AAS 198th Meeting, June 2001
Session 5. Ground Based Instruments and Surveys
Display, Monday, June 4, 2001, 9:20am-6:30pm, Exhibit Hall

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[5.04] The AIRES Optical Design

M. R. Haas (NASA-Ames)

AIRES (Airborne InfraRed Echelle Spectrometer) is the facility spectrometer for SOFIA (Stratospheric Observatory For Infrared Astronomy). AIRES is a long-slit (~160'') spectrometer designed to cover the 17 to 210-\mum range with good sensitivity using three spectroscopic arrays. Initially, only the 30 - 130 \mum, mid-wavelength array will be available. The instrument has a cryogenic K-mirror to perform field rotation and a slit-viewing camera (\lambda < 28 \mum, FOV = 160'' diameter) to image source morphology and verify telescope pointing.

AIRES employs a large echelle grating to achieve a spectral resolving power (\lambda /\delta \lambda) of approximately 1.0\times 106/\lambda\mu, where \lambda\mu is the wavelength in microns. Hyperfine, Inc. has ruled and tested the AIRES' echelle; its wave-front error is 0.028 waves RMS at 10.6 \mum. The instrument is housed in a liquid-helium cryostat which is constrained in diameter (~1~m) and length (~2~m) by the observatory. Hence, the length of the echelle (~1.1~m) and the focal length of its collimator (~5.2~m) severely drive the optical design and packaging.

The final design uses diamond-turned aluminum optics and has up to 19 reflections inside the cryostat, depending on the optical path. This design was generated, optimized, and toleranced using Code V. The predicted performance is nearly diffraction-limited at 17 \mum; the error budget is dominated by design residuals. Light loss due to slit rotation and slit curvature has been minimized. A thorough diffraction analysis with GLAD was used to size the mirrors and baffles; the internal light loss is shown to be a strong function of slit width.

The author(s) of this abstract have provided an email address for comments about the abstract: haas@cygnus.arc.nasa.gov

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