Measurements of infrared spectral directional emittance at NIST-A status update

Abstract

Over the past two decades, the Sensor Science Division at the National Institute of Standards and Technology (NIST) has developed extensive capabilities for the characterization of the infrared optical properties of materials and components. These include the more recent development of infrared spectral emittance (emissivity) measurements by the direct method of radiance comparison to blackbody reference sources over a temperature range of 200 °C to 900 °C over a wavelength range of 2 μm to 20 μm. This paper reports on the recent progress. Initial validation of the measurement methodology was made through comparisons with the indirect method of reflectance measurement on the NIST infrared reference integrating sphere at a limited temperature range up to 200 °C. Subsequently, NIST piloted and participated in an international intercomparison of infrared spectral emittance with the national measurement institutes of France, Germany, Italy and Japan. The overall agreement of the results provides a strong validation of NIST's methodologies and uncertainty budgets. Most recently, to address the current lack of standards for total emittance, measurements are being extended to wavelengths up to 100 μm. Finally, angle-dependent emittance measurements are being implemented, which will also provide sufficient data for the calculation of hemispherical emittance.