Optical realization of the pascal—Characterization of two gas modulated refractometers

By measuring the refractivity and temperature of a gas, its pressure can be calculated from fundamental principles. The most sensitive instruments are currently based on Fabry–Perot cavities where laser is used to probe frequency cavity mode. However, for best accuracy, realization such systems requires exceptional mechanical stability. Gas modulation refractometry (GAMOR) has previously demonstrated an impressive ability mitigate influence fluctuations drifts whereby it provide high-precision (sub-ppm, i.e., sub-parts-per-million or sub- 10 − 6) assessment gas pressure. In this work, two independent GAMOR-based refractometers individually characterized, compared each other, finally calibrated dead weight piston gauge with respect their abilities assess in 4–25 kPa range. first system, referred as stationary optical pascal (SOP), uses miniature fixed point gallium cell measure temperature. second denoted transportable (TOP), relies Pt-100 sensors. expanded uncertainty ( k = 2) was estimated to, SOP TOP, [ mPa ) 2 + × 6 P ] 1 / 16 28 2, respectively. While mainly limited by molar polarizability nitrogen (8 ppm), TOP dominated (26 ppm). To verify long-term stability, were other over period 5 months. It found that all measurements fell within comparative (27 This verified error budget uncorrelated errors holds extensive time.