Abstract
We have developed a technique to measure the broadband emissivity of high reflectivity materials at cryogenic temperatures, employing a primary standard optical detector with high absorptance from visible wavelengths to beyond 200 µm. The technique has been successfully used to determine the emissivity of silver-coated stainless steel plates under development as thermal shields for the International Thermonuclear Experimental Reactor (ITER). The technique could also be useful for quantifying the low temperature emittance of coatings and components for space satellite missions, which can be essential for thermal design of these systems, especially when satellite-based detectors are dedicated to infrared measurements. In our technique, irradiance data at the detector, precise measurements of the experimental geometry, and diffraction calculations are used to determine the optical power emitted by the sample. Contact thermometry measurements for the sample can then be used to find its emissivity. Background subtraction and quantification allow determination of the directional emissivity with total absolute uncertainty (k=1) between approximately 0.0002 and 0.002 (for emissivities between 0.0035 and 0.092) over the temperature range from 80 K to 300 K.
Cryogenic Emissivity Calibration of Highly Reflective Materials
We have developed a technique to measure the broadband emissivity of high reflectivity materials at cryogenic temperatures, employing a primary standard optical detector with high absorptance from visible wavelengths to beyond 200 µm. The technique has been successfully used to determine the emissivity of silver-coated stainless steel plates under development as thermal shields for the International Thermonuclear Experimental Reactor (ITER). The technique could also be useful for quantifying the low temperature emittance of coatings and components for space satellite missions, which can be essential for thermal design of these systems, especially when satellite-based detectors are dedicated to infrared measurements. In our technique, irradiance data at the detector, precise measurements of the experimental geometry, and diffraction calculations are used to determine the optical power emitted by the sample. Contact thermometry measurements for the sample can then be used to find its emissivity. Background subtraction and quantification allow determination of the directional emissivity with total absolute uncertainty (k=1) between approximately 0.0002 and 0.002 (for emissivities between 0.0035 and 0.092) over the temperature range from 80 K to 300 K.