Frédéric submitted:
The Subaru Coronagraphic Extreme Adaptive Optic (SCExAO) system : implementation and performances of the Coronographic Low Order Wave-Front Sensor
In order to achieve high-contrast imaging at small working angles using the HICiAO camera on the Subaru telescope, a Phase Induced Amplitude Apodization (PIAA) Coronograph system is currently being assembled. The Subaru Coronographic Extreme Adaptative Optic (SCExAO) system, scheduled to be installed on the telescope early spring 2010, is located between the Subaru Adaptive Optic system (AO-188) and the recently commissioned HICiAO camera. It is designed to achieve a 1e-6 contrast at separations less than 0.5". This high contrast coronographic imaging requires an accurate control of low order wave-front aberrations, such as tip-tilt and focus errors. Simulations and laboratory prototyping have shown that a Coronographic Low Order Wave-Front Sensor (CLOWFS), which uses a single defocused image of a reflective focal plane ring, can measure tip-tilt to an accuracy of 1e-3 lambda/D. We report the implementation and performances of the CLOWFS on the SCExAO system. Using both the CLOWFS camera as well as the science camera in the system, we quantify the accuracy of this system and its ability to successfully remove tip-tilt errors from the science image. We show that CLOWFS measurements can be used in post-processing to accurately remove coronographic leaks due to residual tip-tilt errors. We finally deduce the maximum contrast to be reached using the SCExAO system alongside the HICiAO camera and the AO-188 on the Subaru telescope.
Kaito submitted:
An 8 Octant Phase Mask coronagraph for the Subaru Coronagraphic Extreme AO (SCExAO) system: system design and expected performance
The 8 Octant Phase Mask (EOPM) coronagraph is among the highest performance coronagraph concepts, and combines high throughput, small inner working angle, and large discovery space. However, its application to ground based telescope such as Subaru Telescope is challenging due to pupil geometry (thick spider vanes and large central obstruction) and residual tip-tilt errors. We show that the Subaru Coronographic Extreme Adaptative Optic (SCExAO) system, scheduled to be installed on the telescope early spring 2010, includes key technologies which can solve these problems. SCExAO uses a spider removal plate (SRP) which translates four parts of the pupil with tilted plane parallel plates. The pupil central obstruction can be removed by a pupil remapping system similar to the PIAA optics already in the SCExAO system, which could be redesigned with no amplitude apodization. The 8OPM is inserted in the focal plane to divide a stellar image into eight-octant regions, and introduces a pi-phase difference between adjacent octants. This causes a self-destructive interference inside the pupil area on a following reimaged pupil plane. By using a reflective mask instead of a conventional opaque Lyot stop, the stellar light diffracted outside the pupil can be used for a Coronographic Low Order Wave-Front Sensor (CLOWFS) to accurately measure and correct tip-tilt errors. A modified inverse-PIAA system, located after the reimaged pupil plane, is used to remove off-axis aberrations and deliver a wide field of view.
We show that this 8OPM coronagraph architecture enables high contrast imaging at small working angle on the Subaru telescope. Our approach could be generalized to other phase mask type coronagraphs and other ground based telescopes.
We show that this 8OPM coronagraph architecture enables high contrast imaging at small working angle on the Subaru telescope. Our approach could be generalized to other phase mask type coronagraphs and other ground based telescopes.
The Subaru Coronagraphic Extreme AO (SCExAO) system: Visible Imaging Mode
The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system is an instrument designed to be inserted between the Subaru AO188 system and the infrared HiCIAO camera in order to greatly improve the contrast in the very close (less than 0.5") neighbourhood of stars.
Next to the infrared coronagraphic path, a visible scientific path, based on a EMCCD camera, has been implemented. Benefiting from both AO correction and new data processing techniques, it is a powerful tool for high angular resolution imaging and opens numerous new science opportunities. A factor 2 to 3 in Strehl ratio is obtained compared to the AO long exposure time: up to 25% Strehl in the 650nm wavelength, depending on the image processing algorithm used and the seeing conditions. The system is able to deliver diffraction limited images at 650 nm (17 mas FWHM). Our baseline image processing algorithm is based on the selection of the best signal for each spatial frequency. We demonstrate that this approach offers significantly better results than the classical select, shift and add approach (lucky imaging). We report on the first on-sky visible imaging results.
We also describe how the SCExAO visible channel will also later host a high performance optical wavefront sensor based on a nonlinear curvature scheme.
The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system is an instrument designed to be inserted between the Subaru AO188 system and the infrared HiCIAO camera in order to greatly improve the contrast in the very close (less than 0.5") neighbourhood of stars.
Next to the infrared coronagraphic path, a visible scientific path, based on a EMCCD camera, has been implemented. Benefiting from both AO correction and new data processing techniques, it is a powerful tool for high angular resolution imaging and opens numerous new science opportunities. A factor 2 to 3 in Strehl ratio is obtained compared to the AO long exposure time: up to 25% Strehl in the 650nm wavelength, depending on the image processing algorithm used and the seeing conditions. The system is able to deliver diffraction limited images at 650 nm (17 mas FWHM). Our baseline image processing algorithm is based on the selection of the best signal for each spatial frequency. We demonstrate that this approach offers significantly better results than the classical select, shift and add approach (lucky imaging). We report on the first on-sky visible imaging results.
We also describe how the SCExAO visible channel will also later host a high performance optical wavefront sensor based on a nonlinear curvature scheme.
No comments:
Post a Comment