Research Of Nonlinearity Measurment Technology In Laser Heterodyne Interferometry Based On Lock-in Amplifier

As the development of the ultra-precise area,such as the detection of gravitational waves,heterodyne interferometer attracts thousands of researchers' attention.And its measurement accuracy has been developing continuously.Periodic nonlinearity error is one of the measurement errors of heterodyne laser interferometer,which severely limits its measurement accuracy.The coaxial heterodyne laser interferometer which is developed at first is caused by the frequency aliasing.the nonlinearity of this coaxial heterodyne laser interferometer is of up to several nanometers.Then the non-coaxial heterodyne laser interferometer is developed.The nonlinearity of the non-coaxial heterodyne interferometer is caused by ghost reflection and is reduced to the picometer.Non-linearity error testing is becoming more and more concerned as a basis for nonlinear compensation and suppression.On the one hand,the nonlinear test results are one of the important indexes to measure the performance of heterodyne laser interferometer.On the other hand,the size of the nonlinear component plays an auxiliary role in the optimization of the heterodyne laser interferometer.At present,the common heterodyne laser interferometer nonlinear test methods include lock-in amplification method,spectrum method and scanning method.In this paper,the traditional locking phase non-linear test method has a narrow working bandwidth and cannot do the harmonic analysis for the non-uniform motion,and the test result has a drift.A nonlinear measuring system based on double lock phase amplification is developed.The main research contents are as follows:Firstly,the dynamic performance of the traditional lock-in amplifier nonlinear test method is analyzed,including the working bandwidth and the test condition of different types of interference system,and the influence of the intensity change alignment test result.Aiming at the problems existing in the traditional lock-in amplification method,a nonlinearity measuring system based on double-lock phase amplification is proposed,which can be applied to more interference systems.A nonlinear and displacement synchronous testing technique is proposed to make it different.The influence of light intensity fluctuation on the nonlinear test results is avoided.Based on the principle of double lock phase amplification,nonlinearity and displacement synchronization test and adaptive algorithm,a nonlinearity measuring system based on double lock phase amplification is designed.There is a signal processing module after transferring the optical signal to the electric signal.It is used to amplify and filter the measuring and reference signal.The double-lock phase amplification module utilizes the internally generated reference signal to mix the two output signals separately.The non-linear and displacement signal processing platform uses the adaptive nonlinear test algorithm.At last the relation between the nonlinearity and displacement of the Interference System is got by the platform.Finally,through the analysis of the performance of the nonlinear test system proposed by this experiment,the comparison between the traditional lock-in amplification method and the improved lock-in amplification method,including the test system test error and the interference non-linear test results of the system.The non-linearity of the lock-in method,the spectrum method and the scanning method are compared with the same interference system.The test results of the three methods are basically the same.