Design Considerations for Large Detector Arrays on Submillimeter-Wave Telescopes
The emerging technology of large (~ 10,000 pixel) submillimeter-wavebolometer arrays presents a novel optical design problem---how can such arraysbe fed by diffraction-limited telescope optics where the primary mirror is lessthan 100,000 wavelengths in diameter? Standard Cassegrain designs forradiot...
| Published in: | SPIE Proceedings, Radio Telescopes |
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| Main Author: | |
| Language: | English |
| Published: |
2000
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| Online Access: | https://doi.org/10.1117/12.390436 http://cds.cern.ch/record/429138 |
| Summary: | The emerging technology of large (~ 10,000 pixel) submillimeter-wavebolometer arrays presents a novel optical design problem---how can such arraysbe fed by diffraction-limited telescope optics where the primary mirror is lessthan 100,000 wavelengths in diameter? Standard Cassegrain designs forradiotelescope optics exhibit focal surface curvature so large that detectorscannot be placed more than 25 beam diameters from the central ray. The problemis worse for Ritchey-Cretien designs, because these minimize coma whileincreasing field curvature. Classical aberrations, including coma, are usuallydominated by diffraction in submillimeter-wave single dish telescopes. Thetelescope designer must consider (1) diffraction, (2) aberration, (3) curvatureof field, (4) cross-polarization, (5) internal reflections, (6) the effect ofblockages, (7) means of beam chopping on- and off-source, (8) gravitational andthermal deformations of the primary mirror, (9) the physical mounting of largedetector packages, and (10) the effect of gravity and (11) vibration on thosedetectors. Simultaneous optimization of these considerations in the case oflarge detector arrays leads to telescopes that differ considerably fromstandard radiotelescope designs. Offset optics provide flexibility for mountingdetectors, while eliminating blockage and internal reflections. Aberrations andcross-polarization can be the same as on-axis designs having the same diameterand focal length. Trade-offs include the complication of primary mirrorhomology and an increase in overall cost. A dramatic increase in usable fieldof view can be achieved using shaped optics. Solutions having one two sixmirrors will be discussed, including a possible six-mirror design for theproposed South Pole 10m telescope. |
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