Research On Optical Testing By The Point Diffraction Interferometer

The development of the ultra precision instrument is very important in the futurescience and technology and the key to manufacture this kind of instrument is how tomanufacture the optic which is “good” enough. However, the accuracy of the traditionaloptical shop testing technology, such as Michelson inteferometry and Fizeauinterferometry, is limited by the reference wave which is produced by the reflection ofthe reference surface. The point diffraction interferometry (PDI) introduced in thisthesis not only has simple system configuration but also produces the reference wave bypinhole diffraction, so it can reach higher precision and accuracy. This thesis that isdevoted to basic research and the development of the key technology and problems ofthe point diffraction interferometry, is organized into five sections:（1） The domestic and overseas development status about the optical testingtechnology achieving high accuracy and precision is adequately investigated andthe history of the point diffraction is also reviewed. Based on the principle of thePDI, the experimental system, working process and the application protencial arediscussed. The involved key problems and technical difficulties are analyzed.（2） The deviation between the pinhole diffracted wave and the perfect sphericalwave is the keypoint of the accuracy of the PDI. The methods of calculating thepinhole diffracted wave are investigated and analyzed. A new way, based on FiniteElement Method (FEM) and Rayleigh-Sommerfeld scalar theory, is proposed toestimated the deviation and the influence of the system error on the diffracted waveis also numerical stimulated.（3） The system configuration of the PDI that be used to test spherical figure andthe phase shift interfermetry are discussed. The the interferogram processing isnumerical simulated. The main errors of the PDI and the theory accuracy that thePDI can reach are analyzed.（4） Calibration of the system errors is indispensable to estimate the accuracy of themeasurement devices. A new configuration, which is easier to make the alignment,of the null test method is proposed and set up. A method to align the focus spot ontothe pinhole with the help of two windows and a new way to calculate the relative position between the detector and the diffraction mask by processing theinformation on the intergram are proposed. The origin of the system errors and themethods to reduce those errors are analyzed. The relationship between the null testresult and the accuracy of the PDI is discussed.（5） A PDI experiment system is set up and a convace mirror which has thediameter of25mm and the radius of250mm is tested. The testing result is comparedwith another result tested by ZYGO interferometer. The main system errors areanalyzed.The PDI, which has got rid of the limitation of the reference surface, is prior toother measurement instruments in ultra precision figure testing. The research in thisthesis will be the theory and experiment foundation of the application of the PDI.