General Interferometric Aspheric Testing With Partial Null Lens

The application of aspheric optics is currently growing in all types of optical systems.Nowadays,optical elements with surface fabrication accuracy of 10nm can be achieved,but general aspheric testing with relatively high precision keeps to be a challenging task.For its high precision,high sensitivity and great repeatability,interferometry serves as a common way for surface figure error precision measurement.To improve the flexibility of testing various aspheres,interferometry employing different non-null system configurations are being studied by several teams from America,the UK,Germany and China,etc.Major research of this dissertation is on general interferometric aspheric testing with partial null lens(PNL),containing theoretical design,algorithm analyses,elements control and experiment demonstration based on the prototype.The content includes:A series of PNLs is established.After analyzing the advantages of testing aspheres with aspherical wavefront,PNL design based on bidirectional constraint is realized.By proposing a method for solving compensation range of a single PNL,a series of PNLs is designed,optimized and established with less member to cover more testable range.Corresponding database is built which helps match the optimum PNL for a certain test part.These researches provide theoretical basis for general aspheric testing with PNLs.Algorithms of retrace error correction are studied.The concept of inherent and unpredictable retrace error is proposed after the introduction of retrace error correction methods.From this viewpoint,principle and correction ability of three commonly employed algorithms are analyzed.With the proposed double ray tracing method and the method for middle and high frequency figure recovery,the uniform expression of the reconstructed figure error after retrace error correction is achieved.By the study of retrace error correction ability and posture and position tolerance of the test part for the three algorithms,choice of an appropriate method and the aspheric posture and position control demand are supposed.General data processing for aspheric testing is achieved and the program for testing procedure control is designed.By realizing the simulation of real interferometric system for aspheric testing without commercial optical design software,retrace error correction of the detected wavefront is also feasible on the same platform.In addition,the trust region algorithm is recommended to solve the nonlinear optimization problem.With the self-directed data processing and testing procedure control program based on a same platform,aspheric testing relying on multi-platforms,multi-softwares,complex operations,high cost and program redundancy are avoided,providing software guarantee for the general aspheric testing.Methods for posture and position error control of the key elements are proposed.After analyzing the wavefront aberration due to the errors of PNL and asphere,existed error control methods and their corresponding accuracy are introduced.By proposing the posture control method based on double imaging,and position determination method with database matching or optimization searching,the efficiency and universality of the element adjustment method are improved,simplifying the system structure at the same time,which guarantees the final testing accuracy.Experiments are executed for the validation of the general interferometric aspheric testing with PNL.A series of PNLs are designed and fabricated.With these.PNLs,experiments of the posture and position control of the key elements,aspheric measurements and influence to the reconstructed results due to retrace error correction methods under different testing conditions are carried out.The experiments verify that general aspheric testing is feasible based on PNL,whose testing results match well with those of the null test.With appropriate retrace error correction method,the system dynamic range can be enlarged and relatively high accuracy is achieved.