Research On The Key Technology Of Optical Element Shape Modification By Pulsed Ion Beam

As one of the existing technologies with the highest machining accuracy,ion beam figuring technology is usually the last process to improve the surface accuracy of optical components.At present,in the process of ion beam figuring,the acceleration of machine tool motion axis cannot meet the requirements of modification in some high-gradient error areas.In order to achieve the removal of different steepness errors,the machine tool motion with large acceleration and multiple replacement removal functions are usually used for iterative processing,resulting in excessive dependence on the dynamic characteristics of the machine tool and low efficiency in the processing of optical components,which cannot meet the use requirements.In view of the above problems,this paper starts from the beam extraction mode in the ion beam figuring process,and puts forward the pulsed ion beam figuring method,which can adjust the removal efficiency of the removal function with dynamic high frequency response.It is of great significance to reduce the dynamic performance of the machine tool and improve the precise control of the ion beam figuring residence time.The major research efforts include the following points:（1）Based on the requirements of optical element modification,the parameters of pulse power supply are calculated,and the stability and controllability of pulse power supply are developed and preliminarily verified.The key parameters of the pulse power supply are:the pulse frequency is 150 Hz,the pulse duty ratio is 0～100%and continuously adjustable,the pulse voltage is 0～1000 V,and the voltage stability accuracy is less than 0.5%,which can meet the needs of optical components figuring.Finally,the pulsed power supply is combined with the ion optical system to obtain a pulsed ion beam with the same pulse parameters as the pulsed power supply.（2）The key parameters of pulse ion beam removal function are analyzed theoretically,and the feasibility of error removal is verified.The mathematical model of pulse ion beam removal function is established,and the experiment proves that the spatial distribution of pulse ion beam removal function is Gaussian distribution.The fluctuation of the volume removal rate of the pulsed removal function is less than 0.6%within 48 min,which has good stability,and the pulse duty cycle has a linear relationship with the removal efficiency.At a pulse width of 0.01 ms,the material removal resolution is 6.7×10^-4nm,which is two orders of magnitude higher than that of continuous ion beam.In summary,pulsed ion beam is a stable high-resolution material removal tool with linearly adjustable removal efficiency,which can adjust the removal function in real time for high-efficiency error removal.（3）The key parameters of pulsed ion beam are modified and modeled,and the theoretical model of error removal about duty cycle and pulse frequency is established.The method of solving the pulse duty ratio matrix is proposed,and the pulsed ion beam figuring experiment is carried out.Under the condition of uniform motion of the ion source,the initial amplitude and frequency of the periodic error are respectively 23nm and 4.6mm^-1.After repairing,the amplitude of periodic error is decreased to 4.219nm.This result reduces the dependence of the modification process on the dynamic performance of the machine tool and also verifies the feasibility of the pulsed ion beam figuring.