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Previous publications for the JWST-FGS-TFI instrument described the design and fabrication of mirror coatings for scanning Fabry-Perot etalons. Since that time, we have extend ed the fabrication process using ellipsometry analysis over the full operational bandwidth from 1.0 to 5.0 microns for both mirror and anti-reflection coatings. This paper will present single and multiple layer ellipsometry analysis of the a-Si/SiO 2 optical properties. Analysis improvement came from a-Si/SiO 2 interface consideration and simultaneous use of ellipsometric data from Woollam V-VASE and IR-VASE instruments. Simulations of reflectance and transmittance based on the ellipsometric analysis results will also be compared to spectrophotometric measurements for witness pieces. Keywords: Etalon, Coating, Thin-Film, amorphous Silicon, SiO 2 , Ellipsometry, Fabry-Perot Mirror 1. INTRODUCTION The James Webb Space Telescope (JWST), named in honor of the 1961-1968 NASA administrator James E. Webb, will be launched in 2014. The Canadian contribution to this international joint telescope construction, is the telescope precise star tracker named the Fine Guidance Sensor (FGS). Within the FGS, a new type of astronomical instrument camera is integrated, the Tunable Filter Imager (TFI). Since its initial design the TFI has been transformed from a dual band instrument to a single Stretched Long Wave band imager (LW-Stretched) covering the operational band from 1.6-2.5 µ m and 3.2-4.9µ m. The TFI uses a scanning Fabry-Perot cavity to select any desired wavelength within the operational waveband. The continuously adjustable Fabry-Perot cavity is described within other publications [1-2] and relies on a two silicon high flatness etalon plates coated with a thin film stack. The reflector stack is based on alternating layers of a-Si and SiO |
