A method to improve the precision of interferometric phase-recognization under open-loop PZT drive

For the monochromatic light interferometry under open-loop PZT drive, a high precision method for phase recognization that satisfies the four steps phase-shift algorithm is proposed. The total idea of the phase recognization method is as follows. Firstly, two pixels with suitable phase-difference are selected from the interference field and the interference equations of the two pixels' gray values are established in one driven cycle of PZT. Secondly, the parameters of interference equations can be obtained by using ellipse fitting algorithm. Thirdly, the point-to-point step length of PZT drive and sequence phases can be determined through reverse calculation of sequence phases. Finally, in order to calculate initial phase of every pixels four interference grayscale images that meet the four steps phase-shift algorithm are designed and calculated through Lagrange parabolic interpolation. The experimental results have shown that this method decreases the requirement for hardware, environment and needs less interference grayscale images than traditional methods. The method can meet the high precision demands of surface topography measurement and has high processing speed.