Synthetic model of nonlinearity errors in laser heterodyne interferometry.

The development of laser heterodyne interferometry raises the requirements of measurement resolution and accuracy. However, periodic nonlinearity errors mainly suppress the accuracy of laser heterodyne interferometry. Based on the generation mechanism of nonlinearity errors, the sources of nonlinearity errors in laser heterodyne interferometry are first analyzed in this paper. Then, a synthetic model is established to analyze the influences of various nonlinearity error sources on the first- and second-harmonic nonlinearity errors. The first-harmonic nonlinearity errors can be reduced and suppressed by adjusting the orientation error of optical elements in a heterodyne interferometer. Furthermore, the azimuthal misalignment of the polarization beam splitter (PBS) is the main source of the second-harmonic nonlinearity errors. Therefore, when in heterodyne interferometer, the azimuthal misalignment of the PBS should be avoided if possible. This study provides theoretical basis for reducing and compensating nonlinearity errors in a laser heterodyne interferometer.