Research On The Technology For The High Precision Testing Of Three-dimensional Shape With Steps By Dual-wavelength Phase-shift Interferometry

The surface morphology of elements with steps are non-continuous and abrupt,which have two morphology characteristics parameters such as the macroscopic substrate and the microstructure.Especially for the infrared elements with steps,the departure of aspheric surface for the macroscopic substrate is higher,and the step height for the microstructure varies at the micron scales.Interferometry is the most widely used method for the the high precision testing of three-dimensional shape.However,the conventional single short-wavelength interferometer cannot test the macroscopic and microscopic morphology simultaneously,for the 2? phase ambiguity problem due to the uncertainty of fringe orders which is limited by the working wavelength.By obtaining the interferometric information of the long equivalent wavelength,dual-wavelength interferometry can determine the fringe orders and extend the measure range to several micrometers and even millimeter level.In this dissertation,research on the key technology for the dual-wavelength interferometric testing of the macroscopic and microscopic morphology for the elements with steps is carried out.And we will discuss the development of interferometer,the measure methods for elements with high reflectivity,and the phase retrieval method from moiré fringe patterns.To test the large-scale variance of the substrate deformation for the elements with steps,we have developed a dual-wavelength phase-shift Fizeau interferometer(DWPSI).The working wavelengths of DWPSI,which can overcome measuring limitation of the conventional single short-wavelength interferometer.The working wavelengths of DWPSI are 632.8 nm and 532 nm,and the corresponding long equivalent wavelength is 3.34 ?m,which extend the measure range of morphology to micrometers.In addition,for the measurement of the cuved elements with steps,we presented a transmission sphere configuration with small F-number which constitutes an approximate unfocused front group and the aplanatic lens.This configuration offers a loose distance tolerance between front group and the aplanatic lens,which is among the range of ±20 mm.Finally,the dual-wavelength transmission sphere is assembled by the Optical Center-Deflection-Measure Instrument,and its optical accuracy is better than ?/20 PV(?=632.8 nm).The developed DWPSI and dual-wavelength transmission sphere provide experimental foundation for the high precision testing of three-dimensional shape with steps.For the elements with steps made by silicon and germanium materials,the reflectivity is higher in visible wavelengths.And the phase retrieval errors will be introduced by the multi-beam interference.A single-wavelength ?/4 Carrier Squeezing Interferometry(QCSI)method was proposed to suppress the influence of the harmonic components and phase-shift error simultaneously.Simulation results indicated that the phase retrieve accuracy is better than 0.008?(PV,?=632.8 nm),even when the reflection coefficient of the test surface is as high as 0.9.Combining the QCSI method and the dual-wavelength asynchronous phase-shift interferometry technique,the dual-wavelength multibeam interferometric phases synthetization(DMPS)method is presented.By fusing the phases of equivalent wavelength and single wavelengths,the integer and decimal parts of synthesized phase could be obtained to retrieve phase in testing steps with high reflectivity.When the morphology for the steps with the aspheric and large devation substrate varies strongly,the single-wavelength interference fringes are too close to identify in the dual-wavelength asynchronous phase-shift interferometry.And for this,the low-frequency moiré fringe phase-shift interferometry method in dual-wavelength simultaneous phase-shift interferometry is presented.For the separation of the high-frequency single-wavelength fringe and the low-frequency moiré fringe,the distribution model for the moiré fringe intensity was established and the equivalent wavelength phase-shift interferometry(EPI)method was presented.Merging the additive-to-multiplicative moiré transition,the spatial carrier technique,and the spectrum filtering technology,EPI method could extract the equivalent-wavelength interference fringes and demodulated the phase from the moiré fringe by the conventional phase-shift algorithms.To reduce the impact of phase-shift error further,the Carrier Squeezing Dual-wavelength Interferometry(CSDI)approach was proposed based on the Carrier Squeezing Interferometry(CSI)technique.When the distribution range of the phase-shift error is as high as ± 10%relative to the 7r/2 phase shift step at the equivalent wavelength,the accuracy of phase retrieval is better than 20 nm PV.The restrictions of spatial carrier would affect the application of CSDI method.To reduce the difficulty and increase the robustness of the process for the moiré fringe,the equivalent wavelength temporal phase retrieval method was proposed.By adopting the ?/(2k)phase shift at the equivalent wavelength,the spectrum separation of the temporal moiré fringe intensity,and the conventional phae-shift algorithm for the equivalent wavelength phase-shift interferogram,the proposed method could abandon the limiting conditions of spatial carrier for moiré fr inge.And the high precision three-dimensional shape of the elements with steps could be obtained without the spatial carrier.