Periodic Nonlinear Error Suppression And Measurement Of Heterodyne Laser Interferometer With Separated Beams

In recent years,with the rapid development of ultra-precision equipment manufacturing,precision measurement and advanced scientific research,the demand for displacement measurement accuracy has gradually changed from nanometer scale to subnanometer or even pimeter scale,which presents new challenges to heterodyne laser interferometry technology.Heterodyne laser interferometry with separated beams proposed in this field is called "the next generation heterodyne laser interferometry ",which is the most promising method to achieve the measurement accuracy.However,the periodic nonlinear error caused by the ghost reflection,whose amplitude ranges from tens of picometer to one nanometer,is one of the important errors that hinder the improvement of the accuracy of heterodyne laser interferometers with separated beams.This error can not be accurately analyzed,suppressed and tested,leading to the current heterodyne laser interferometer with separated beams is still troubled by this error,which restricts the realization of measuring accuracy of heterodyne laser interferometer with separated beams at the pimeter scale.This thesis focuses on the periodic nonlinear error in heterodyne laser interferometry with separated beams.A method for analyzing periodic nonlinear error of heterodyne laser interferometer with separated beams is established,and the corresponding suppression and measurement method of periodic nonlinear error are proposed in the thesis.The specific research contents are as follows:Aiming at the problem that precise analysis of periodic nonlinear error induced by complicated ghost beams in heterodyne laser interferometry with separated beams is difficult,a precise analysis method of periodic nonlinear error based on feature beam extraction is proposed.The phase difference induced by different ghost beam paths is analyzed,and vector analysis of the ideal interference signal and the parasitic interference components introduced by the ghost reflection is performed.A ghost beam tracing model included key parameters such as intensity,trajectory and direction of multi-order ghost beams in interferometer is established.Then,the different orders of ghost beams are separated and extracted and the parasitic interference signal formed by the interference with the main beam is obtained.Finally,the accurate calculation of the nonlinear error induced by ghost reflection is realized.Aiming at the problem that the periodic nonlinear error of heterodyne laser interferometry with separated beams is difficult to be suppressed to picometers level,a method for suppressing periodic nonlinear error of heterodyne laser interferometry with separated beams based on precise planning of ghost beam traces is proposed.This method bases on the precise analysis of periodic nonlinear error.By trajectory back analysis of multi-order Doppler frequency shift ghost beam,the key ghost reflection surface that generates these beams are obtained.Then,the mapping relationship between the spatial attitude of the key ghost reflection surface and the periodic nonlinear error is construct.The space attitude of the key ghost reflection surface are optimized to accurately plan the trajectory of the ghost beam.The parasitic interference signal induced by the ghost beams is reduced.Thereby,the periodic nonlinear error in heterodyne laser interferometry with separated beams is suppressed to picometer level.Aiming at the problem that the periodic nonlinear error of heterodyne laser interferometry with separated beams is difficult to be measured by existing method,a periodic nonlinear error measurement method based on double channel parasitic component synthesis is proposed.The dual-direction Doppler frequency shift characteristics of heterodyne laser interferometry with separated beams is analysed.The measurement/reference signal containing the parasitic Doppler shifts of each order is simultaneously subjected to double channel parasitic component synthesis with two pairs of the same local quadrature signals.After secondary mixing,a pair of quadrature signals with varying amplitudes are obtained.The form of the periodic nonlinear error in the heterodyne laser interferometer with separated beams is converted from the parasitic Doppler frequency shift of each order of the measurement/reference signal to the amplitude change of the quadrature signal to be measured.Thus,the periodic nonlinear error of the entire interferometer is realized.On the basis of the above research,a number of experimental devices are designed and built to verify the analysis,suppression and measurement methods of periodic nonlinear error in heterodyne laser interference with separated beams.First,the precise analysis method of periodic nonlinear error based on feature beam extraction proposed in this paper is experimentally verified: the periodic nonlinear error in the Wu-type interferometer with retroreflector and mirror are compared and tested.The experimental results are consistent with the simulation analysis results;the experiment testing the periodic nonlinear error induced by coupling of polarization leakage and ghost reflection is consistent with the simulation analysis results,which proves the correctness of the periodic nonlinear error precise analysis method proposed in this paper.Then,the periodic nonlinear error measurement method based on double channel parasitic component synthesis is verified,and the measurement error is better than 2 pm.Finally,the periodic nonlinear error of the Joo-type interferometer with retroreflector is suppressed based on the precise planning of the ghost beam trace and is then tested.The results show that,through the optimization design of this method,the periodic nonlinear error of the Jootype interferometer with retroreflector is suppressed from tens of picometers to below 5pm.