Improved measurement accuracy in heterodyne laser interferometer using WDF

The heterodyne laser interferometer is restricted by some unwanted nonlinear and environmental errors which are caused mainly from the frequency-mixing and the non-uniformal air refraction, respectively. Such errors act as an obstacle for measurement accuracy, especially in nanometer scale. Proposed is a compensation algorithm based on the WDF (weighted least square: WLS and data fusion: DF) method to improve measurement accuracy. The WLS method has a capability of minimal reduced error to eliminate the nonlinearity error in a laser interferometer. In the DF method, two laser heads used to obtain multiple measurement data are combined together to reduce environmental errors.