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ESPRESSO Coudé-Train: ESO's VLT working as 16-metre telescope

A. Cabral, M. Abreu, J. Coelho, G. Avila, M. Riva, D. Megevand, N. C. Santos, F. Pepe

ESPRESSO is a fibre-fed, cross-dispersed, high-resolution, echelle spectrograph developed to fully exploit the European Southern Observatory VLT (Very Large Telescope), and it was open to the astronomical community at the end of 2018. This spectrograph was installed at the Combined Coudé Laboratory (CCL) of the VLT, fed by four Coudé Trains, which bring the light to the CCL from the Nasmyth platforms of the four 8.2-metre Unit Telescopes. With all four Telescopes combining their light-collecting power to feed a single instrument, the ESPRESSO Coudé Train effectively transforms the VLT into the largest optical telescope in the world in terms of collecting area. The Coudé Train is composed of a set of prisms and lenses delivering a pupil and an image to the CCL, up to 70 m away, including an Atmospheric Dispersion Compensator. The use of only refractive optics, namely Total Internal Reflection prisms, has the advantage of the inherent higher throughput, especially in the blue region of the spectrum. With these complex optics, ESPRESSO can either collect the light from up to all four Unit Telescopes together, or alternatively receive light from any one of the telescopes independently, allowing for more flexible usage of observing time. In this paper, we present the ESPRESSO Coudé Train concept, the design and the implementation on the VLT.

coudé optics, optical design, telescopes

Fourth International Conference on Applications of Optics and Photonics
Manuel Filipe P. C. M. Martins Costa

Proceedings of the SPIE
Volume 11207, Page 186
2019 October

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Faculdade de Ciências da Universidade de Lisboa Universidade do Porto Faculdade de Ciências e Tecnologia da Universidade de Coimbra
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia