DRIFT OF NONLINEARITY IN THE HETERODYNE INTERFEROMETER

A more comprehensive theory for the nonlinearity of heterodyne interferometer is given in this article. Our theoretical and experimental investigations of the nonlinearity drift indicates that the stability of the heterodyne interferometers is influenced not only by the thermal drift and long-term stability of the optomechanical parts, but also by the drift of inherent systematic nonlinearity; this drift is of particular importance in interferometer systems that have very small thermal drift. By means of a special detection method, the measurement drift caused by nonlinearity can be separated from the thermal drift and compensated for. Furthermore, a more complete method is devised for heterodyne interferometers to achieve high accuracy and stability.