Research On Φ100mm Wavelength-tuned Phase Shifting Interferometry With High Repeatability

The requirement for high precision optical devices promotes the development ofoptical test and the level of optical test could determine the precision for fabrication inreturn. Phase shifting interferometer (PSI) is the most popular method in highprecision testing of optical surfaces, among which the mechanical phase-shiftinginterferometer utilizing piezoelectric transducer(PZT) as the phase shifter is the mostwell developed. However, the mechanical phase-shifting interferometer will bring insome nonlinear errors which limit the precision when detecting optical devices withlarge diameter. Wavelength-tuned phase shifting interferometer (WPSI) canimplement phase shifting through altering the wavelength outputted by tunablesemiconductor laser, we need not have to change the position of the relevantcomponents in the interferometer during the process, thus the nonlinear errors couldbe avoided and we can detect the large-diameter optical devices with higher precision.This paper aims at designing a Fizeau WPSI whose optical diameter is100mmand the surface RMS repeatability is better than λ/10000. Our work could begeneralized as follows: Firstly, the development status of phase-shifting and thefundamental principles for phase-shifting measurement was concluded, and thecommon phase-shifters’ working mechanisms as well as their defects and merits wereintroduced; Then, we researched on the universal expressional formulas for traditional phase-shifting algorithm by Fourier transform theory and analyzed the decline abilitytowards nonlinear errors caused by phase-shifter and detectors comparing four typicalphase-shifting algorithms, and based on the results we proposed some principles forchoosing the phase-shifting algorithms when designing the interferometer. Besides,this paper briefly introduces the layout for Fizeau wavelength-tuned phase shiftinginterferometer with the principles for phase-shifting measurement; Since thevibrations, turbulence of air temperature, instability of the laser light source and therandom errors caused by the noise in CCD camera could influence the RMSrepeatability when measuring the surface shape, this paper simulates and analysisesthe influence by direct algorithm and Monte-Carlo algorithm, and based on the resultswe achieve the choose for laser light and CCD for the experiment. Furthermore, themethod to calibrate the phase-shifting step for the phase-shifting interferometer wasresearched. This paper analysises the difference in step calibrating between PZTphase-shifting and wavelength phase-shifting; Also this paper compares the principlesand characters for Fourier Transform method and Advanced iterative least squarealgorithm(AIA) when calibrating the phase-shifting step; We proposed a novelphase-shifting algorith---two-frame differential average phase-shifting algorithm，TDA）to calibrate the phase-shifting step for the interferometer we designed based onthe needs of our experiment. Finally, this paper introduces the experimental device forthe Fizeau wavelength-tuned phase shifting interferometer we designed.And itssurface RMS repeatability and system error were measured respectively on the base ofcalibration for phase-shifting step implemented by the two-frame differential averagephase-shifting algorithm. The result shows that：the surface RMS repeatabilitymeasured by TDA is superior to0.07nm(1.106λ/10000) and could satisfy ourdesign requirement; we compare the measurement results for the same componentsutilizing our interferometer and Zygo interferometer respectively, RMS’ difference is0.742nm which indicates that our interferometer has a high precision.