15 September 2011 FUV quantum efficiency degradation of cesium iodide photocathodes caused by exposure to thermal atomic oxygen
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Abstract
The color dependence of the measured decline of the on-orbit sensitivity of the FUV channel of the HST Cosmic Origins Spectrograph (HST-COS) indicated the principal loss mechanism to be degradation of the cesium iodide (CsI) photocathode of the open-faced FUV detector. A possible cause of this degradation is contamination by atomic oxygen (AO), prompting an investigation of the interaction of AO with CsI. To address this question, opaque CsI photocathodes were deposited on stainless steel substrates employing the same deposition techniques and parameters used for the photocathodes of the HST-COS FUV detector. The as-deposited FUV quantum efficiency of these photocathodes was measured in the 117-174 nm range. Several of the photocathodes were exposed to varying levels of thermalized, atomic oxygen (AO) fluence (produced via an RF plasma). The post AO exposure QE's were measured and the degradation of sensitivity versus wavelength and AO fluence are presented.
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Jason McPhate, Joshi Anne, John Bacinski, Bruce Banks, Carey Cates, Paul Christensen, Brett Cruden, Larry Dunham, Eric Graham, David Hughes, Randy Kimble, Olivia Lupie, Malcolm Niedner, Steven Osterman, Steven Penton, Charles Proffitt, Diane Pugel, Oswald Siegmund, Thomas Wheeler, "FUV quantum efficiency degradation of cesium iodide photocathodes caused by exposure to thermal atomic oxygen", Proc. SPIE 8145, UV, X-Ray, and Gamma-Ray Space Instrumentation for Astronomy XVII, 81450I (15 September 2011); doi: 10.1117/12.897024; https://doi.org/10.1117/12.897024
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