In-line Calibration of Phase Shifters for Interferometer Measurement

In phase-shifting metrology, the accuracy of phase measurement is directly affected by the phase-shifting error, Accurate calibration of phase-shifter is very important if good measurement results are expected. A new in-line high accuracy phase-shifting calibration method based on Damped-Least-Square algorithm which provides stable convergence and accurate phase distribution is presented. By intercepting a line on the same position from a series of interferograms associating with the phase-shifter's characters and constructing the mathematic model for intensity of the line on each interferogram, the correlative coefficients of the mode's function can be solved, one of which is the wrapped phase. Then the voltage-unwrapped phase curve is obtained through unwrapping technique. Results of computer simulation show a high accuracy after several fast iterations. In addition, taking an experiment for example in our interferometer, the characteristic curve of phase shift over voltage change is presented in the end. Experiment results show it can be an in-line calibration method for phase-shifer in PSI.