Deployable Doppler Thermometry

Summary

The Deployable Doppler Thermometry project strives to create portable, primary thermometers for dissemination of the kelvin from 300 K to 700 K. Our approach combines recent advances in vapor cell microfabrication and optical frequency comb metrology, which allow primary thermometers with size and measurement speed sufficient for end users. The thermometers we develop can serve as on-site references and process controllers to reduce calibration costs and improve resilience in industrial manufacturing.

Description

Accurate temperature measurements are essential to many industrial processes, including petrochemical or pharmaceutical production and nuclear power generation. Typical process control thermometers, such as resistance temperature detectors, are known to drift over time and degrade when subject to harsh environments. As a result, long and costly calibration chains are needed to ensure industrial efficiency and safety through traceability to SI units.

Illustration of Doppler thermometry. The transmission of laser light through an atomic gas depends on the atomic velocity distribution due to the Doppler effect. The Doppler-broadened width of the detected transmission dip yields the gas temperature T.

Credit: Sean Kelley/NIST

We are developing compact, calibration-free thermometers based on the Doppler effect in atomic gases. Because of the Doppler effect, the frequency of light absorbed by an atom or molecule depends on its velocity. In thermal equilibrium, the velocities of atoms in a gas follow the Boltzmann distribution, leading to Doppler-induced spectral line broadening. By measuring the Doppler broadening we can relate the gas temperature to SI-defining physical constants and immutable atomic properties, allowing for calibration-free thermometry.

To reach the thermometer size and measurement speed necessary for industrial applications, we are building Doppler thermometers using tunable optical frequency combs and microfabricated atomic vapor cells. Optical frequency combs can be used to record and average atomic spectra much more rapidly than traditional laser scanning approaches. Microfabricated atomic vapor cells maintain significant spectroscopic absorption at sizes comparable to resistance temperature detectors, due to the strong absorption of atomic gases. Applying these two technologies to Doppler thermometry will allow us to produce primary thermometers that can be straightforwardly integrated into industrial processes and calibration architectures.

Opportunities: If you are interested in joining our project as a postdoctoral researcher, guest researcher, collaborator, or student, reach out to our technical contacts.