7 September 2006 Stray light reduction in testing of NIRSpec subsystems: the focal plane array and micro-shutter assembly
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Abstract
The James Webb Space Telescope (JWST) is an infrared, space-based telescope scheduled for launch in 2013. JWST will hold four scientific instruments, including the Near Infrared Spectrograph (NIRSpec). NIRSpec operates in the wavelength range from 0.6 to 5 microns, and will be assembled by the European Space Agency. NASA/Goddard Space Flight Center (GSFC) is responsible for two NIRSpec subsystems: the detector subsystem, with the focal plane array (FPA), and the micro-shutter subsystem, with the micro-shutter assembly (MSA). The FPA consists of two side-by-side Rockwell Scientific HgCdTe 2Kx2K detectors, with the detectors and readout electronics optimized for low noise. The MSA is a GSFC developed micro-electro-mechanical system (MEMS) that serves as a programmable slit mask, allowing NIRSpec to obtain simultaneous spectra of >100 objects in a single field of view. We present the optical characterization test plan of the FPA. The test plan is driven by many requirements: cryogenic operating temperature, a flight-like beam shape, and multi-wavelength flux from 1 to 10,000 photons per second, thus low stray light is critical. We use commercial optical modeling software to predict stray light effects at the FPA. We also present the optical contrast test plan of the MSA. Each individual shutter element operates in an on/off state, and the most important optical metric is contrast. The MSA is designed to minimize stray and scattered light, and the test setup reduces stray light such that the optical contrast is measurable.
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Joseph A. Connelly, Theo J. Hadjimichael, Rene A. Boucarut, June L. Tveekrem, and D. Brent Mott "Stray light reduction in testing of NIRSpec subsystems: the focal plane array and micro-shutter assembly", Proc. SPIE 6291, Optical Systems Degradation, Contamination, and Stray Light: Effects, Measurements, and Control II, 62910V (7 September 2006); doi: 10.1117/12.678513; https://doi.org/10.1117/12.678513
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