9 August 2016 Commissioning the polarimetric modes of the Robert Stobie spectrograph on the Southern African Large Telescope
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The Robert Stobie Spectrograph is currently the main workhorse spectroscopic instrument on the Southern African Large Telescope (SALT), which has been undergoing regular scientific operations since 2011. The visible beam of the RSS was designed to perform polarimetry in all of its modes, imaging and grating spectroscopy (with Multi Object Spectroscopy capability) from 3200 to 9000 Å. The polarimetric field of view is 4×8 arcmin. Initial early commissioning of the polarimetric modes was stalled in 2011 because a coupling fluid leak developed in the polarizing beamsplitter after less than a year of operation. As a result, it was decided to redesign the beamsplitter to use a different optical couplant. This was complicated by the unusual thermal expansion properties of the calcite optic, and by the necessity of aligning the individual elements in the beamsplitter mosaic (RSS is the first instrument to use a mosaic beamsplitter). Laboratory work selected a new couplant: a gel, Nye 451. Testing was completed with satisfactory results on a "sacrificial" calcite prism with the same geometry as an actual mosaic element. A successful assembly was performed and the beamsplitter was re-installed in SALT in mid-2015. We describe results from the renewed commissioning efforts to characterize polarimetry from SALT and include some early performance verification science.
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S. B. Potter, S. B. Potter, Ken Nordsieck, Ken Nordsieck, Encarni Romero-Colmenero, Encarni Romero-Colmenero, Steve Crawford, Steve Crawford, Petri Vaisanen, Petri Vaisanen, Éric Depagne, Éric Depagne, David Buckley, David Buckley, Anthony Koeslag, Anthony Koeslag, Janus Brink, Janus Brink, Christian Hetlage, Christian Hetlage, Keith Browne, Keith Browne, Lisa Crause, Lisa Crause, Alan Schier, Alan Schier, James Allington, James Allington, } "Commissioning the polarimetric modes of the Robert Stobie spectrograph on the Southern African Large Telescope", Proc. SPIE 9908, Ground-based and Airborne Instrumentation for Astronomy VI, 99082K (9 August 2016); doi: 10.1117/12.2232391; https://doi.org/10.1117/12.2232391

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