We present an innovative concept for a new full-disk solar spectropolarimeter. The instrument is part of the new container-based Tautenburg Solar Laboratory (TauSoL), which is currently under construction and commissioning on site of the Th¨uringer Landessternwarte Tautenburg (TLS), Germany. The initial design approach is to use a single Fabry-P´erot interferometer with a 150mm clear aperture that is placed at the aperture of the solar telescope inside the container lab. In this paper, we present the current status of TauSoL and the detailed design of the light feed and the initial multi-line solar spectropolarimeter.
Laser frequency combs (LFC) provide a direct link between the radio frequency (RF) and the optical frequency
regime. The comb-like spectrum of an LFC is formed by exact equidistant laser modes, whose absolute optical
frequencies are controlled by RF-references such as atomic clocks or GPS receivers. While nowadays LFCs
are routinely used in metrological and spectroscopic fields, their application in astronomy was delayed until
recently when systems became available with a mode spacing and wavelength coverage suitable for calibration
of astronomical spectrographs. We developed a LFC based calibration system for the high-resolution echelle
spectrograph at the German Vacuum Tower Telescope (VTT), located at the Teide observatory, Tenerife, Canary
Islands. To characterize the calibration performance of the instrument, we use an all-fiber setup where sunlight
and calibration light are fed to the spectrograph by the same single-mode fiber, eliminating systematic effects
related to variable grating illumination.
The influence of thin film multilayer coatings of Fabry-Perot interferometers (FPI) on polarimetric measurements
is investigated. Because the oblique ray reflectivity of the coatings in general is polarization dependent, the
transmission profile is slightly different for the s- and p-components of light passing through the FPI, resulting
in weak artificial polarization signals. The difference increases with larger angles of incidence and higher design
reflectivity of the coatings. In order to estimate the magnitude of the effect, we perform numerical calculations
with different coating designs and different optical configurations. We conclude that while current slow focal ratio
solar FPI spectrometers are safe, high-precision polarimetric measurements with large aperture solar telescopes
which may require considerably steeper focal ratios may suffer from spurious polarization effects.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.