Study On The Material Removal Mechanisms And Fundamental Processes For Ion Beam Figuring Optical Mirrors

The performance demands of the optics system increase with the development ofscience and technology. The developments of the optical observation system, laser weaponsystem and lithography system improve the requirement of the optics components, andthe technical requirements for optics components of these systems are improved comparedto conventional systems. Especially, modern systems need mirrors of large aperture, largerelative aperture, light-weighted, thin and o?-axis. The residual surface error of mirrorsused in these systems should be controlled within the full range (all spatial frequencycomponents of wavefront in the clear aperture of the mirror) strictly. How to manufactureoptics components of high precision with high e?ciency comes to be the key problem ofthe optics manufacturing to be settled. With the near-Gaussian removal function deducedfrom the ion sputtering mechanism, the low frequency errors of the optics mirror arecorrected according to the CCOS principle. The material removal is in the nanometerscale. Due to non-contact between the tool and the workpiece, the edge-e?ect and tool-wear problems involved in the conventional process are avoided. Ion beam figuring processis of high determinacy and of high e?ciency. All these properties make ion beam figuring beone of promising methods for mirrors of high precision. In order to form the fundament ofion beam figuring technology and process, this thesis is dedicated to solving key problemsin the material removal mechanism and surface error correcting technologies with theSigmund sputtering theory and CCOS principle. The major research e?orts include thefollowing points.1. The common problems about the removal function and shaping principle are deducedfrom the CCOS and Preston principle. Based on CCOS principle, the ion beammanufacturing system—KDIFS-500 is designed from the aspects of structure, functionand precision. With the DH kinematics model of KDIFS-500, the error transformingmodel is built. Based on the error model, the strategy of error compensation andcontrolling is presented, and the post-processing algorithm of KDIFS-500 is deduced.2. Based on the Sigmund sputtering theory, the relation models between the propertyfactors such as material removal e?ciency, disturbance depth and thermal e?ect andprocess parameters of the ion beam figuring are built. Simulation and experimentsare carried out to validate these models. With these discussions, the optimizationfundament of process parameter comes into being. Based on the abstract of ion beamfiguring process, the removal function models are built. The properties of the removalfunction are deduced from these models. Experiments are carried out to validate theseproperties. Based on the CCOS principle, the Hermite-Fourier model of the figuringprocess are built. With this double-series model, the e?ects of the removal functiondisturbance, measure error, positioning error and discrete interval on the figuringprocess are analyzed. These discussions form the fundaments of process parameter controlling strategy and the choice of process route.3. The relation among the roughness evolution of mirrors after ion beam bombardment,the energy of the incidence ion and the removal depth are analyzed with experiments.The characteristic microstructures of the sputtered surface are discovered. Combinedwith the sub-surface damage model during the conventional lapping and polishing,the cause for the roughness evolution is discussed.4. Based on the CCOS principle and the realization error model of the dwell time inthe approximated velocity mode, Bayesian-based iterative algorithm for planar mir-rors is deduced. The non-negativity of the iterative algorithm makes sure that thedeconvoluted dwell time be greater than zero, which is demanded in the figuring pro-cess. Based on properties of the removal function, the shaping process of low gradientmirrors can be approximated to be the linear model for planar mirrors. With thesediscussions, the unified error surface controlling technology for planar and low gradi-ent mirrors with full-aperture linear scanning mode is set up. By the circular averagedealt with the removal function, the figuring process with spiral scanning path canbe simplified to a linear one and be described by conventional CCOS principle. Withthe Bayesian-based iterative algorithm, the dwell time is deconvolued. The dwelltime is realized on a spiral path with varied rotative velocity. With these methods,the ion beam figuring technology with spiral scan mode comes into being. Based onCCOS principle, the finite field non-linear model is deduced from the stitching shapingmechanism. With the superposition property in the model, a modified Bayesian-baseiterative algorithm is presented to deconvolute the dwell time for the stitching process.The e?ect of the positioning errors and the removal rate on the machining accuracyand shape is modeled and then the identification and compensation algorithm forthese parameters is proposed based on this model. With these studies, the stitchingfiguring technology comes into being.5. With the discussions above, the unified ?ow chart for full-aperture linear scanningmode, polar scanning mode and stitching scanning mode is presented based on the con-ventional process. Figuring experiments on planar, spherical and aspherical mirrorsvalidate the e?ectiveness and correctness of the ?ow chart. With the closed loop con-trol technology provided by the process parameter"identification—compensation"step,the process e?ciency can be very high, which is the obvious character of the ?ow chart.