Towards an improved helium-based refractometer for pressure measurements

Abstract

This paper describes a quantum realization of the pascal based a helium absolute refractometer at 532 nm. The short-term stability in pressure is ± 2 mPa with a resolution in pressure of this new optical pressure standard is better than 1 mPa with temperature stability about 1 mK. A new design of the refractometer is presented to have better temperature stability and accurate temperature measurements to reach uncertainties in pressure better than current conventional methods.

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

“…These exciting prospects have spurred a significant increase of interest within the field of refractometry. Work to explore and utilize the potential of optical methods for assessing the molar density and pressure of gas presently takes place at several national metrology institutes and universities [ 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 ].…”

“…The best performing refractometers are based on Fabry–Perot (FP) cavities, where a laser is used to probe the frequency of a longitudinal cavity mode [ 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 ]. By measuring the change in frequency between an empty (evacuated) and a gas-filled cavity, the refractivity can be assessed, from which the molar density and the pressure can be calculated.…”

“…As was alluded to above, to make viable assessments of large pressure shifts with short settling times, which is needed for a number of applications, it is of importance that the system has a fast response. Although several types of refractometers have been scrutinized over the years [ 3 , 4 , 5 , 6 , 7 , 8 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 24 , 25 , 26 ], virtually none of them has yet been assessed with respect to its short-term behavior. Access to two GAMOR-based refractometer systems allows for scrutiny of the short-term behavior of GAMOR-based refractometry in more detail.…”

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

“…This is addressed firstly by developing a means of stabilising the temperature of the cavity spacer (so as to minimising its gradients), and secondly by developing methods for absolute and traceable temperature determinations. Systems based on Pt-100s, classical thermistors, or the melting point of Ga have been developed that either use resonators made of Invar, in which there are minimal thermal gradients (see below) [7], or Zerodur, where most of the gas under investigation is in direct contact with thermalized copper surfaces [8]. Additionally, utilizing a FP spacer made from sapphire the feasibility of high-resolution photonic thermometry for temperature control will be investigated, of which the first results will be presented by Molto et al in [9].…”

Measurements of helium permeation in Zerodur glass used for the realisation of quantum pascal

“…Consequently, at low pressures, pascal is realized through the law of ideal gases, utilizing the optical measurement of gas density [3]. One of the methods that serves for the latter purpose, relies on Fabry-Perot optical cavities for the measurement of refractivity of the gas being used [4], [5].…”