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Thermodynamic Metrology Group

The Thermodynamic Metrology Group realizes, maintains, and disseminates the national measurement standards for temperature, humidity, pressure, vacuum, and leaks.

The group mission is to advance the state of the art in measurement of thermodynamic quantities. We have active efforts in optics, nano-photonics, and quantum-based metrology along with traditional precision measurements to advance U.S. industry. We collaborate nationally and internationally, and engage in metrology education and outreach.

Collaboration Opportunities

We invite collaboration on joint research, technology, and standards development projects. Want to work with us? Here’s how:

Or contact a project PI directly to learn how to get involved.

Research Projects and Programs

Cold Core Technology Platform

We are building a cold-atom based sensor program that represents a new approach to metrology—to establish a set of chip-scale tools that enable real-world use

Fixed Point Development : Non-Metals

We are developing new fixed points and new maintenance systems for use with Standard Platinum Resistance Thermometers (SPRTs) below the triple point of water

Photonic Dosimetry

As part of the NIST on a Chip program, the Photonic Dosimetry project is developing in-situ sub-micrometer ionizing-radiation dosimetry and calorimetry leading

Photonic Thermometry

Resistance thermometry, a time-tested method for taking temperature measurement, relies on taking accurate temperature-dependent resistance measurement of a

Measurement Services Projects and Programs


The NIST Thermodynamic Metrology Group maintains and develops national standards of humidity (in the range 1 nmol/mol to 0.6 mol/mol of water concentration)


The NIST Thermodynamic Metrology Group (TMG) provides critical research into pressure measurement capabilities improving uncertainties in user facilities and


The NIST Thermodynamic Metrology Group maintains and develops national standards of temperature (in the range 0.65 K to 2011 K), and supports calibration of all

Archive Projects and Programs

Acoustic Thermometry

By measuring the speed of sound in argon gas, we have determined thermodynamic temperature with unprecedented accuracy in the range 0 °C to 552 °C. Our results

Dynamic Pressure

Manufacturing processes by their very nature require a judicious, time-dependent use of pressure and temperature to transform a base material into a valuable

News and Updates

Tracking Lab-Grown Tissue With Light

Someday, doctors would like to grow limbs and other body tissue for soldiers who have lost arms in battle, children who need a new heart or liver, and many


On-chip Silicon Photonics Radiation Sensors

Nikolai N. Klimov, Zeeshan Ahmed, Lonnie T. Cumberland, Ileana M. Pazos, Ronald E. Tosh, Ryan P. Fitzgerald
We have examined the impact of cobalt-60-ray radiation up to 1 megagray (MGy) absorbed dose on silicon photonic devices. We do not find any systematic impact

Patents (pending and active, not including provisional)

Triple Point Immersion Cell Article (pending), US20210072098A1. Tew & Nanninga. March 11, 2021

Deformometer for determining deformation of an optical cavity optic, US Patent 10,935,370. Ahmed, Douglass, Eckel, Egan, Hendricks, Stone. Mar 2, 2021

Deformometer for determining deformation of an optical cavity optic, US Patent 10,816,325. Ahmed, Douglass, Eckel, Hendricks, Stone. Oct 27, 2020

Photonic calorimeter and process for performing calorimetry, US Patent 10,782,421. Tosh, Ahmed, Fitzgerald, Klimov. Sep 22, 2020

Photonic dosimeter and process for performing dosimetry, US Patent 10,718,872. Tosh, Ahmed, Fitzgerald, Klimov. Jul 21, 2020

Uniaxial counter-propagating monolaser atom trap (pending), US20200120785A1. Eckel, Barker, Fedchak, Scherschligt, Norrgard, Klimov. Apr 16, 2020

High-resolution photonic thermometer article (pending), US20200103594A1. Klimov, Douglass, Ahmed. Apr 2, 2020

Photonic quantum dew point sensor (pending), US20200041431A1. Herman, Klimov, Purdy. Feb 10, 2020

Optofluidic Flow Meter, US Patent 10,151,681 B2. Ahmed & Cooksey. Dec 11, 2018

Optical temperature sensor and use of same, US Patent 9,726,553. Ahmed, Semanick, Taylor, Fan, Hafezi, Xu, Strouse. Aug 8, 2017

Tools and Instruments

Piston gauges and pressure transducers

Piston gauges are used to calibrate customer piston gauges and pressure sensing devices. Piston gauges are calibrated via a direct comparison to another piston

Low Pressure Gauges

NIST has developed best-in-the-world primary standard pressure measurement capabilities for pressures spanning the range of 0.01 Pa to 360 kPa through the

Vacuum Gauges

Most calibrations of vacuum gauges are based on a known gas flow rate that is generated by one of two flow meters that operate at constant pressure. The "piston

Leak Artifacts

Leak artifacts are calibrated in the range 1 x 10-6 to 1 x 10-13 mol/s (2 x 10-2 to 2 x 10-9 std. cm3/s at 0 °C). The calibration can be performed directly



Group Leader

Office Manager