The Short-Term Performances of Two Independent Gas Modulated Refractometers for Pressure Assessments

Abstract

Refractometry is a powerful technique for pressure assessments that, due to the recent redefinition of the SI system, also offers a new route to realizing the SI unit of pressure, the Pascal. Gas modulation refractometry (GAMOR) is a methodology that has demonstrated an outstanding ability to mitigate the influences of drifts and fluctuations, leading to long-term precision in the 10−7 region. However, its short-term performance, which is of importance for a variety of applications, has not yet been scrutinized. To assess this, we investigated the short-term performance (in terms of precision) of two similar, but independent, dual Fabry–Perot cavity refractometers utilizing the GAMOR methodology. Both systems assessed the same pressure produced by a dead weight piston gauge. That way, their short-term responses were assessed without being compromised by any pressure fluctuations produced by the piston gauge or the gas delivery system. We found that the two refractometer systems have a significantly higher degree of concordance (in the 10−8 range at 1 s) than what either of them has with the piston gauge. This shows that the refractometry systems under scrutiny are capable of assessing rapidly varying pressures (with bandwidths up to 2 Hz) with precision in the 10−8 range.

Circular Comparison of Conventional Pressure Standards Using a Transportable Optical Refractometer: Preparation and Transportation

“…This contributes to its uncertainty by 20 parts-permillion, which is on par with the uncertainties of pressure balances used in the circular comparison. Its short-term precision has been shown to be significantly better than its uncertainty, in the 1:10 8 range [4].…”

“…The refractometry system, denoted the Transportable Optical Pascal (TOP), has previously been described in detail [3], [4]. Besides a brief IMEKO 24 th TC3, 14 th TC5, 6 th TC16 and 5 th TC22 International Conference 11 -13 October 2022, Cavtat-Dubrovnik, Croatia 2 of 7…”

“…It comprises, in its interior, seven modules that contain, among other things, two lasers, fibre-optics, electronics, and a gas-handling system. The DFPC is placed on top of the rack for ease of realignment [4]. For operation, the system requires external vacuum pumps.…”

“…However, this overall design has the advantages that it makes it very easy to move around within each laboratory, and minimize the footprint of the system, which otherwise can be an issue at host laboratories. It is worth to emphasize that even though the design is far from ideal in terms of performance, it has been shown in a separate work, that, primarily due to the use of the GAMOR methodology, the TOP has an excellent stability, which for all purposes for the circular comparison is significantly better than needed [4].…”

‘Quantum-Based Realizations of the Pascal’: Status and Progress of the Empir-Project: Quantumpascal

“…The GAMOR methodology has also, thanks to its mitigation of the influence of various types of disturbances, made it possible to construct transportable systems [15], [16], [17]. A comparison between two GAMOR-based systems has demonstrated that the systems have an extraordinarily high short time precision, in the 10 -8 range [16].…”