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12 October 2004 Angle-of-incidence effects in the spectral performance of the infrared array camera of the Spitzer Space Telescope
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The Infrared Array Camera (IRAC) on board the Spitzer Space Telescope uses two dichroic beamsplitters, four interference filters, and four detector arrays to acquire images in four different channels with nominal wavelengths of 3.6, 4.5, 5.8, and 8 μm for channels 1 through 4 respectively. A ray-tracing analysis of the IRAC optical system indicates a distribution of angles that is position-dependent at each optical element and the focal-plane arrays. For the band-pass filters in channels 1 and 2, the angle distribution relative to the filter surface normal is 0-28°, whereas for channels 3 and 4, the distribution is from 30° to 58°. Since these angle variations will cause changes in the center-band wavelengths for these interference filters that needed to be accounted for, we performed spectral performance measurements as a function of the angle of incidence on witness samples corresponding to each of the four filters and the two beamsplitters in the IRAC instrument. These measurements were done in the 2-10 μm wavelength range and at the temperature of 5 K, which is near the operating temperature of IRAC. Based on these filter measurements, we also performed an analysis of the pass-band wavelength distributions as a function of position on the instrument focal-plane array detectors. This information is necessary to attain the highest possible photometric accuracy when using IRAC for astronomical observations.
© (2004) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Manuel A. Quijada, Catherine Trout Marx, Richard G. Arendt, and Samuel Harvey Moseley "Angle-of-incidence effects in the spectral performance of the infrared array camera of the Spitzer Space Telescope", Proc. SPIE 5487, Optical, Infrared, and Millimeter Space Telescopes, (12 October 2004);


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