Gas-refractometry-based high resolution continuous measurements in a medium vacuum

While an optical vacuum pressure standard (OVPS) using gas refractometry accurately offers a wide pressure measurement range, the measurement accuracy in the medium vacuum range is restricted by various factors. In this study, an optical vacuum pressure standard based on the refractive index measurement of gas in a Fabry-Perot (FP) cavity was developed. The measurement pressures from OVPS and the capacitance diaphragm gauge (CDG) were compared in the medium vacuum range of 4 Pa∼130 Pa. The relative differences between the two measurements ranged from 0.01 % to 0.835 %, with reproducibility relative differences ranging from 0.0323 % to 1.19 %. These results were achieved using argon gas properties. Furthermore, a high-gain, low-noise frequency measurement system based on a rubidium atomic clock frequency reference was constructed to realize the accurate measurement of beat frequency, and the argon pressure resolution was verified to be less than 5 mPa. Finally, this paper also considered the factors influencing the uncertainty of medium vacuum measurements and proposed corresponding solutions. The uncertainty of the OVPS was evaluated to be [(31 mPa)²+(77 × 10⁻⁶p)²]^1/2 (k = 2).