6 October 2011 Atmospheric turbulence and high-precision ground-based solar polarimetry
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High-precision full-Stokes polarimetry at near diffraction limited spatial resolution is important to understand numerous physical processes on the Sun. In view of the next generation of ground based solar telescopes, we have explored, through numerical simulation, how polarimetric accuracy is affected by atmospheric seeing, especially in the case of large aperture telescopes with increasing ratio between mirror diameter and Fried parameter. In this work we focus on higher-order wavefront aberrations. The numerical generation of time-dependent turbulence phase screens is based on the well-known power spectral method and on the assumption that the temporal evolution is mainly caused by wind driven propagation of frozen-in turbulence across the telescope. To analyze the seeing induced cross-talk between the Stokes parameters we consider polarization modulation scheme based on a continuously rotating waveplate with rotation frequencies between 1 Hz and several 100 Hz. Further, we have started the development of a new fast solar imaging polarimeter, based on pnCCD detector technology from PNSensor. The first detector will have a size of 264 x 264 pixels and will work at frame rates of up to 1kHz, combined with a very low readout noise of 2-3 e- ENC. The camera readout electronics will allow for buffering and accumulation of images corresponding to the different phases of the fast polarization modulation. A high write-out rate (about 30 to 50 frames/s) will allow for post-facto image reconstruction. We will present the concept and the expected performance of the new polarimeter, based on the above-mentioned simulations of atmospheric seeing.
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K. Nagaraju, K. Nagaraju, A. Feller, A. Feller, S. Ihle, S. Ihle, H. Soltau, H. Soltau, } "Atmospheric turbulence and high-precision ground-based solar polarimetry", Proc. SPIE 8148, Solar Physics and Space Weather Instrumentation IV, 81480S (6 October 2011); doi: 10.1117/12.894041; https://doi.org/10.1117/12.894041

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