Abstract: We describe a new compact refractometer for air refractive index measurements. It is based on a double plane-plane Fabry Perot interferometer whose cavities of different thickness are illuminated independently by the same tunable frequency laser diode. A first one millimeter thick cavity allows unambiguous identification of the transmission peak of the second (100 mm); the laser frequency being servo- locked to the latter. This refractometer does not require any part to be evacuated during the measurement procedure. The absolute value of the refractive index of air and its fluctuations are obtained in real time by beat frequency technique combined with an optical frequency reference. Measurements provide a resolution of order 10$+$MIN@10$/ and a relative accuracy of a few times 10$+$MIN@8$/. We also describe how this refractometer is used to measure the fluctuations of the density of air used to make buoyancy corrections in mass standard comparisons. Other possible applications of our refractometer, in particular for the determination of the water vapor concentration in air are reviewed.!11
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机译：摘要：我们描述了一种用于空气折射率测量的新型紧凑型折光仪。它基于双平面法布里·珀罗（Fabry Perot）干涉仪，其厚度不同的腔由同一可调频率的激光二极管独立照射。第一个1毫米厚的腔可以清楚地识别第二个（100毫米）的透射峰；激光频率被伺服锁定到后者。该折光仪不需要在测量过程中抽空任何部件。空气的折射率绝对值及其波动是通过拍频技术结合光学频率基准实时获得的。测量提供的分辨率为10 $ + $ MIN @ 10 $ /，并且相对精度为10 $ + $ MIN @ 8 $ /。我们还描述了如何使用折光仪测量质量标准比较中用于进行浮力校正的空气密度的波动。我们对折光仪的其他可能应用，尤其是在确定空气中水蒸气浓度的方法中进行了综述。！11
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