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Cell-based refractometer for pascal realization.

Patrick F Egan, Jack A Stone, Jacob E Ricker

    Optics Letters
    |September 29, 2017
    PubMed
    Summary
    This summary is machine-generated.

    We developed a new method using helium refractivity to determine density and realize the pascal. This technique also allowed us to measure the Boltzmann constant with high accuracy.

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    Area of Science:

    • Metrology and fundamental physical constants
    • Optical physics and interferometry
    • Thermodynamics and gas properties

    Background:

    • Accurate determination of physical constants like the Boltzmann constant is crucial for scientific advancement.
    • Realizing fundamental units such as the pascal requires precise measurements of gas properties.
    • Optical refractivity offers a sensitive method for probing gas density.

    Purpose of the Study:

    • To establish a novel method for determining helium density using optical refractivity measurements.
    • To realize the pascal unit of pressure through precise density determination.
    • To measure the Boltzmann constant with high accuracy by leveraging helium refractivity.

    Main Methods:

    • Utilizing a quasi-monolithic heterodyne interferometer integrated with a gas triple-cell for high-stability measurements.
    • Implementing a method to cancel pathlength uncertainty caused by cell window thinning.
    • Measuring helium refractivity at precisely controlled temperature and pressure conditions.

    Main Results:

    • Achieved high stability of ±50 pm over 10 hours in the interferometer.
    • Quantified and canceled cell window thinning effects to a fractional error of 9.3×10⁻⁶ in helium refractivity.
    • Reported the ratio of nitrogen to helium refractivity as 8.570354(13).

    Conclusions:

    • The developed method allows for accurate determination of helium density and realization of the pascal.
    • The measurement of helium refractivity provides a new pathway for determining the Boltzmann constant.
    • The reported refractivity ratio can be used for calibrating other refractometers.