Towards a dynamic pressure standard based on laser absorption spectroscopy
Kevin O. Douglass, Douglas A. Olson
We describe an approach for creating a cost-effective, field deployable dynamic pressure standard based on measurement of fundamental quantum properties of molecular systems. From the linewidth and intensities of ro-vibrational transitions we plan on making an accurate determination of pressure and temperature. The goal is to achieve an absolute uncertainty for dynamic pressure of 5 % with a measurement rate of 100 kHz. To illustrate this concept we have used wavelength modulation spectroscopy (WMS), due to inherent advantages over direct absorption spectroscopy, to perform rapid measurements of carbon dioxide in order to determine the pressure. The system records the full line shape profile of a single ro-vibrational transition of CO2 at a repetition rate of 4 kHz and with a systematic measurement uncertainty of 12 % for the linewidth measurement. A series of pressures were measured at a rate of 400 Hz (10 averages) and from these measurements the linewidth was determined with a relative uncertainty of about 0.5 % on average. The pressures measured using WMS have an average error of 0.6 % difference from the capacitance diaphragm absolute pressure sensor.