The Key Technology Of Laser Differential Confocal Large Radius Measurement With High Accuracy

In the field of modern optical measurement, the radius of curvature (ROC) is one ofthe most fundamental parameters in optical lens. Its precision directly affects the otheroptical parameters, such as focal length, aberration and so on, which significantly affect theoverall performance of optical system. Up to now, the accurate measurement of ROC is stilldifficult in the modern optical measurement field, a difficulty of the modern opticalmeasurement. The request for the precision of ROC measurement is especially strict in thehigh-performance optical system such as space camera and the objective of the lithography.In order to solve the ROC accurate measurement problem, we once proposed the laserdifferential confocal radius measurement method. Based on the property that the zerocrossing point of a differential confocal intensity curve corresponds to the focus of theobjective，the system uses the zero-crossing point to precisely identify the cat-eye andconfocal positions of the tested device，and uses an interferometer to measure the distancebetween the two positions and achieve high-precision measurement of radius of curvature.Compared with other measurement methods, the laser confocal measurement method hasthe advantages of simple structure, high focusing sensitivity and anti-environment ability.To satisfy the large radius measurement, we carry out a series work，include the design ofkey components, the establishment of the beam path, the simulation of measurementprocess are all based on this differential confocal measurement of radius of curvature. Andthe main research work in this thesis includes:1) The analysis of radius of curvature measurement principle: based on differentialconfocal tomography characteristics and the ability of precise capture capability of theobjective focus point, the measurement principle of the differential confocal radius isresearched, the measurement method of the differential confocal radius is designed, and theresult effect of radius of curvature measurement causing by aberrations and offset isanalyzed.2) The research of the differential confocal radius measurement optical system: asimulation model is established in ZEMAX, and the parameters of each element and thesystem dimension are determined, the design of a4.5m focal length of collimating lens,which is a key component, was completed, and the effect of optical measurement resultscausing by spectral prism in the converging is analyzed. 3) The design of the differential confocal radius measurement system’s mechanicalstructure: mechanical structure of the system is designed in Solidwork, including the fixstructure of the optical element, the adjustment structure of measurement system, and theassembly of the entire system.4) Experimental verification and analysis of error sources: the method and principlewere proved correct and enforceable, and the error sources in the system were investigatedat last.Preliminary experimental results indicate that the system has high accuracy, and themeasurement deviation of curvature radius of simple lens is less than7ppm. The research inthis thesis provides an effective way to solve radius of curvature measurement problem forlens, which can meet the demand of high-precision metrology of large radius of curvature.