and corrected by moving the mirror actuators 2000 to 3000 times per second.
At LEOPARD we are working on focal-plane wavefront sensing techniques that measures wave front disturbances caused by the optics in the instrument itself. These instrumental aberrations evolve over timescales of minutes to hours due to temperature and humidity changes in the instrument and are not measured by the pyramid wavefront sensor mentioned above. With these techniques we use the images of the star on the camera to measure these aberrations. They can be corrected by control of the actuators on the deformable mirror. It can improve the contrast during measurement with a factor of two to three.
SCExAO also makes use of a Vector Apodizing Phase Plate developed at LEOPARD. This liquid crystal optical element makes coronagraphy possible in combination with the adaptive optics system.
We hope that by developing and testing groundbreaking technology in SCExAO, we can find and characterize Earth-like exoplanets with the Extremely Large Telescope in the 2030s.
The image of a star ‘before’ and ‘after’ the use of the adaptive optics of SCExAO. Credit: SCExAO
People working with SCExAO:
Steven Bos
David Doelman
Frans Snik
External links: