Raman-scattered laser guide-star photons to monitor the scatter of astronomical telescope mirrors

The first observations of laser guide-star photons that are Raman-scattered by air molecules above the Very Large Telescope (VLT) were reported in June 2017. The initial detection came from the Multi-Unit Spectroscopic Explorer (MUSE) optical integral field spectrograph, following the installation o...

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Bibliographic Details
Published in:Astronomy and astrophysics (Berlin) 2018-10, Vol.618, p.L7
Main Authors: Vogt, Frédéric P. A., Luis Álvarez, José, Bonaccini Calia, Domenico, Hackenberg, Wolfgang, Bourget, Pierre, Aranda, Ivan, Bellhouse, Callum, Blanchard, Israel, Cerda, Susana, Cid, Claudia, Comin, Mauro, Espinoza Contreras, Marcela, Hau, George, Hibon, Pascale, Holzlöhner, Ronald, Jaffé, Yara L., Kolb, Johann, Kuntschner, Harald, Madec, Pierre-Yves, Mieske, Steffen, Milli, Julien, Opitom, Cyrielle, Parraguez, Diego, Romero, Cristian, Selman, Fernando, Schmidtobreick, Linda, Smoker, Jonathan, Vera Urrutia, Sergio, Zins, Gerard
Format: Article
Language:English
Subjects:
atmospheric effects
instrumentation: adaptive optics
instrumentation: spectrographs
molecular processes
scattering
telescopes
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Summary:The first observations of laser guide-star photons that are Raman-scattered by air molecules above the Very Large Telescope (VLT) were reported in June 2017. The initial detection came from the Multi-Unit Spectroscopic Explorer (MUSE) optical integral field spectrograph, following the installation of the 4 Laser Guide Star Facility (4LGSF) on Unit Telescope 4 (UT4) of the VLT. In this Letter, we delve further into the symbiotic relationship between the 4LGSF laser guide-star system, the UT4 telescope, and MUSE by monitoring the spectral contamination of MUSE observations by Raman photons over a 27-month period. This dataset reveals that dust particles deposited on the primary and tertiary mirrors of UT4, which are responsible for a reflectivity loss of ∼8% at 6000 Å, contribute (60 ± 5)% to the laser line fluxes detected by MUSE. The flux of Raman lines, which contaminates scientific observations that are acquired with optical spectrographs, thus provides a new, non-invasive means to monitor the evolving scatter properties of the mirrors of astronomical telescopes that are equipped with laser guide-star systems.
ISSN:0004-6361
1432-0746
DOI:10.1051/0004-6361/201834135