Laser refractometer as a transfer standard of the pascal

We have developed a new low pressure sensor which is based on the measurement of (nitrogen) gas refractivity inside a Fabry-Perot (FP) cavity. We compare pressure determinations via this laser refractometer to that of well-established ultrasonic manometers throughout the range 100Pa to 100000Pa. The refractometer demonstrates 10 −6 precision for p > 50 kPa; — as good or better than the manometer — we argue that a laser refractometer represents a state-of-the-art transfer standard of the pascal. We also claim the refractometer has an accuracy of U(p FP ) = [(16mPa) 2 + (11.9 × 10 −6 · p) 2 ] 1/2 , as realized through the properties of nitrogen gas.