Heterodyne displacement measuring interferometry has been widely used to calibrate other measurement devices such as capacitive sensors, inductive sensors, and optical encoders because of its high dynamic range, high signal-to-noise ratio, and direct traceability to the length standards. The three main error sources that limit the performance of a displacement interferometry system are the laser frequency stability [1], refractive index fluctuations in non-common optical paths [2], and periodic nonlinearity in the measured phase due to source mixing, manufacturing tolerances, and imperfect alignment [3, 4, 5]. While the effects of the laser frequency stability and refractive index fluctuations can be mitigated by employing a highly stable reference laser and by performing the measurements in a well controlled environment or even vacuum, the periodic nonlinearity is difficult to eliminate.
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