COALA (COphasing and ALignment Aid) is an instrument aimed to measure the relative alignment and piston of any three adjacent segments of the primary mirror of the GTC during day without using stellar light. The main driver in conceiving COALA has been the increase overall operation efficiency of GTC permitting to recover the telescope alignment after exchanging recoated segments without the constraints of weather and seeing conditions imposed by the current alignment/phasing procedures using focal plane WFS illuminated with stellar light. This instrument is a 6 sub-apertures wavefront sensor built around a Ø350mm telescope. Three sub apertures are used to measured tip-tilt between segments as in a Shack-Hartmann WFS. The other three sub-apertures include chromatic dispersion prisms that permit to measure a chromatically dispersed diffraction image of apertures placed between segments, the analysis of that images permits to measure the relative piston between segments within 8μm range without ambiguity. For using the instrument, a quasi-punctual white light source is placed in the telescope focus to generate a collimated beam. COALA analyze the wavefront of that collimated beam generated by the telescope. COALA is attached to the telescope dome in an alt-azimuthal mount. Combined motion of COALA and telescope mounts permit that the subapertures of COALA can scan the full aperture of the telescope without the need of an intruder mechanical system in front of the primary mirror. COALA has been installed in the GTC in October 2023, and the commissioning tasks are ongoing. This paper describes the design of the instrument and the results obtained during commissioning.
Since the beginning of the development of the Gran Telescopio Canarias (GTC), an Adaptive Optics (AO) system was considered necessary to exploit the full diffraction-limited potential of the telescope. The GTC AO system designed during the last years is based on a single deformable mirror conjugated to the telescope pupil, and a Shack-Hartmann wavefront sensor with 20 x 20 subapertures, using an OCAM2 camera. The GTCAO system will provide a corrected beam with a Strehl Ratio (SR) of 0.65 in K-band with bright natural guide stars.
Most of the subsystems have been manufactured and delivered. The upgrade for the operation with a Laser Guide Star (LGS) system has been recently approved. The present status of the GTCAO system, currently in its laboratory integration phase, is summarized in this paper.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.