Research On Technology Of Spatial Phase-shifting Interferometry

Phase-shifting interferometry(PSI) is a highly sensitive optical measurement technology, which has such advantages like non-contact, high accuracy, nondestructive, whole field measurement, etc. and is widely used in manufacturing and metrology fields. The current phase-shifting interferometry system commonly used temporal phase shift method. But temporal phase-shift interferometry need to collect at least three phase-shift interferograms in the time sequence, so it is sensitive to environmental disturbances, and can only be suitable for static measurements; However, spatial phase-shift interferometry is able to overcome these disadvantages which limit temporal phase shift interferometry. Spatial phase-shift interferometry can collect real-time interferograms, so it is suitable for phase dynamic measurement and is not sensitive to the environment vibration. This paper focuses on spatial phase shifting interferometry technique expand the following aspects of the research work:1. Basic principle and system structure of spatial phase-shifting interferometer was discussed, and a Dual-channel spatial phase shifting interferometry system based on two step phase shifting method was designed. The system use an improved Michelson structure to split the light, and two polarizing plates whose polarizing directions are different with 45 degree are acted as phase-shifter,so two phase shifting interferograms is captured simultaneously in a single CCD camera.2. A spatial calibration technique based on the circular carrier technique was used to eliminate the error in current image mismatch calibration technique. In this technique, the circle carrier is introduced by defocusing a spherical test mirror in the test beam, and the relationship between the phase error and calibration error was used to correct the error of spatial location calibration. This technique can overcome calibration errors caused by calculation and has no need of calibration model.3. The basic image process method used in phase shifting interferograms are studied and discussed. The discrete Hilbert transform are used as phase extraction algorithm, filter algorithm and phase unwrapped algorithm was analyzed and selected to acquire low noise,high quality image.4. A two-step phase-shifing interferometer was set up and the real measurement of glass surface was conducted using this system, in the end, the system error was analyzed. The experimental results verified feasibility and stability of this system and demonstrated that in the laboratory environment, the root mean square(RMS) of repetitive results is less than 0.02?, so the system can be used in the measurement of microsurface profile and has good stability. After analyzing the error sources, it was indicated that the error of phase-shifting and the error of carrier are main errors of this system.