Multi Conjugate Adaptive Optics Demonstrator, Layer Oriented WFS Final Design

Date Issued
2003
Author(s)
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Viard, Elise
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Carbillet, Marcel
Abstract
The ESO Multi-Conjugate Adaptive Optics Demonstrator (MAD) has been identified as an essential component to demonstrate on sky MCAO techniques, both for the OWL 100-m telescope concept and for the ESO VLT 2nd Generation instrumentation. MAD is intended to be a Multi-Conjugate Adaptive Optics prototype to be tested at VLT. It is conceived as a fast track project by re-using as much as possible key components developed in the scope of existing VLT AO systems. The WFS area has 2 channels: a Shack-Hartmann based one for the star oriented configuration and a Pyramid based one for the Layer-Oriented configuration. The scope of this document is to provide the final design of the Layer-Oriented wavefront sensor. The LOWFS is based upon multi-pyramid wavefront sensing. The light coming from several references (a maximum of 8 in the MAD case) can be collected by 8 star enlargers, which are optical systems with the purpose to increase individually the stars dimensions without changing the distances. Each enlarged star image is then split by a pyramid and the four spot coming from the 8 pyramids are re-imaged by an objective on a CCD detector; in case that the detector is conjugated to the pupil plane (i.e. focused on the ground) the 4 pupils coming from each pyramid are superimposed, thus increasing uniformly the SNR of the system, while if the detector plane is conjugated to a different altitude, there is a partial overlapping of the pupil images coming from the different references, generating what is called “metapupil”. The shape of this metapupil depends upon the geometry of the considered asterism, i.e. the position of the references in the field; the superimposition area also depends on the asterism geometry and additionally on the conjugation altitude (the higher the altitude the lower the superimposition). The details concerning the optical and mechanical design of the LOWFS, together with the selected components list and with the Hazard Analysis, are presented in this document.
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OWL-TRE-INA-60000-0055
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T2-TechRep-OWL-TRE-INA-60000-0055-MAD-LO_WFS_FinalDesign.pdf

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