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A unique, state-of-the-art array of detectors is being developed as part of AIRES, the airborne infrared echelle spectrometer for SOFIA (the Stratospheric Observatory for Infrared Astronomy). SOFIA is a Boeing 747 that will carry a 2.7-meter telescope to operating altitudes up to 45,000 feet. It is under development by NASA and the DLR (the German aerospace center). SOFIA is scheduled to begin operations at Ames Research Center in late 2004. AIRES--which is being built at Ames--is the facility spectrometer for SOFIA; it will measure atomic and molecular spectral lines at far-infrared wavelengths, approximately 30 to 400 times the wavelengths of visible light, to probe physical characteristics of astronomical sources such as star-forming regions and our galactic center.
Highlights of the AIRES detector development include the following: Infrared light collected by the SOFIA telescope will be distributed by the optical system of AIRES to its semiconductor detectors so as to permit simultaneous separation of different wavelengths in each of 24 imaging picture elements (pixels) viewing the sky. The detectors will be arranged in a 16 x 24 rectangular grid with pixels spaced eight-hundredths of an inch apart. Each detector is a chip of antimony-doped germa-nium mounted in an integrating cavity and fed with light from the spectrometer by a conical light collector, shown in figure 1.
The AIRES optical system and detector assembly will be cooled in a cryostat to a few degrees kelvin, as required to achieve the highest possible sensitivity to the infrared radiation collected by the SOFIA telescope. The detectors convert the light from the spectrometer into electrical signals, which are amplified and multiplexed by adjacent inte-grated circuits that route the signals to the data system outside the cryostat.
These unique multiplexing amplifiers were designed specifically for AIRES by industrial specialists collaborating with AIRES team members. The device technology was origi-nally developed for the Space Infrared Telescope Facility, but the new circuits are tailored for the wider range of infrared backgrounds expected on SOFIA. They feature externally programmable gains to accommodate different observing conditions, and so will be suitable for a variety of SOFIA instruments as well as some spaceborne instruments. The AIRES team pioneered this development, and has tested several devices, confirming that their cryogenic noise and gain performance meets AIRES needs.
The entire detector package--detectors, amplifiers, and array assembly--is custom designed and built, with much of the work done at Ames by the AIRES team. In previous tests, the detector configuration sketched in figure 1 was shown to work well. During FY00, testing of the amplifiers and design and fabrication of a 2 x 24 protoflight detector module have made great progress. This unique detector system, essential for the success of AIRES, is well on its way to achieving its design performance.
Point of Contact: E. Erickson
(650) 604-5508
erickson@cygnus.arc.nasa.gov
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Fig. 1. Detail of the AIRES far-infrared detector geometry.
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