Starfire optical range long-wavelength infrared acquisition camera: initial performance report

Abstract

This paper describes installation of a long wavelength infrared (LWIR) acquisition camera on the Starfire Optical Range (SOR) 1 .5 meter telescope, and reports initial performance results. This camera was designed for acquisition of satellites night or day, irrespective of target illumination. The camera may also have wide field-of-view astronomy applications.The optical design for this LWIR acquisition camera maps a 128 x 128 pixel Si:As impurity band conduction detector array onto the two milliradian telescope scene. A warm, aspheric germanium lens images the f/217 telescope beam onto a cold field stop, and the telescope pupil onto a cryogenic chopping mirror. The cryogenic chopping mirror has an opaque mask which serves as a radiation stop. A second, cooled, aspheric germanium lens reimages the field stop onto the detector array. Operation of the camera over the 7-24 im detection band of the array is possible by replacing the interference filter and zinc selenide vacuum window.Problems and solutions pertaining to integration of the camera and cryocooler system on the telescope are described. Initial performance data reported include: optics/array radiometry, telescope background measurements, cryocooler induced telescope jitter measurements, and cryogenic chopping minor characteristics.Keywords: long wavelength infrared camera, piezoelectric actuator, cryogenic chopping minor, electrooptical sensors, LWIR imaging, celestial background 1. CAMERA DESCRIPTION Details on the design and construction of the camera are published elsewhere (LeVan, et al. 1994)1 and summarized below. The camera comprises a 128 x 128 pixel extrinsic silicon focal plane array (FPA), of impurity band conduction type, fabricated for use with high backgrounds (>3 x i0'5 photon sec1 cm2). The FPA is operated in a vacuum vessel at cryogenic temperature, with cooling achieved with a commercial Gifford-McMahon cryocooler. The second cooling stage of the cryocooler cools both the FPA and a radiation baffle containing a spectral interference filter (11.1 im < < 12.2 imFWHM) to ilK. The first stage of the cryocooler maintains the camera's radiation shields and optical components near 80K. The optical design employs a large, external germanium lens to image the f/217 telescope beam onto an 80 K field stop located behind the camera's zinc selenide vacuum window. The external germanium lens also images the telescope primary onto a chopping mirror and collocated 80K pupil 236 ISPIE Vol. 2475 0819418285/95/$6.OO Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/21/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx