Emittance Measurements on Infrared Windows Exhibiting Wavelength Dependent Diffuse Transmittance

The emittance of Irtran-1 windows of thickness 1.0, 3.8, and 7.6 mm has been measured at several temperatures over the range 300°C to 700°C. The emittance of 3.8 mm standard and short wavelength Irtran-2 windows has been measured at temperatures up to 500°C. The emittance of a 3.8 mm Irtran-3 window has been measured at temperatures in the range 300°C to 850°C. A method of matching sample and blackbody temperatures has been employed which avoids the necessity of making accurate absolute temperature measurements. The applicability and sensitivity of this method is discussed. An attempt has been made to establish the effect of scattering in the samples on the measurement results.