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9 August 2016 Qualification of HEIDENHAIN linear encoders for picometer resolution metrology in VTF Etalons
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The Visible Tunable Filter (VTF) is a narrowband tunable instrument for imaging spectropolarimetry in the wavelength range between 520 and 870 nm. It is based on large-format Fabry Perots with a free aperture of 250 mm. The instrument will be one of the first-light instruments of the 4 m aperture Daniel K. Inoue Solar Telescope (DKIST) that is currently under construction on Maui (Hawaii). To provide stable and repeatable spectral scanning by tuning the air gap distance of the Etalons, a metrology system with 20 pm resolution and drift stability of better 100 pm per hour is needed. The integration of the metrology system must preserve the tight optical specifications of the Etalon plates. The HEIDENHAIN LIP 382 linear encoder system has a selected linear scale for low noise high signal interpolation. The signal period is 128nm and the interpolated signal from the sensor can be read out at 128 nm/ 14 bit = 7.8125 pm. To qualify the LIP 382 system for the VTF, we investigated the resolution and stability under nominal VTF operation conditions and verified a mounting concept for the sensor heads. We present results that demonstrate that the LIP 382 system fulfills the requirements for the VTF Etalons. We also present a design for the sensor head mounts.
© (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Clemens Halbgewachs, Thomas J. Kentischer, Karsten Sändig, Joerg Baumgartner, Alexander Bell, Andreas Fischer, Stefan Funk, Frank Heidecke, Thomas Scheiffelen, Wolfgang Schmidt, Erwin Spanner, Peter Speckbacher, and Oskar F. von der Lühe "Qualification of HEIDENHAIN linear encoders for picometer resolution metrology in VTF Etalons", Proc. SPIE 9908, Ground-based and Airborne Instrumentation for Astronomy VI, 99084H (9 August 2016);


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