QuantumPascal Report D1 Fabry-Perot-cavity-based refractometry — A guide to its realization and implementation

The present report constitutes the D1 report addressed to EURAMET of the first work package ”Pressure measurements based on Fabry-Pérot cavity based refractometry” of the EMPIR 18SIB04 ”QuantumPascal” project, titled ”Towards quantum-based realisations of the pascal”. Its aim is to, based on four guides, viz. those on Cavity deformation from A1.1.4, Temperature control and assessment from A1.2.3, Gas permeation from A1.3.4, and Gas modulation methodologies from A1.4.3, provide a ”Design guide for FP-based refractometry for pressure assessments with relative uncertainties of 500 ppm in the range 1 Pa – 1 kPa and 10 ppm in the range 1 kPa - 100 kPa”. Based on the four guides, the report adequately presents the outcome of the ”QuantumPascal” project within the aforementioned areas. Significant progress has been achieved within all of these areas. Regarding cavity deformation, a novel methodology for assessment of the cavity deformation that, for the case when pure gases are used, can provide such an accurate assessment that the deformation only contributes to the uncertainty in the assessment of pressure down on the 1 - 2 ppm level. Several systems have been realized that can provide assessments of the gas temperature with such low uncertainty that are well below the requirement for obtaining the benchmark conditions. Studies of gas permeability have been made that clearly provide recommendations for which cavity spacer materials are suitable and which should be avoided. The Gas Modulation Refractometry (GAMOR) methodology has been further developed so as to make possible assessments of important characterization parameters with low uncertainty and to allow for the realization of refractometers with a short-term precision down to the 10−8 level and an uncertainty close to the benchmarks. It has also allowed for the construction of a transportable system that has been used in other work packages. The guide also provides an updated theoretical model of Fabry-Pérot (FP) refractometry that includes effects of frequency shifts, mode jumps, cavity deformation, mirror penetration depth, and the Gouy phase. It also provides a set of recommendations for the realization of FP cavity based refractometry.Acknowledgement: This project '18SIB04 QuantumPascal' has received funding from the EMPIR programme co-financed by the Participating States and from the European Union's Horizon 2020 research and innovation programme. More information can be found on the website: https://www.ptb.de/empir2019/quantumpascal