Gas equilibration gas modulation refractometry for assessment of pressure with sub-ppm precision

Isak Silander, Thomas Hausmaninger, Clayton Forssén, Martin Zelan, Ove Axner

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    21 Citations (Scopus)


    Gas modulation refractometry (GAMOR) is a methodology that, by performing repeated reference assessments with the measurement cavity being evacuated while the reference cavity is held at a constant pressure, can mitigate drifts in dual Fabry-Perot cavity based refractometry. A novel realization of GAMOR, referred to as gas equilibration GAMOR, that outperforms the original realization of GAMOR, here referred to as single cavity modulated GAMOR (SCM-GAMOR), is presented. In this, the reference measurements are carried out by equalizing the pressures in the two cavities, whereby the time it takes to reach adequate conditions for the reference measurements has been reduced. This implies that a larger fraction of the measurement cycle can be devoted to data acquisition, which reduces white noise and improves on its short-term characteristics. The presented realization also encompasses a new cavity design with improved temperature stabilization and assessment. This has contributed to improved long-term characteristics of the GAMOR methodology. The system was characterized with respect to a dead weight pressure balance. It was found that the system shows a significantly improved precision with respect to SCM-GAMOR for all integration times. For a pressure of 4303 Pa, it can provide a response for short integration times (up to 10 min) of 1.5 mPa (cycle)1/2, while for longer integration times (up to 18 h), it shows an integration time-independent Allan deviation of 1 mPa (corresponding to a precision, defined as twice the Allan deviation, of 0.5 ppm), exceeding the original SCM-GAMOR system by a factor of 2 and 8, respectively. When used for low pressures, it can provide a precision in the sub-mPa region; for the case with an evacuated measurement cavity, the system provided, for up to 40 measurement cycles (ca. 1.5 h), a white noise of 0.7 mPa (cycle)1/2, and a minimum Allan deviation of 0.15 mPa. It shows a purely linear response in the 2.8-10.1 kPa range. This implies that the system can be used for the transfer of calibration over large pressure ranges with exceptional low uncertainty.

    Original languageEnglish
    Article number042901
    JournalJournal of Vacuum Science and Technology B: Nanotechnology and Microelectronics
    Issue number4
    Publication statusPublished - 2019
    MoE publication typeA1 Journal article-refereed


    This research was in part supported by the EMPIR initiative (No. 14IND06), which is cofounded by the European Union’s Horizon 2020 research and innovation program and the EMPIR Participating States; the Swedish Research Council (VR), Project No. 621-2015-04374; the Umeå University Industrial doctoral school (IDS); the Vinnova Metrology Programme, Project Nos. 2015-0647 and 2014-06095; and the Kempe Foundations, Project No. 1823, U12.


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