Study On Ultra-high Accuracy Phase Shifting Point Diffraction Interferometry

Ultra precision optical element surface figure and system wavefront test play an important role in important engineering projects and cutting-edge scientific research,such as projection lithography,gravitational wave detection and inertial confinement laser nuclear fusion.In order to break through the technical blockade of foreign countries,technical research in this field is needed.The phase shifting point diffraction interferometer(PSPDI)technology,which takes the nearly ideal spherical wave generated by pinhole(submicron)diffraction as the reference,eliminates the influence of the reference surface error of the traditional interferometer,and can realize very highprecision wavefront measurement(0.1 nm RMS).In this paper,the key problems of PSPDI,such as ultra-high precision optical wavefront reference generation,ultra-high precision phase-shift interference data processing,system error suppression,accuracy evaluation,are studied.The PSPDI is applied to precision optical measurment.The details are followed as:First,ultra-high precision optical wavefront reference generation.The pihole fabrication and alignment are key technologies of optical wavefront reference generation.It is difficult to achieve precision alignment better than 100 nm on submicron pinholes.To solve this problem,a fast and precision pinhole alignment method and device are proposed,which can achieve precision alignment better than 30 nm in half an hour.Second,phase-shifting interference information processing.The anti-error phase extraction algorithm based on weighted least square method is designed.The wavefront propagation method is studied.Third,systematic error analysis and suppression.The error source of PSPDI is analyzed.The random error is verified by simulation,and the performance requirements of key components and environmental control requirements are presented.Aim at the presented error sources,the error suppression method and absolute measurement method are given.Fourth,The PSPDI is developed and experimental evaluation is perfomed.The measurement stability and measurement accuracy of the self-developed PSPDI are evaluated.The experimental results show that the measurement stability of the selfdeveloped PSPDI reaches 0.05 nm RMS;The systematic error of the self-developed PSPDI is evaluated by rotation and translation absolute test method.The evaluation results show that the systematic error of the PSPDI is 0.18 nm RMS.The measurement accuracy better than 0.1 nm RMS can be achieved by deducting the systematic error from the measurement results.Fifth,the application of PSPDI.The self-developed PSPDI is applied to the spherical wavefront calibration accuracy evaluation of aspheric testing device,system wavefront test and ICF microsphere surface defect detection.In the former application,the direct measurement results of PSPDI are cross compared with the absolute test of Zygo MST to evaluate the effectiveness of the absolute test method of Zygo interferometer.The wavefront test and integrated assembly and adjustment platform of EUVL projection optics based on PSPDI is established,and the precise test and assembly and adjustment of small field projection optics is achieved.In the ICF microsphere surface defect detection,the overall scheme design,technical route design and index response analysis are completed according to the index requirements.The key indexes such as transverse resolution,longitudinal resolution,measurement repeatability,measurement range,measurement efficiency,microsphere position adjustment accuracy,rotation accuracy and sub aperture stitching are analyzed and simulated respectively.The detailed design of the subsystem,the selection of key components,the design of integrated assembly and adjustment scheme and the research of data processing method are completed,and the full coverage measurement process and measurement strategy are established.Finally,an experimental system is established to measure the defects with 4 ?m transverse size.