Research On Full Field Heterodyne Fizeau Interferometer Technology

Optical interference detection technology has the advantages of high precision and noncontact measurement.It plays an irreplaceable role in many major scientific and technological fields.With the development of scientific technology,the phase-shift interferometer designed by the combination of various technologies has greatly improved the detection accuracy of the instrument.With the advantages of reference light and measurement light co-optical path,the Fizeau-type interferometer has a strong anti-interference ability,which attracts the attention of optical detection personnel.At present,most commercial interferometers on the market use the Fizeau-type structure.The phase shift mode of this instrument adopts piezoelectric ceramic(PZT)mechanical and polarization phase shift.However,these two phase-shift methods have their own application limitations.In this paper,a full field heterodyne Fizeau interferometer based on the acousto-optic effect to achieve heterodyne phase-shift is proposed.The developed principle prototype can achieve high-precision detection of planar optical elements.First of all,in order to achieve low-frequency heterodyne interference,the Mach-Zehnder interference optical path is adopted.The low-frequency difference of +2.5Hz and-2.5Hz is generated by using the acousto-optical frequency shifter on the two beam splitter paths.Two beams with stable 5Hz difference frequency are obtained as heterodyne light sources.A large number of interferograms with periodic changes are collected by using a high-speed detector which sampling frame frequency is greater than the difference frequency of heterodyne light source.Combined with Fourier transform phase extraction algorithm to solve the measured surface profile.The heterodyne interference theory and the Fourier transform phase extraction algorithm are derived.The Fourier transform and the four-step phase-shift phase extraction algorithm are compared and simulated.Then,the prototype of full field heterodyne Fizeau interferometer is investigate and a simplified experimental device is set up to verify the feasibility of the principle optical path of full field heterodyne Fizeau interferometer.The relationship between the heterodyne double beam spacing and the off-axis amount of the double beam and the wavefront quality of the two beams after collimation and the relationship between the size of the filter aperture and the imaging quality of the interferogram are analyzed.The off-axis collimator optical system and imaging lens optical system of the internal light source of the interference cavity are designed.The design of the mechanical structure of the full field heterodyne Fizeau interferometer is completed,including the heterodyne light source module,the Fizeau interference cavity module related optical element fixed support,the electronic component fixed support,the standard flat crystal adjusting frame and so on.Finally,experiments are carried out on the repeated measurement accuracy and cavity accuracy detection of full-field heterodyne Fizeau interferometer principle prototype.The Fourier transform phase extraction error is analyzed,which caused by the non-ideality of the frequency shift of the acousto-optic frequency shifter due to environmental factors.The energy center of gravity method is used to optimize the Fourier transform phase extraction algorithm and improve the detection accuracy of the full field heterodyne Fizeau interferometer.