Broadband emissivity calibration of highly reflective samples at cryogenic temperatures

Abstract

We have developed a technique for measuring the broadband optical emissivity of high reflectivity samples at cryogenic temperatures. This measurement method employs a primary standard optical detector with high absorptance from visible wavelengths to beyond 200 µm. Background subtraction and quantification allow determination of the 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. Using the irradiance data at the detector, precise measurements of the experimental geometry and diffraction calculations, the optical power emitted by the sample can be determined. Contact thermometry measurements for the sample can then be used to find its emissivity. The emissivity calibration technique is demonstrated for large plate samples made from polished stainless steel and is also extended to calculate the separate emissivities of multiple distinct regions on a more complex sample assembly.