Research On Dynamic Fizeau Interferometer Based On Lateral Displacements Of The Point Sources

Dynamic interferometry is used to solve the problems that time-domain interferometry can't work effectively in an unsteady environment.Multiple phase-shifted interferograms can be captured at the same time with this technique,so as to realize the real time measurement of unstationary objects.It can be widely used in aerospace,astronomical optics,biomedicine and other fields.Especially in the unstable measurement occasions with time-varying factors such as vibration,turbulence and temperature drift,its advantages are more prominent.Most of the existing dynamic interferometry methods are based on polarization phase-shifting technique.When using this method for the measurement,the residual stress of optical materials will introduce additional phase shift,which results in phase shift error.Therefore,the polarization phase-shifting dynamic interferometry is difficult to be applied to the detection of large aperture optical elements.In order to solve the above problem,the non-polarization dynamic interferometry based on lateral displacements of the point sources is proposed,which is applied to Fizeau interferometer,and the dynamic Fizeau interferometer is proposed.In this paper,a dynamic Fizeau interferometry based on lateral displacements of the point sources is proposed.The mathematical model of phase shifting for lateral displacement of point source is established and the principle formula is derived.The light source of the interferometer is designed as a point sources array,and phase shifts can be introduced in the interferograms simultaneously due to the different lateral off-axis displacements of the sub-light source.Four interferograms are captured separately and clearly,under the assistance of a specially designed imaging lens array.Four phase-shifted interferograms are captured instantaneously with the imaging lens array and the dynamic measurement is realized.The two key techniques of simultaneous phase-shifting and beam duplication are researched.The point sources array is generated with the specially designed chessboard phase grating,the phase step of ?/2 is achieved by adjusting the displacement of the point sources array to the optical axis.For the four quadrants molded lens module,the separation and conjugate relation model for interferograms is developed,and then the lens module is developed.By embedding the module in the bi-telecentric imaging system,the spatial separation and conjugate imaging of the four phase-shifting interferograms are achieved.The dynamic Fizeau interferometer with the aperture of 100 mm based on the lateral displacements of the point sources is designed and built.The short focal length of collimating lens limits the size of point light source array in the system.In order to solve the contradiction between the smaller size of point light source array and the larger size of lens array,the collimating optical path is separated from the imaging optical path to enlarge the aperture of the sub-lens in the imaging lens array to realize the high resolution of the imaging system.Instead of using long focal length collimating lens,the system is miniaturized.The system is built and applied to the measurement of plane mirror,spherical mirror and dynamic liquid surface.The dynamic Fizeau interferometer with the aperture of 600 mm based on the lateral displacements of the point sources is designed and built.Because the focal length of the collimating lens is long enough and the size of the point sources array is large enough,the large-size imaging lens array can be obtained without separating the collimation and imaging functions of the collimating lens,and the high resolution of the imaging system can be realized.According to the above design scheme,the interferometer is built.The influence of air flow,temperature gradient and constant temperature on the measurement results is analyzed,and the environmental control methods are studied.The interferometer is applied to the measurement of plane mirror and transmission window.The systematic error in the proposed dynamic Fizeau interferometer is discussed and analyzed.The error sources and control methods of the system are studied.The systematic errors of interferometers with different apertures are analyzed and compared.It is found that the 600 mm interferometer has stronger tolerance for systematic errors.The position mismatch error of the interferograms is analyzed and discussed.A fast position matching algorithm based on partial phase correlation is proposed to realize the spatial position matching of the interferograms.