Study On The Key Technology For Efficient Machining Of Fused Silica Using Atmospheric Inductively Coupled Plasma

Fused silica optical materials are widely used in modern optical systems such as lithography machines,laser weapon system and inertial confinement fusion technology devices because of their excellent radiation resistance,chemical stability,ultraviolet permeability,and high threshold of intrinsic laser damage.Due to the characteristics of high hardness and poor brittleness of fused silica materials,surface and sub-surface damage can easily occur during the manufacturing of fused silica optical components.It is difficult to completely remove the damage introduced by the grinding and lapping process of fused silica elements in the traditional iterative mechanical damage by the method of reducing the damage thickness of layer by layer,and it is also difficult to meet the increasing demand of fused silica optical elements because of the low machining efficiency and high cost.Therefore,many researchers are focused on finding methods that can achieve non-damage and high efficiency machining.Atmospheric inductively coupled plasma machining,as a chemical-dry etching process,can achieve non-damaged and efficient machining of fused silica optical components.However,in the machining process of fused silica,the thermal effect of plasma will affect the intensity of the chemical etching reaction,and inevitably causes the non-linearity of material removal rate,which makes it difficult to achieve efficient deterministic machining of fused silica optical components.Based on the in-depth analysis of plasma heat generation and transfer and the formation of surface temperature distribution,this thesis explores the strategies of suppressing or weakening local heat effect and global heat effect in order to realize the efficient machining of fused silica optical mirror.The main research contents are summarized as follows.?1?Atmospheric inductively coupled plasma machining mechanism of fused silica is studied.Through the analysis of atmospheric inductively coupled plasma excitation theory and surface dynamics process,it is concluded that plasma is generated by collision of electrons with Ar and SF₆ gas molecules,and temperature rise can improve the probability of active particle generation.It is found that the high activation energy can strengthen the surface ion action,which makes the chemical reaction easier.Within a certain range,heating can help to improve the machining efficiency.However,temperature is also the key factor to the non-linearity of the removal rate of fused silica material in atmospheric inductively coupled plasma machining.?2?Local thermal effect of fused silica by atmospheric inductively coupled plasma machining is investigated.The energy balance process of inductively coupled plasma fused silica machining is analyzed.The time-varying non-linearity of the removal function caused by the local thermal effect in the efficient surface figuring process of atmospheric inductively coupled plasma is studied by line scanning experiment method.An experimental model of the time-varying non-linearity of the removal function is established by experimental method.A nested pulse iteration algorithm?NPIM?is proposed to solve and compensate dwell time accurately.The dwell time after compensation and adjustment is used to fused silica surface figuring experiments.The high efficient surface figuring of fused silica under local temperature effect is realized.?3?Global thermal effect of fused silica by atmospheric inductively coupled plasma machining is investigated.In the machining process,the global heat effect is becoming more and more prominent with the increasing diameter of fused silica components.Based on the analysis of Gauss heat source and linear heat source of atmospheric inductively coupled plasma,the temperature distribution on fused silica surface during the atmospheric inductively coupled plasma machining is mainly analyzed.At the same time,the static and dynamic temperature fields in the process of machining were studied,and it was found that the material removal in the scanning path was not uniform due to the global thermal effect of inductively coupled atmospheric plasma.Then,the effect of global temperature effect on the machining is balanced by using the round-trip nested grating tool-path,and the surface figuring of fused silica mirror under the influence of global thermal effect is realized.?4?The evolution of grinding and lapping surface of fused silica during atmospheric inductively coupled plasma is studied.The generation and detection methods of grinding and lapping damage are analyzed.The ability of removing fused silica damage efficiently by atmospheric inductively coupled plasma is verified by experiments of scratch removal and evolution of medial and lateral cracks.The ground and lapped fused silica surface is efficiently machined by atmospheric inductively coupled plasma.In this paper,the mechanism and key technology of atmospheric inductively coupled plasma for efficient machining of fused silica are studied.The efficient fabrication of fused silica optical components is realized.It provides rapid efficient manufacturing technical support for the growing demand of fused silica optical components in modern optical systems.