Abstract
In this paper we describe new EUV/FUV (100 A < ) < 1500 A) polarimeter instrument concepts for solar research. These instruments are designed to observe linear polarization in EUV/FUV spectral lines originating in the outer solar atmosphere. Specifically: ( i) a new coronagraph/polarimeter operating at 1215.6 A (neutral hydrogen Lyman a), which could observe this line in the near solar corona and lead to the first direct measurements ofboth strength and direction of coronal magnetic fields; (ii) a new multilayer EUV imaging polarimeter, operating at the wavelengths of strong helium emission lines (e.g., 304 A, 584 A), which could observe impact polarization phenomena and provide information concerning the relative im'portance of thermal and non-thermal processes in solar flares. The emission mechanisms we will address with these instruments include resonance scattering and impact polarization. Resonance scattering of chromospheric radiation anisotropically illuminating the emitting atoms in the corona can produce up to 20% linear polarization in FUV coronal lines. Modifications, via the Hanle effect, of this polarization would result from the presence of a magnetic field. In the EUV, detectable polarization may be produced by impact polarization, which results from anisotropic collisional excitation of the emitting atoms by particles (electrons, protons) with non-Maxwellian velocity distributions produced during flares. These coronagraph/polarimeter instruments employ all-reflective optical systems utilizing ultra-smooth, low-scatter normal incidence mirrors and reflective polarization analyzers comprised of advanced flowpolished substrates with state-of-the-art thin film FUV interference and EUV multilayer coatings. The reflecting polarization analyzers operate at the Brewster angle. We discuss several instrument configurations and provide theoretical calculations and performance predictions for coronagraph/polarimeter instruments utilizing an optical design similar to the Ritchey-Chretien EUV/FUV telescopes currently being developed for flight on the Stanford/MSFC/LLNL Multi-Spectral Solar Telescope Array (MSSTA).
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