Welcome to the SCExAO project webpage!
Image of various components in SCExAO: (Left) 2000 actuator deformable mirror (middle) IR/visible dichroic splitter, fixed pupil
mask and delivery fiber for internal calibration source (foreground) (Right) Starbowl wheel.
Applying to use SCExAO? See science ready capabilities
under the "current capabilities" link for details
The SCExAO acronym stands for Subaru Telescope Extreme Adaptive Optics project. It is an active, ongoing effort to equip the Subaru Telescope with a high performance coronagraph and a series of wavefront control solutions that make an optimal use of the angular resolution that an 8-meter telescope has to offer. The ultimate science goal of SCExAO is the direct imaging of extrasolar planets around stars at a separation corresponding to the diffraction limit of the telescope in the near infrared, more specifically in the y-K-bands, at 0.95-2.4 μm. Two other large scale projects with comparable science goals are currently being assembled: The Gemini Planet Imager (GPI) that is currently being commissioned at the Gemini South Telescope and the SPHERE for the VLT. Instead of competing with these two heavyweight projects, SCExAO is trying to offer complementary capabilities, by focusing on very small angular separation: 40 - 500 milli-arcseconds.
SCExAO can do this because it implements several a high efficiency, low inner working angle coronagraphs. The workhorse of these units is the PIAA (Phase Induced Amplitude Apodization), invented by Olivier Guyon (SCExAO project PI), that exhibits an inner working angle that is as close to the diffraction limit as you can get (1 λ/D). The PIAA used in SCExAO was designed to provide a raw-contrast of 106 at 1.5 λ/D. In addition SCExAO offers other low inner working angle coronagraphs such as the Vortex, Four-Quadrant Phase Mask and 8-Octant Phase Mask versions. In addition it also offers a shaped pupil coronagraph for high contrast work where the inner working angle can be relaxed.
While reaching such a high level of contrast has already been demonstrated in the well controlled environment of the laboratory, it is unlikely to be achieved at the telescope, as wavefront aberrations induced by the atmosphere and the optics of the telescope quickly degrade image quality. To remedy this, SCExAO is/has developed a series of appropriate measures, for wavefront sensing and control. SCExAO uses:
- The Subaru Telescope facility AO system called AO188, operating at visible wavelengths, to provide the initial wavefront correction, which considerably reduces the strain on the SCExAO components.
- A Coronagraphic Low-Order Wavefront Sensor (CLOWFS) for ultra-fine pointing control, operating in the IR and using the light rejected by the focal plane mask of the coronagraph to fine tune the tip/tilt.
- A visible pyramid-based High Order Wavefront sensor (only available in the second phase of the project) to cancel out the dynamic atmospherically induced aberrations responsible for the presence of fast speckles.
- Speckle probing techniques, that use commands sent to a deformable mirror to "probe" the speckles the coherence of the speckles in the field, and eventually erase them. This also offers the ability for precise astrometry.
SCExAO has been undergoing commissioning of various modules since 2011. Most runs have been hampered by weather but the few that haven't, have been very successful. The modules/features that have been commissioned and can now be offered for open use are listed in the following section. Beneath this is a list of the modules we are currently engineering and hope to offer in the not to distant future.
Image of SCExAO mounted at the Nasmyth IR platform. AO188 can be seen to the left (large black box), SCExAO is the
dual level instrument in the middle (black and white panels) and HiCIAO is to the right of the image (Blue instrument).
The new pyramid wavefront sensor underwent significant testing during the November engineering/science run. Significant progress was made throughout the run and in the end the loop was closed on up to 1030 modes (combination of Zernike and Fourier modes) on the internal source with strong turbulence! The internal source was used only because the weather closed in when we got the loop working but nonetheless we demonstrated that starting from an average Strehl of 23% (300 nm RMS wavefront error on turbulence simulator) we could drive the AO corrected Strehl to 95% on average! The figure below shows the Strehl for data cubes before and after the loop was closed on the internal source with turbulence. This is a great milestone and with further upgrades to the software we are confident and on-sky demonstration is not far off. Read more here.
Strehl ratio from internal science camera images while the PyWFS loop was open and closed. The Open loop and Closed loop regime are clearly highlighted.
For comparison the typical Strehl ratio achieved by AO188 is also displayed. Data taken in internal source with turbulence.
Pyramid wavefront sensor rebuilt. This includes the addition of a proper pyramid optic leant to us by Jared Males and Laird Close from MagAO (massive mahalo), the brand new OCAM2K and new control electronics for synchronizing the tip/tilt mirror with the frame acquisition. The first pupil image taken with the new pyramid optic and camera is shown below. The image is very clean and clearly there is little diffraction between the pupils which indicates a high quality pyramid shaped optic. Read more here.
First image of the pupil with the new Pyramid wavefront sensor system.
OCAM2K has been delivered ahead of time by FIRSTLight Imaging! A massive mahalo to the team for their hardwork.
(Left) OCAM 2k delivered to Subaru Telescope.(Right) OCAM 2k and accessories.
The SCExAO team and collaborators were awarded ~$US1.1M to build an MKIDS detector by the JSPS! This coupled with the $250k awarded by the NAOJ is enough to fund the development of a dedicated 20 pix MKID detector for exoplanet science.
The April observing run was a great success. We revalidated speckle nulling and the LOWFS on-sky with convincing results and VAMPIRES collected a ton of data following its upgrades as well. The icing on the cake was the demonstration of closed loop operation of the high order wavefront sensor (non-modulated pyramid wavefront sensor). With the implementation of 5 GPU's since the December run, we managed to drive the PyWFS at 800 Hz on 200 modes on-sky. We tested the loops performance to cancel aberrations by adding varying static wavefront errors via our deformable mirror on top of the pre-existing aberrations and then watched the restoration of the PSF and the applied volt map post correction. Next steps include adding regularization to prevent actuators in and around the pupil edges from saturating, eliminating existing delays in the loop and applying off-sky response matrices to attempt to get extreme AO correction on the coming June run. Stay tuned! In addition we observed significant improvements in PSF stability as a result of the HiCIAO vibration isolation upgrades. Great success!
The HiCIAO camera was overhauled to include a dual bellows vibration isolation unit. More information can be found on the vibrations page.
(Left) The new dual bellows vibration isolation system installed on HiCIAO.
We received funding to purchase two state-of-the-art cameras, namely OCAM 2K and MKIDS. OCAM 2K (FirstLight) is one of the most advanced visible cameras (frame rate of 3.7 kHz with binning, 0.3e- read noise, <0.01e- dark current and very high quantum efficiency between 500 and 900 nm). This camera will be used to replace the Andor Zyla currently used for the non-modulated pyramid wavefront sensor and boost performance significantly. This camera is expected to be delivered in late May 2014 and installed and running a few months after this date. MKIDS stands for Microwave Kinetic Inductance Detector and is a photon counting, energy discriminating superconducting based technology. It is being developed by Prof. Ben Mazin's group at UC Santa Barabara and we are fortunate enough to work with them developing a specific unit for SCExAO. This camera will replace the current high frame rate/speckle nulling camera. With the boost in sensitivity and speed, we will be able to do fast wavefront control and calibration and push speckle nulling and even focal plane wavefront sensing to the limit. MKIDS will take several years to build and test.
(Left) OCAM 2k (Image taken by FirstLight Advanced Imaging). (Middle) MKIDS detector.
(Right) Prof. Ben Mazin with the entire MKIDS camera assembly (Images taken by Mazin's group at UCSB).