Design and fabrication of large spectral waveband mirror coatings for scanning Fabry-Perot etalons

Earlier publications described a novel approach to the design of mirror coatings for scanning Fabry Perot etalons[1],[2]. Since that time, we have extended the design process, fabricated mirror coatings and used them to build etalons. One design process improvement is the minimization of off-axis de-tuning. It can be significantly worse with a real mirror coating than the normal "blue shift" associated with the basic Fabry-Perot geometry. This option provides for the control of de-tuning in optimization. Another improvement is optimization for multiple-order operation of the etalon. This technique reduces etalon mirror travel while allowing tunability over a broad spectral range. The focus of this paper, however, is the experimental results obtained for coatings and etalons built for the Fine Guidance Sensor-Tunable Filter Imager (FGS-TFI) - a Canadian Space Agency funded science instrument for the James Web Space Telescope (JWST). We present measured data for both the coating and the etalon performance.