New techniques in ultraviolet astronomical polarimetry: Wide-field imaging and far-ultraviolet spectropolarimetry

Two sounding rocket payloads under development at the Space Astronomy Laboratory are intended to explore different forms of ultraviolet astronomical polarimetry as a follow-up to the successful mission of the Wisconsin Ultraviolet Photo-Polarimeter Experiment ("WUPPE"). The unknown territory of diffuse-object ultraviolet polarimetry is to be explored by the Wide-Field Imaging Survey Polarimeter ("WISP"). WISP is a quite unusual integrated fast telescope/polarimeter optimized for the wavelengths 1 35-260 nm. The telescope is a 19.5 cm f/1.9 all-reflective Schmidt; the first element is a large rotatable waveplate constructed of 10 cm panes of CaF2, which are made birefringent by linear pneumatic actuators along two edges. Preceding the telescope primary is a large Brewster-angle polarizing mirror which makes use of a high-index opaque monolayer. The detector is a UV-sensitized CCD. This instrument will be used to obtain ultraviolet polarimetric images of starlight scattered from diffuse galactic dust clouds over a 1.7x5 ° field of view with 15 arcsec resolution. The first WISP flight is scheduled for Fall 1993, targeting the Pleiades reflection nebula. Just in its early development is another sounding rocket payload, the Far-Ultraviolet Spectropolarimeter ("FUSP"). This instrument is to have a resolution of better than 0.1 nm and a spectral coverage from 105 to 145 nm. It will consist of a 0.4m parabolic primary with polarimetric optics at the prime focus and a far ultraviolet spectrometer. The polarimetric analyzer will be a thin stressed-L1F waveplate, followed by a diamond Brewster-angle polarizer. 1