Design and fabrication of the all-reflecting H-Lyman alpha coronagraph/polarimeter

摘要

Abstract: We have designed, analyzed, and are now fabricating an All-Reflecting H-Lyman $alpha Coronagraph/Polarimeter for solar research. This new instrument operates in a narrow bandpass centered at $lambda 1215.7 angstroms - the neutral hydrogen Lyman $alpha (Ly- $alpha@) line. It is shorter and faster than the telescope which produced solar Ly-$alpha images as a part of the MSSTA payload that was launched on May 13, 1991. The Ly-$alpha is produced and linearly polarized in the solar corona by resonance scattering, and the presence of a magnetic field modifies this polarization according to the Hanle effect. The Lyman $alpha Coronagraph/Polarimeter instrument has been designed to measure coronal magnetic fields by interpreting, via the Hanle effect, the measured linear polarization of the coronal Ly-$alpha line. Ultrasmooth mirrors, polarizers, and filters are being flow-polished for this instrument from CVD silicon carbide substrates. These optical components will be coated using advanced induced transmission and absorption thin film multilayer coatings, to optimize the reflectivity and polarization properties at 1215.7 angstroms. We describe some of the solar imaging results obtained with the MSSTA Lyman $alpha coronagraph. We also discuss the optical design parameters and fabrication plans for the All-Reflecting H-Lyman $alpha Coronagraph/Polarimeter.!32