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MUSTANG (Multiplex SQUID TES Array at Ninety GHz) is a bolometer camera for the Green Bank Telescope (GBT) working at a frequency of 90 GHz.The detector has a field of view of 40 arcsec.To cancel out random emission change from atmosphere and other sources,requires a fast scanning reflecting system with a few arcminute ranges.In this paper,the aberrations of an off-axis system are reviewed.The condition for an optimized system is provided.In an optimized system,as additional image transfer mirrors are introduced,new aberrations of the off-axis system may be reintroduced,resulting in a limited field of view.In this paper,different scanning mirror arrangements for the GBT system are analyzed through the ray tracing analysis.These include using the subreflector as the scanning mirror,chopping a flat mirror and transferring image with an ellipse mirror,and chopping a flat mirror and transferring image with a pair of face-to-face paraboloid mirrors.The system analysis shows that chopping a flat mirror and using a well aligned pair of paraboloids can generate the required field of view for the MUSTANG detector system,while other systems all suffer from larger off-axis aberrations added by the system modification.The spot diagrams of the well aligned pair of paraboloids produced are only about one Airy disk size within a scanning angle of about 3 arcmin.
MUSTANG (Multiplex SQUID TES Array at Ninety GHz) is a bolometer camera for the Green Bank Telescope (GBT) working at a frequency of 90 GHz. The detector has a field of view of 40 arcsec. Time cancel out random emission change from atmosphere and other sources, requires a fast scanning reflecting system with a few arcminute ranges.In this paper, the aberrations of an off-axis system are provided. introduced, new aberrations of the off-axis system may be reintroduced, resulting in a limited field of view.In this paper, different scanning mirror arrangements for the GBT system is analyzed through the ray tracing analysis. The include include the subreflector as the scanning mirror, chopping a flat mirror and transferred image with an ellipse mirror, and chopping a flat mirror and transferring image with a pair of face-to-face paraboloid mirrors.The system analysis shows that chopping a flat mirror and using a well aligned pair of paraboloids can generate the required field of view for the MUSTANG detector system, while other systems all suffer from larger off-axis aberrations added by the system modification. The spot diagrams of the well aligned pair of paraboloids produced are only about one Airy disk size within a scanning angle of about 3 arcmin.