Stepper motors at LHe temperatures in astronomical mid-infrared instrumentation

Details Stepper motors at LHe temperatures in astronomical mid-infrared instrumentation Stepper motors at LHe temperatures in astronomical mid-infrared instrumentation

Sep 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999spie.3786..376t&link_type=abstract

Proc. SPIE Vol. 3786, p. 376-383, Optomechanical Engineering and Vibration Control, Eddy A. Derby; Colin G. Gordon; Daniel Vukob

Physics

Optics

Cryogenic, Lhe, Polarimetry, Stepper Motor, Liquid Helium, Infrared

Scientific paper

The University of Denver is now completing construction of a mid-infrared imaging polarimeter dubbed TNTCAM Mark II. The instrument will be the only one of its kind capable of attaining polarimetric accuracy of 0.2 % across the 5 -- 25 micron spectral interval. This sensitivity is only attainable by cooling the transmissive polarizing optics to liquid helium (LHe) temperatures. A major technical challenge in the design of this instrument has been finding a way to modulate the polarization signature of the incoming beam at a rate sufficient to combat the degrading effects of the atmosphere. Our group has chosen to quickly rotate a half-waveplate situated on the cold (i.e. 4 degrees Kelvin) work-surface. The waveplate is rotated between two fixed positions separated by 45 degrees at a rate of 1 Hz to obtain one of the two Stoke's parameters required to measure linear polarization. The waveplate is then offset by 22.5 degrees and then rotated again at 1 Hz between two positions separated by 45 degrees to obtain the other Stoke's parameter. In addition to rotating the waveplate, the waveplate itself must be moved out of the beam during normal imaging applications. The camera can contribute to the understanding of YSOs and evolved stars, obtaining high resolution mid-IR observations of dusty environments immediately surrounding these objects. In imaging mode mosaics of extended objects can be made in 2'x2' sub-fields. In polarimetry mode, B-fields in YSOs can be probed by dust emission from hot cores, incidentally constraining grain alignment scenarios in young stellar environments. In this paper we present the design and the results of our moving optical componenets susbsytem. Five cryo-stepper motors drive these mechanisms. This instrument is being developed under NSF grant AST-9724506 and is slated for community access in January 2000.

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