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Sahlmann, J.

Paper Title Page
ROAA05 An Approach to Stabilizing Large Telescopes for Stellar Interferometry 497
  • J. Sahlmann, A. Wallander, N. Di Lieto
    ESO, Garching bei Muenchen
  • G. Vasisht
    Jet Propulsion Laboratory, Pasadena, California
  In stellar interferometry fringe-tracking is a method of stabilizing the Optical Pathlength Difference (OPD) from the observed astronomical source to the instrument detector via different telescopes in an interferometric array. At the ESO VLT Interferometer, which includes four 8.2 m class Unit Telescopes (UTs), stabilization to better than a tenth of the observing wavelength is required in order to improve the quality and sensitivity of fringe measurements on the interferometer's scientific instruments. Unfortunately, fast mechanical vibrations due to myriad sources in the observatory infrastructure couple to UT support structure and propagate to the large telescope mirrors. The mirror motions are fast and large (typically about a wavelength) and must be compensated for in real time. We have implemented a scheme to measure the accelerations imparted to the primary, secondary, and tertiary mirrors of the UTs via a grid of suitably placed accelerometers. The measured accelerations, coupled with a simple geometric model, are converted to optical pathlengths and canceled by a wideband feed-forward compensation to a downstream optical delay line.  
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