Study On The Key Technologies Of In-situ Stitching Interferometric Test For Large Optics

Large plano optics are widely employed in space telescopes,laser fusion systems and other aspects.The demands of large size and high accuracy bring more and more challenges to the manufactory and measurement of that optics.The existed measurement methods are mainly offline testing techniques,which unable to meet the needs of high efficiency machining.Therefore,it needs to research efficient and precision measurement method to provide the basis of process analysis and quality assurance for ultra-precision large optical glass surface grinding machine.In view of the inadequacy of the existed measurement method for large size optical components,an in-situ testing method based on subapeture stitching interferometry is proposed according to the manufactory requirement of the ultra-precision large optical glass surface grinding machine.The corresponding in-situ stitching interferometric test system is developed,which provides a feasible and effective method for the in-situ measurement of large size plano optics.We have paid more attention to the research of relative fields,and the main results have been summarized as follows:1.Design of the in-situ stitching interferometric test systemAn in-situ stitching interferometric test system is developed to test large plano optics,which has an original framework integrated with the grinding machine and utilizes the one-dimensional movement of its piece carriage.The subaperture stitching technology is applied to extend the measured range and improve the lateral resolution.The dynamic interferometer is employed to scanning subapertures,which can effectively restrain the random error introduced by the environmental disturbance in workshop.The main technical parameters,such as the straightness and positional accuracy of the guideway,are put forward.The composition of the system is described detailedly.Subaperture stitching measurement software is developed synchronously,and the complete measuring process using this software for the in-situ testing is described.2.The in-situ interferometric stitching algrithem for large size plano opticsIn view of the high accuracy and high cost performance requirements of the in-situ measurement for large size optics,the subaperutre stitching technology is applied in the proposed system.The stitching algorithm by error averaging is expounded,including its mathematical model and calculation accuracy.The research focuses on analysis the cumulative effect of the second order error(defocus and astigmatism)in reference wavefront during the stitching process.The root cause of this kind of error accumulation is revealed.The cumulative formulas of defocus and astigmatism is derived when rectangle surface stitched by circle subapertures.The corresponding one-time compensation method is proposed which is no need to deal with each subaperture alone.The effectiveness of the proposed cumulative formulas and compensation method are verified by simulation and experiment analysis.3.Non-overlap subaperture interferometric testing methodThe in-situ measurement is used to control the shape of manufacturing surface,thus realizing very high testing precision is not economical.At the same time,in order to reduce the error introduced by the uncertainty of the test environment,a non-overlap subaperture interferometric testing method is proposed.This algorithm can efficiently reconstruct the low order surface shape of large size rectangle plano optics without overlap area between subapertures.Therefore,it can reduce the amount of subapertures.Although this method has its limitations,it is an effective method to improve the measurement efficiency of in-situ testing during grinding process.4.The analysis of error components and suppression methods of the in-situmeasurementFor the workshop environment of the in-situ testing,the main error components of subaperure interferometic stitching measurement are analyzed,which divided into two categories: measurement system error and random error.The retrace error is existed in the measured result when using this dynamic interferometer,and its influence on measurement accuracy is analyzed.The main parameters setting in dynamic interferometer are analyzed,which provided the actual operating basis in in-situ testing system.The error factors,which affect the measurement precision of single subaperture,are analyzed,including temperature,humidity,dust,vibration,alignment error and so on.The requirements of testing environment are put forward for the in-situ testing system.5.The verification of the in-situ testing systemMultiple repeatability tests of samples with different shape,size and texture are carried out using the in-situ testing system.The results illustrated that the developed system successfully realizes in-situ testing for large plano optics in the workshop environment.The system is reasonable and reliable.The stitching algorithm and error compensation method are effective.It can be used as the in-situ test method for processed workpiece by the ultra-precision grinding machine.