Novel Signal Processing Method in Heterodyne Interferometer for Improving the Accuracy

摘要

Data processing methods of common-path laser heterodyne interferometer (CLHI) is fully studied. To improve the accuracy of CLHI, three major sources of nonlinear-error, which include mis-orientation of incidence beam relative to Wollaston prism, elliptical polarization of laser beam and mis-orientation of two linear orthogonal polarization beams relative to metal-coated mirror, are theoretically investigated. The results show that the error from the Wollaston prism is mainly second harmonic and the error from the elliptical polarization of laser is first harmonic. We discovered that the mis-orientation of the metal mirror can also generate nonlinear errors, which had rarely been studied before. When the polarization directions of the two linear orthogonal incidence beams are not parallel (or vertical) to the normal plane of metal mirror, the reflecting beam will become elliptic polarized beam with orientation of the two ellipses having non-orthogonal and non-equal eccentricity. The frequency mixing may occur when the beam reflecting from the mirror passes through Wollaston Prism. The error caused by the frequency mixing is mainly first harmonic. Additionally the error compensation methods are also discussed to improve the accuracy of the interferometer.