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7 March 2003 Imaging performance and modeling of the Infrared Multi-Object Spectrometer focal reducer
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The Infrared Multi-Object Spectrometer (IRMOS) is a facility instrument for the Kitt Peak National Observatory 4 and 2.1 meter telescopes. IRMOS is a near-IR (0.8 - 2.5 μm) spectrometer with low- to mid-resolving power (R = 300 - 3000). The IRMOS spectrometer produces simultaneous spectra of ~100 objects in its 2.8 x 2.0 arcmin field of view using a commercial MEMS multi-mirror array device (MMA) from Texas Instruments. The IRMOS optical design consists of two imaging subsystems. The focal reducer images the focal plane of the telescope onto the MMA field stop, and the spectrograph images the MMA onto the detector. We describe the breadboard subsystem alignment method and imaging performance of the focal reducer. This testing provides verification of the optomechanical alignment method and a measurement of near-angle scattered light due to mirror small-scale surface error. Interferometric measurements of subsystem wavefront error serve to verify alignment and are accomplished using a commercial, modified Twyman-Green laser unequal path interferometer. Image testing is then performed for the central field point. A mercury-argon pencil lamp provides the spectral line at 546.1 nm, and a CCD camera is the detector. We use the Optical Surface Analysis Code to predict the point-spread function and its effect on instrument slit transmission, and our breadboard test results validate this prediction. Our results show that scattered light from the subsystem and encircled energy is slightly worse than expected. Finally, we perform component level image testing of the MMA, and our results show that scattered light from the MMA is of the same magnitude as that of the focal reducer.
© (2003) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Joseph A. Connelly, Raymond G. Ohl IV, Timo T Saha, Theo Hadjimichael, John Eric Mentzell, Ronald G. Mink, Jason E Hylan, Leroy M Sparr, John Chambers, John J Hagopian, Matthew A. Greenhouse, Robert S. Winsor, and John W. MacKenty "Imaging performance and modeling of the Infrared Multi-Object Spectrometer focal reducer", Proc. SPIE 4841, Instrument Design and Performance for Optical/Infrared Ground-based Telescopes, (7 March 2003);


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