MEASURING PRESSURE AND VACUUM WITH LIGHT: A NEW PHOTONIC, QUANTUM-BASED, PRESSURE STANDARD
Jay H. Hendricks, Jacob E. Ricker, Jack A. Stone Jr., Patrick F. Egan, Gregory E. Scace, Gregory F. Strouse, Douglas A. Olson, Donavon Gerty
The future of pressure and vacuum measurement will rely on lasers and Fabry-Perot optical cavities, and will be based on fundamental physics of light interacting with a gas. Light interacts at the quantum level with matter such that light travels at a slower speed and has shorter wavelength in gas than it does in vacuum. A photonic-based pressure standard represents a disruptive change in the way of realizing and disseminating the SI unit of pressure, the pascal. The underlying metrology behind the advance is the ultra-accurate determination of the refractive index of a gas by picometer optical interferometry. The aim of the project is a new technique that will improve accuracy and enable the complete replacement of all mercury-based pressure standards. The National Institute of Standards and Technology (NIST) has now built a working prototype of a fixed length optical cavity (FLOC) with impressive preliminary results. NIST is also developing an even more accurate variable length optical cavity (VLOC) that will make simultaneous ultra-precise measurements of vacuum and gas cavity optical lengths. The early results from the FLOC have exceeded first experimental expectations in that the photonic-based standard is fast, sensitive, accurate, and wide range. Early results show that resolution = 0.1 mPa (7.5x10^-7 Torr) and outperforms the NIST ultrasonic interferometer manometer with 35X improvement. The lowest pressure measured is 10X more sensitive (1 mPa vs. 10 mPa). Accuracy of the photonic based pressure standard varies between 0.02 parts in 100 (%) at medium vacuum (1 kPa) to 35 parts in 10^6 (ppm) at atmospheric pressure (100 kPa), with repeatability of 5 parts in 10^6 (ppm) or better, indicating that the standard, once fully developed, will effectively replace mercury manometers for the barometric pressure range, providing improved functionality without the associated hazards of mercury.
August 30-September 3, 2015
XXI IMEKO World Congress Measurement in Research and Industry