GREST (Getting Ready for EST) was a European initiative for the development of new sensor and detector technologies for the European Solar Telescope (EST). EST (for an artistic illustration see figure 1) is one of the next generation solar telescopes and supposed to start operation in 2030 . Among other objectives, EST will perform time resolved, high precision polarimetric imaging.
The magnetic fields within the solar atmosphere cause the polarization of the Suns light. Precise measurements of the polarization allow infer the magnetic fields within the solar atmosphere. Time resolved polarimetry furthermore, allows observation of the interplay of magnetic fields with e.g. the plasma flow and other the physical processes in the solar atmosphere.
The principle of time-resolved polarimetry is illustrated in figure 2. The incident light passes through a modulator followed by a linear polarizer. This translates the polarization of the incident light into an intensity modulation. The intensity modulation is recorded by a suitable detector, that is synchronized to the modulator. From the recorded intensity modulation, the polarization of the incident light can be determined. In the illustration, the modulator has only two distinct states. For high precision polarimetry, four different intensity modulation states are recorded. This requires a sensor with four distinct storages.
For this purpose the MPG-HLL developed two DePFET based sensor concepts, the Central Anode and the Quadropix DePFET . A Quadropix consists of four DePFETs within one superpixel structure (see figure 3 and “Link to Quadropix”). In the context of GREST we demonstrated the functionality of the Quadropix and further its suitability as sensor element for a high precision polarimetric imaging camera.
Artistic impression of the European Solar Telescope
Principle of time resolved precision polarimetric imaging
A Quadropix consists of four DePFETs
1)S. A. Matthews et al. “The European Solar Telescope”. In: Proc. SPIE 9908.990809 (2016). DOI: http://dx.doi. org/10.1117/12.2234145
2)Alexander Baehr et al. “Advanced DePFET Concepts: Quadropix”. In: NIM-A (2017). DOI: https://doi.org/10. 1016/j.nima.2017.10.048.