| Heterodyne interferometer is a measuring instrument which was developed from early seventies of twentieth century. Heterodyne interferometer plays an important role in the technology field of precision measurement because of high accuracy by means of its simple phase comparison method, simple structure, strong anti-interference ability and convenient operation. With rapid development of microelectronics, microelectromechanical systems and ultraprecision machining in 21 th century, how to improve the measuring precision to submicron and nano meter-scale needs to be solved urgently. Heterodyne interferometer has unique advantages on nano meter-scale measurement. However, due to its inherent nonlinearity error, heterodyne interferometer is difficult to implement meansurement in nano meter-scale. Therefore, research on the phase compensation method and technology for nonlinearity error in heterodyne interferometer becomes an important subject nowadays.In this dissertation, by means of the study on the frequency mixing phenomenon which is generated by the elliptically polarized incident light in the optical arms of heterodyne interferometer and the principle of phase comparison, two basic measuring relationships in interferometer and the definitions of linear phase shift, non-linear phase shift and nonlinearity in interferometer are proposed explicitly. All possible optical reasons which have influences on the non-linear phase shift are studied by theoretical analysis and quantitative test. Based on the model of non-linear phase shift and basic measuring relationships in heterodyne interferometer, a phase compensation method to eliminate nonlinearity is proposed. This method is proved theoretically and is described properly in the dissertation. Then the performance of compensation system for nonlinear phase shift and the key technology to implement this method are both studied. Experiments show that this method can eliminate the first order or high order nonlinearity error in heterodyne interferometer effectively. This simple measuring method can easily eliminate nonlinearity error from inside. The main works and achievements of the dissertation are listed in the following.1.Starting from two equations of elliptically polarized incident light, the basic principle of heterodyne interferometer is introduced in the dissertation. The frequency mixing phenomenon which is generated by the elliptically polarized incident light in the optical arms of heterodyne interferometer, which leads to the nonlinear phase shift, is studied and the definitions of linear phase shift, non-linear phase shift and nonlinearity in interferometer are proposed properly. Two basic measuring relationships in interferometer are given by means of the study of the characteristics of nonlinearity and the principle of phase compensation.2. All possible optical reasons which have influences on the non-linear phase shift are studied by theoretical analysis and quantitative test. The effects on nonlinearity which are generated by the error in the wave plate are emphatically analyzed and four conclusions are given. “Double Phase Measurement” is utilized to test different nonlinearity phase shift in heterodyne interferometer. The quantitative boundary of the nonlinearity in heterodyne interferometer is obtained. The nonlinearity error reaches from ten nanometers to twenty nanometers or so.3. Based on the model of non-linear phase shift and the basic measuring relationships in heterodyne interferometer, a phase compensation method to eliminate nonlinearity is proposed, proved theoretically and described properly in the dissertation. The essence of this method lies in controlling the polarizer which is mounted in front of the photoelectric receiver in interferometer to rotate to the setting angle according to the phase difference signal. Therefore the nonlinearity phase shift is compensated and the nonlinearity error in interferometer is eliminated. By means of studying the characteristics of dichroic polarizer, the compensation method on the nonlinearity phase shift is analyzed and the model of the nonlinearity phase shift with the function of nonlinearity compensation is given. The relationship between the rotation angles of polarizer and the nonlinearity phase shift is proposed.4. By means of the analysis of structure of optical path, the distribution of phase error in the ideal state and the actual state is given with the change of measuring environment and measuring process. The relationship between system input and output and the relationship between angular velocity of polarizer’s rotation and beat frequency are proposed based on the study of measuring system. After analyzing the characteristics of main optical devices in the system, the type of laser source, ordinary spectroscope, polarizing spectroscope, cube-corner prism, 1/4 wave plate and polarizer are given in the dissertation.5.According to the basic principle of the nonlinear phase compensation method, hardware of then testing system and flow chart of the control system program are designed in the dissertation. PWM current loop servo amplifier and PID controller are designed. The model of servo system for polarizer controlling is established and its basic characteristics is also studied.6. Experimental researches are carried out to prove the nonlinear phase compensation method. An experiment platform is designed and experiments with or without phase compensation are implemented. Experiment data and the processing method are shown. Finally, experiment results are analyzed and a conclusion is drawn in the dissertation. |
PDF Full Text Request