Linestrength ratio spectroscopy as a new primary thermometer for redefined Kelvin dissemination

Abstract

Experimental methods for primary thermometry, after Kelvin unit redefinition on May 2019, become based on a known value of the Boltzmann constant rather than by measuring temperature with respect to a reference point. In this frame, we propose linestrength ratio thermometry (LRT) as a candidate method for primary thermometry in the 9-700 K temperature range. Temperature accuracies at the ppm level are prospected for LRT applied to optical transitions of the CO molecule in the range 80-700 K and of a rare-earth-doped crystal in the 9-100 K one. Future implementations of this technique can contribute to measure the calibration-discrepancies in the ITS-90 metrological scale of thermodynamic temperature which can have a measurable impact in applications ranging from fundamental-physics to meteorology and climatology.

Laser-Based Primary Thermometry: A Review

“…which ultimately depends only on the temperature 𝑇 to be determined if 𝑇 𝑅𝐸𝐹 is precisely known [93][94]. The strength of the approach is that 𝐹(𝑇, 𝑇 𝑅𝐸𝐹 ) does not depend on the partition function 𝑄(𝑇), which is then excluded from the error budget, and can be computed by the ratio of numerically integrated absorbances, thereby circumventing also the line-shape hurdle.…”

“…The strength of the approach is that 𝐹(𝑇, 𝑇 𝑅𝐸𝐹 ) does not depend on the partition function 𝑄(𝑇), which is then excluded from the error budget, and can be computed by the ratio of numerically integrated absorbances, thereby circumventing also the line-shape hurdle. Although no experimental validation of LRT has been reported yet, simulations predict accuracies at the ppm level or even below for optical transitions of carbon monoxide (CO) around 4200 cm -1 in the temperature range 80-700 K [93][94].…”

“…One of these experiments is DBT applied to an intercombination line of Hg in the UV [78][79][80], which promises to break the current Cs benchmark on atomic substances, also thanks to a particularly small vapor pressure at TPW. A second experiment which should provide a 1-ppm-level accuracy with large insensitivity to line-shape issues is LRT, which is planned to be applied to two CO transitions around 4200 cm -1 in the 80-700 K temperature range [94].…”