Abstract：To break through the limitations of existing pressure standards, which rely on the gravity and toxic mercury, the national metrological institutes prefer a quantum-based pressure standard. Combining the ideal gas law with helium refractivity measurement, we demonstrate a scheme for the realization of the pressure unit. The refractometer is based on a spectral interferometry with an optical frequency comb and a double-spaced vacuum cell. Through fast Fourier transform of the spectral interferograms of the two beams propagating inside and outside the vacuum cell, the helium refractivity can be obtained with a combined standard uncertainty $u(n)$ of $2.9\times 10^{-9}$. Moreover, the final $u(p)$ is $\sim$$8.7\times 10^{-6}$ in a measurement range of several megapascals (MPa). Our apparatus is compact, fast (15 ms for one single measurement) and easy to handle. Furthermore, the measurement uncertainty will be improved to $\sim$$1\times 10^{-9}$ or lower if a VIPA-based spectrometer is used. The value of $u(p)$ will thus increase to $3\times 10^{-6}$ or better in several MPa.
2018, Vol. 35 
