【作者】 陈钰琦；

【导师】 程祖海； 左都罗；

【作者基本信息】 华中科技大学 ， 物理电子学， 2008， 博士

【摘要】 高能脉冲CO₂激光器由于近年兴起的激光推进、激光强场物理等应用的需求,又一次得到了人们的重视。实现稳定、均匀的大体积放电,是获得高单脉冲能量的必经途径。本文较为详尽的论述了在大放电体积下TEA（Transversely Excited Atmospheric）CO₂激光器的放电理论与实验研究结果。主要从放电电极、预电离方式、放电电路、放电发展过程和放电发光光谱分析出发,旨在优化放电结构,提高高气压大体积下的放电稳定性。从理论上对TEA CO₂激光器的均匀场放电电极进行了研究。利用有限元计算方法,计算并讨论了均匀场电极中电极面型、电极板安装结构和电极板厚度对实际电场分布影响。根据放电等离子体辉光分布,我们认为电极表面的电场强度分布,仅对放电的初始发展具有影响,而放电区中央的电场分布以及预电离强度,对最终放电区的均匀性具有决定性的影响。对影响小信号增益的各种因素进行了实验研究。系统地讨论了电路因素（放电区结构、放电电路、充电电压等）和非电路因素（气体成分、工作气压、种子气体等）对小信号增益的基本影响规律。从预电离技术和均匀场电极方面综合考虑,对预电离结构进行了优化。比较了多种电极和预电离结构组合的放电效果,其中采用近罗可夫斯基电极和紧密排列火花针预电离的组合方式能够获得更宽的放电区域和更高的小信号增益。使用放电电压、电流波形以及放电区小信号增益系数作为评价手段,对Marx高压脉冲发生器放电电路进行了实验分析和改进。实验研究发现,储能相同的条件下,Marx高压脉冲发生器的结构和参数能极大地影响注入效率。在放电电路中采用峰值电容提高了初始预电离强度,最佳峰值电容与储能电容比为Cp/Cs=0.075。最终采用的单级储能电容为0.5μF的电阻隔离型三级Marx高压脉冲发生电路,对无氦工作气体,小信号增益系数最大可达3.2%cm^-1。为了了解放电的微观发展过程,利用ICCD相机对脉冲CO₂激光器的放电区进行观测,获得了完整的放电辉光时空发展过程,并且利用发射光谱法对TEA CO₂激光器放电致等离子体发光光谱进行了诊断。从实验结果来看,TEA CO₂激光器中放电辉光强度、等离子体发射光谱强度和放电电压波形之间存在对应关系,都随放电电压波形而同步变化。根据测得的氮分子第二正带系发射光谱的顺序带组进行了等离子体的振动温度的拟合和计算,所得的振动温度范围在3300K～4100K之间。利用本论文的研究成果,成功实现70mm和100mm放电间距的高气压稳定放电。采用电感镇流紧密排列火花塞预电离技术,近似Rogowski-Ernst混合电极,在4L的放电体积里,最大单脉冲能量达到了169J的水平。更多还原

【Abstract】 Recently,studies on high power pulsed CO₂ laser become active again due to the newly growing applications such as laser propulsion and opto-electronic countermeasures. Stable and uniform large aperture discharge is the key technology to obtain high pulsed energy.In this dissertation,the theoretical and experimental results of large aperture discharge are discussed in detail.In order to optimize discharge configuration and obtain stable large aperture discharge,the effects of electrode profiles,preionization methods,discharge circuit have been studied respectively.Firstly,the uniform-field electrode of TEA CO₂ laser is analyzed theoretically.The effects of electrode profile,thickness and installing structure on the distribution of electric field are calculated and discussed.Compared with the discharge photos,it can be concluded that the initial development of discharge may be influenced by the distribution of electric field on the electrode surface,while the uniformity in the whole pulsed discharge process mainly depends on the distribution of electric field on the central area and the preionization.Secondly,the factors influencing small signal gain performance of TEA CO₂ laser are studied experimentally.The effects of discharge zone configuration,discharge circuit,gas composition,pressure and additives on small signal gain have been obtained.Thirdly,considering both preionization method and electrode profile,the preionization configuration is optimized.The discharge characteristics of several combinations of electrode and preionization are compared,in which the combination of plate-arc electrode and dense spark preionization show the best performance.Then,the modification of pulse discharge circuit is studied experimentally to improve the discharge and gain performance.It reveals that with the same storage energy,the parameters of Marx high voltage pulse generator circuits have an important influence on the injection efficiency.Using peaking capacitor can improve the initial preionization strength, the optimized ratio of peaking capacitor to charging capacitor is 0.075.The discharge circuit of resistance-isolated three-stage Marx high voltage pulse generator with 0.5μF capacitance each stage gives good results.When helium-free gas mixture is used,the highest small-signal gain coefficient reaches 3.2%cm^-1.In order to obtain the microcosmic development of discharge,time-resolved photos of discharge plasma taken by ICCD camera are analyzed.Quantitative data on the spatial and temporal development of glow discharge are given.The emission spectra of discharge plasma are also measured and analyzed.It reveals that the intensity of discharge glow and the intensity of emission spectra are correspondent with the waveform of discharge voltage, they are both variable with the change of discharge voltage.Through the analysis of the second positive system of N₂,the vibrational temperature is calculated by sequence band method.The vibrational temperature varies in the range from 3300 K to 4100 K.Finally,applying the research results obtained in this thesis,stable discharge is established successfully in the discharge zone with the aperture of 70 mm and 100 mm.For a discharge construction with plate-arc electrode and dense spark preionization,169 J pulse energy was obtained from a discharge volume about 4 L.更多还原