Astron. Astrophys. Suppl. Ser. 145, 305-310

Using single-mode fibers to monitor fast Strehl ratio fluctuations

Application to a 3.6m telescope corrected by adaptive optics

V. Coudé du Foresto¹ - M. Faucherre² - N. Hubin³
- P. Gitton³

Send offprint request: V. Coudé du Foresto;
e-mail: vincent.foresto@obspm.fr

2 - Observatoire de Paris/DESPA, 5 place Jules Janssen, 92195 Meudon Cedex, France
3 - 2 rue de la chicane, 34130 Saint-Aunès, France
4 - European Southern Observatory, Karl-Schwarzschildstra$\beta$e # 2, D-85748 Garching bei München, Germany

Received September 30, 1999; accepted March 31, 2000

Abstract:

The theory of starlight coupling into single-mode fibers is reviewed to show how i) the central obstruction in a telescope pupil deteriorates coupling efficiency much more than one would expect from the loss of collecting area, and ii) a single-mode fiber and a photometer can be used to monitor fast Strehl ratio fluctuations. This last point is illustrated with experimental data obtained at the 3.6m La Silla telescope corrected with the ADONIS adaptive optics system. A 37$\times$ gain in coupling efficiency was demonstrated by turning on the adaptive optics system, but periodic fluctuations in the coupled signal revealed a vibration of the telescope tube that could not have been detected otherwise.

Key words: telescopes -- techniques: interferometric, adaptive optics -- instrumentation: large telescopes -- optical fibers: single-mode -- infrared: general