Studies On Large Aperture Discharge Of TEA CO₂ Laser

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.