Research On Adaptively Variable Null Interferometry For Complex Optical Surfaces

Complex surfaces represented by high-order aspherical surfaces and free-form surfaces will be the protagonists in the future optical system.Deterministic machining technology is an important technology for high-precision forming of complex optical surfaces.Deterministic machining requires to know the deviation of the actual shape of the in-process surface from the theoretical design shape,that is,the surface figure error.Therefore,it can be said that high-accuracy surface figure testing is the basic premise of complex optical surface ultra-precision machining.However,the contradiction between traditional interferometric null test technology and modern optical system requirements for optical component manufacturing is becoming more and more acute: The first contradiction is between the low-cost,high-volume manufacturing demand of modern optical systems for complex surfaces and the 'one-on-one' custom-made null test mode;the second is between the high-efficiency,high-precision manufacturing demand of modern optical systems for complex surfaces and the local large error of in-processing surfaces is the beyond the ability of interferometric test capability.In order to solve the above contradictions,the development of adaptively variable null test technology which can adapt a broad range of complex surface and can realize intelligent null has been widely concerned by researchers.The adaptively variable null test is expected to become the most potential technology to solve complex optical surfaces test problems.Variable null means to give interferometer the ability to generate variable aberration.Adaptve null means to give interferomter the ability to itellgently generate variable wavefront according to the unknown large surface figure error.However,in the development of adaptive variable null tet technology aiming at flexibility and intelligence,many basic scientific issues and key technical issues have not yet been resolved.The issues or techniques include the principle and law of variable compensation null,the phase control mechanism of adaptive null components,and the intelligently variable null mechanism of local severe error etc.Therefore,the fundamental research of adaptively variable null test including the related basic theories and key technical issues will innovate complex optical surfaces ultra-precision test methods,improve the flexibility and intelligence level of complex optical surface test technique.The improvement of test level has important scientific significance and engineering value.This thesis focuses on the flexible null and intelligent null requirements of complex surfaces test.Utilizing variable null technology and adaptive optics technology,a new adaptively variable null test method with flexibility and intelligence is developed.The theory,process and test system for complex optical surfaces adaptively variable null test are founded.The specific research content includes the following aspects:(1)For troubleshooting the limited flexibility issue of interferometric test for aspheric surface,a null test method based on variable spherical aberration null for aspheric surfaces is proposed.The principle and law of variable spherical aberration null test are revealed based on third-order aberration theory.The optimization design method and test ability evaluation method of variable spherical aberration null test are expounded.The test system based on variable spherical aberration null was researched and built.The evaluation of system measurement accuracy was carried out.The experimental verification of system test capability and test accuracy was carried out.The test system can adapt concave aspheric surfaces with departure ranging from 0 to 230?(?=632.8nm).The test accuracy is better than ?/40 root-mean-square(RMS).(2)To address the issue of poor flexibility of interferometric tests for free-form surfaces,a flexible test method based on spatial light modulator(SLM)for moderate freeform surfaces is proposed.The SLM encoding scheme based on interferometric type computer-generated hologram(CGH)is studied.The flexible null test system using SLM as programmable CGHs for freeform surfaces is designed.A freeform surfaces null test system based on SLM is built.The experiments show the test system can test moderate free-form surfaces with departure between 0 and 40?.The test accuracy is about ?/30 RMS.(3)Variable spherical aberration null test method can only generate a single aberration mode,and only aspheric surfaces can be tested.SLM method can only generate aberration with small amplitude,and only the moderate free-form surfaces can be tested.To troubleshoot these issues,a flexible null test method for free-form surfaces with large departure based on a hybrid refractive and diffractive variable null is studied.The theoretical model of the hybrid refractive and diffractive variable null is established,and the aberration compensation ability of the variable null is quantitatively evaluated.The optical path design of the free-form surfaces flexible test based on the variable null is described,and the measurement accuracy of the test system is evaluated.A flexible surface test system for freeform surface based on the hybrid refractive and diffractive variable null is established.The experiments show the test system can test moderate free-form surfaces with departure between 0 and 270?.The test accuracy is about ?/30 RMS.(4)To troubleshoot the issue of testing local large error of in-processing surfaces,the wavefron sensor-less adaptive optics(AO)technology is introduced into the field of interferometric test.Based on the anayze of traits of local large error and AO,the concept of adaptive wavefront interferometer is put forward.The theoretical framework of adaptive wavefront interferometer is established.The adaptive null algorithm is developed.The simulation verification of the using the adaptive wavefront interferometer to intelligently reason and variablely null local severe error is conducted.An adaptive wavefront interferometer test system is built.The theoretical analysis,simulations,and experiments show the test system can realize intelligent infer and null test of local large error with amplitude about 40?.The test accuracy is about ?/30 RMS.(5)The stochastic parallel gradient descent(SPGD)control method of adaptive wavefront interferometer shows poor adaptivity and high failure rate for different local large surface figure error.To troubleshoot this issue,the enhancement of adaptivity,robustness,and intellegence of adaptive wavefront interferometer is studied.In the framework of global optimization,the principle of adaptive wavefront interferometer is deeply studied.The low intellgence of adaptive wavefront interferometer is summerized to three optimization issues,namely objective function evaluation issue,non-convergence issue and local optimal issue.The introduction of machine vision gives the interferometer the ability to automatically analyze the fringes.Genetic algorithm is introduced to control adaptive wavefront interferometer.An adaptive wavefront interferometer test system controlled by machine vision and genetic algorithm is built and the experimental verification is conducted.The research results show the failure rate for different local large surface figure error decreases from 21% to 6‰.