Window heating effects are an important factor in development of missile seeker systems. Of specific concern are increases in window emissivity and reflectance as aerodynamic heating rapidly increases the window surface temperature. This paper describes a proposed experimental technique to measure window emissivity and reflectance over a temperature range from ambient to 350 degree(s)C and at spectral wavelengths in the 2.5 to 5.0 micron range. For this novel test setup the laser beam impinges on the infrared window sample at the Brewster angle to eliminate reflection losses so that remaining losses in laser intensity can be attributed to window emissivity. The proposed test procedures and laboratory equipment required to obtain these measurements are described in detail.
Edward F. Cross,
"Emissivity and reflectivity measurements of heated windows with a tunable laser", Proc. SPIE 2269, Infrared Technology XX, (17 October 1994); doi: 10.1117/12.188680; https://doi.org/10.1117/12.188680