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Proceedings Paper

A two-dimensional spectropolarimeter as a first-light instrument for the Daniel K. Inouye Solar Telescope
Author(s): Wolfgang Schmidt; Alexander Bell; Clemens Halbgewachs; Frank Heidecke; Thomas J. Kentischer; Oskar von der Lühe; Thomas Scheiffelen; Michael Sigwarth
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Paper Abstract

The Visible Tunable Filter (VTF) is a narrowband tunable filter system for imaging spectropolarimetry. The instrument will be one of the first-light instruments of the Daniel K. Inouye Solar Telescope (DKIST) that is currently under construction on Maui (Hawaii). The DKIST has a clear aperture of 4 meters. The VTF is being developed by the Kiepenheuer Institut für Sonnenphysik in Freiburg, as a German contribution to the DKIST. The VTF is designed as a diffraction-limited narrowband tunable instrument for Stokes spectro-polarimetry in the wavelength range between 520 and 860 nm. The instrument uses large-format Fabry-Perot interferometers (Etalons) as tunable monochromators with clear apertures of about 240 mm. To minimize the influence of gravity on the interferometer plates, the Fabry-Perots are placed horizontally. This implies a complex optical design and a three-dimensional support structure instead of a horizontal optical bench. The VTF has a field of view of one arc minute squared. With 4096x4096 pixel detectors, one pixel corresponds to an angle of 0.014” on the sky (10 x 10 km on the Sun). The spectral resolution is 6 pm at a wavelength of 600 nm. One 2Dspectrum with a polarimetric sensitivity of 5E-3 will be recorded within 13 seconds. The wavelength range of the VTF includes a number of important spectral lines for the measurement flows and magnetic fields in the atmosphere of the Sun. The VTF uses three identical large-format detectors, two for the polarimetric measurements, and one for broadband filtergrams. The main scientific observables of the VTF are Stokes polarimetric images to retrieve the magnetic field configuration of the observed area, Doppler images to measure the line-of-sight flow in the solar photosphere, and monochromatic intensity filtergrams to study higher layers of the solar atmosphere.

Paper Details

Date Published: 8 July 2014
PDF: 13 pages
Proc. SPIE 9147, Ground-based and Airborne Instrumentation for Astronomy V, 91470E (8 July 2014); doi: 10.1117/12.2056322
Show Author Affiliations
Wolfgang Schmidt, Kiepenheuer-Institut für Sonnenphysik (Germany)
Alexander Bell, Kiepenheuer-Institut für Sonnenphysik (Germany)
Clemens Halbgewachs, Kiepenheuer-Institut für Sonnenphysik (Germany)
Frank Heidecke, Kiepenheuer-Institut für Sonnenphysik (Germany)
Thomas J. Kentischer, Kiepenheuer-Institut für Sonnenphysik (Germany)
Oskar von der Lühe, Kiepenheuer-Institut für Sonnenphysik (Germany)
Thomas Scheiffelen, Kiepenheuer-Institut für Sonnenphysik (Germany)
Michael Sigwarth, Kiepenheuer-Institut für Sonnenphysik (Germany)

Published in SPIE Proceedings Vol. 9147:
Ground-based and Airborne Instrumentation for Astronomy V
Suzanne K. Ramsay; Ian S. McLean; Hideki Takami, Editor(s)

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