Electrical substitution radiometer cavity absorptance measurement

•The absorptance of a cryogenic radiometer is reported to several wavelengths.•The absorptance value uncertainty is optimized at 632.8 nm.•The developed method use cap of Teflon coatings allows high reproducibility.•The method provided the versatility to mount cavities with different geometry.

This paper presents the results of absorptance measurements of the cavity used in the cryogenic radiometer of the National Metrology Center of Mexico (CENAM) as absorptance device. The cavity absorptance was determined for several reference wavelengths in the visible range (VIS) using a He–Ne laser source and a tunable Ar–Kr laser at 476 nm, 488 nm, 520 nm, 568 nm and 676 nm. The absorptance value of 0.999 816 ± 1.9 × 10−6 (k = 2) at 632.8 nm obtained, matches with the reference value reported by the manufacturer of the cavity, L-1 Standards and Technology Inc., which is 0.999 823 ± 8.0 × 10−6 (k = 2). The variations found in the absorptance values goes from −4.4 × 10−6 to −5.1 × 10−7 for the wavelengths listed above.