Laser guide star pointing camera for ESO LGS Facilities

D. Bonaccini Calia; M. Centrone; F. Pedichini; A. Ricciardi; A. Cerruto; F. Ambrosino

doi:10.1117/12.2057201

7 August 2014 Laser guide star pointing camera for ESO LGS Facilities

D. Bonaccini Calia, M. Centrone, F. Pedichini, A. Ricciardi, A. Cerruto, F. Ambrosino

Proceedings Volume 9148, Adaptive Optics Systems IV; 91483P (2014) https://doi.org/10.1117/12.2057201
Event: SPIE Astronomical Telescopes + Instrumentation, 2014, Montréal, Quebec, Canada

Abstract

Every observatory using LGS-AO routinely has the experience of the long time needed to bring and acquire the laser guide star in the wavefront sensor field of view. This is mostly due to the difficulty of creating LGS pointing models, because of the opto-mechanical flexures and hysteresis in the launch and receiver telescope structures. The launch telescopes are normally sitting on the mechanical structure of the larger receiver telescope. The LGS acquisition time is even longer in case of multiple LGS systems. In this framework the optimization of the LGS systems absolute pointing accuracy is relevant to boost the time efficiency of both science and technical observations. In this paper we show the rationale, the design and the feasibility tests of a LGS Pointing Camera (LPC), which has been conceived for the VLT Adaptive Optics Facility 4LGSF project. The LPC would assist in pointing the four LGS, while the VLT is doing the initial active optics cycles to adjust its own optics on a natural star target, after a preset. The LPC allows minimizing the needed accuracy for LGS pointing model calibrations, while allowing to reach sub-arcsec LGS absolute pointing accuracy. This considerably reduces the LGS acquisition time and observations operation overheads. The LPC is a smart CCD camera, fed by a 150mm diameter aperture of a Maksutov telescope, mounted on the top ring of the VLT UT4, running Linux and acting as server for the client 4LGSF. The smart camera is able to recognize within few seconds the sky field using astrometric software, determining the stars and the LGS absolute positions. Upon request it returns the offsets to give to the LGS, to position them at the required sky coordinates. As byproduct goal, once calibrated the LPC can calculate upon request for each LGS, its return flux, its fwhm and the uplink beam scattering levels.

Citation Download Citation

D. Bonaccini Calia, M. Centrone, F. Pedichini, A. Ricciardi, A. Cerruto, and F. Ambrosino "Laser guide star pointing camera for ESO LGS Facilities", Proc. SPIE 9148, Adaptive Optics Systems IV, 91483P (7 August 2014); https://doi.org/10.1117/12.2057201

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