【作者】 王元虎；

【导师】 任德明；

【作者基本信息】 哈尔滨工业大学 ， 物理电子学， 2010， 博士

【摘要】 单纵模TEA CO₂激光器因其具有窄线宽、高功率、可调谐、对人眼安全等优点,广泛应用于光泵浦远红外激光器、分子光谱学、速度测量以及大气遥感监测等诸多领域中。当其用于CO₂差分吸收雷达（DIAL）时,由于具有极好的单色性和相干性,可以实现外差探测。与直接探测CO₂ DIAL相比,外差探测CO₂ DIAL探测距离更远,探测灵敏度更高,并且可以同时获得目标的速度信息,这些优点使得国外在二十世纪八十年代就开始对其进行研究。外差探测CO₂ DIAL的关键技术之一就是要求使用频率稳定的单纵模TEA CO₂激光器,作为发射机的振荡源,鉴于此,本文从理论上和实验上对TEA CO₂激光器获得单纵模激光技术及频率锁定技术进行了研究。首先导出了可以描述TEA CO₂激光器动力学过程的六温度振动转动模型,利用该模型对单纵模TEA CO₂激光器的输出特性进行了分析,讨论了混合气体压强、气体成分、气体温度、输出耦合镜反射率以及谐振腔长对输出激光的影响,为TEA CO₂激光器的优化设计提供了理论依据。研制了一台高重复频率可调谐TEA CO₂激光器。对激光器的电极面型、预电离方式以及放电电路进行了分析和计算,建立了CLR放电电路的理论模型,并且根据激光器实际工作参数利用该模型对放电过程进行了模拟,揭示了气体激光器脉冲放电的规律。当激光器单横模运转时,可获得四个谱区共77支谱线的调谐输出,最强支谱线基横模输出能量达到350mJ,M²=1.21。为了获得较大范围内单纵模激光的高功率可调谐输出,提出一种多干涉仪谐振腔结构。从三镜腔实现单纵模激光的机理出发,基于场方程和自洽场理论,对采用多干涉仪谐振腔获得单纵模激光的特性进行了分析和计算,讨论了影响激光器选单纵模能力的因素。实验上采用这种谐振腔结构实现了TEA CO₂单纵模激光的输出,得到10.6μm单纵模激光最大输出能量为324mJ,激光器可以实现69支谱线单纵模激光的调谐输出。在相同的实验条件下,与其它的干涉型谐振腔相比,使用多干涉仪谐振腔得到的单纵模激光的能量和调谐范围均有较大提高。为了实现稳定的单纵模激光的快速调谐输出,进行了快调谐TEA CO₂激光器注入锁频技术的研究。理论上将六温度振动模型与注入场方程耦合,考虑转动动力学及谐振腔模式间的相互作用,得到了注入锁频TEA CO₂激光器的理论计算模型,并采用此模型计算了不同条件下注入锁频激光器的输出特性。实验上首先采用扭转模腔实现了弱支谱线单纵模激光的输出,9.77μm单纵模激光的输出能量达到47mJ,有效地解决了TEA CO₂激光器中增益较弱谱线单纵模难以稳定输出的问题,同时也为注入锁频奠定了基础。然后通过缩短激光脉冲建立时间的方法来控制连续种子激光器与脉冲激光器之间实现纵模匹配,实现了TEA CO₂激光器的注入锁频,并对频率锁定时和失锁时输出激光的特性进行了研究。最后设计了一种新型的快调谐机制,解决了激光器快调谐输出时的重复定位精度问题,并且利用这种方法实现了10.28μm锁频激光和9.77μm单纵模激光的快调谐输出。更多还原

【Abstract】 On account of the advantanges including narrow linewidth, high power, tunable, eye-safe, etc., single longitudinal mode （SLM） TEA CO₂ laser is of special interest in areas such as optically pumped far-infrared lasers, molecular spectroscopy, velocimeters and remote sensing of the atmosphere. SLM TEA CO₂ laser can be used in heterodyne differential absorption lidar （DIAL） system because of its excellent monochromaticity and coherency. Compared with direct detection CO₂ DIAL, heterodyne detection DAIL has longer detection range and higher sensitivity. The velocity information can be acquired at the same time. Such kind of research has been conducted for a long period in many foreign institutes. In the heterodyne detection CO₂ DIAL system, both power and frequency of the laser have to be stabilized. In view of this condition, the technologies to obtain SLM TEA CO₂ laser and frequency locked laser have been investigated theoretically and experimentally in this dissertation.First of all, a six temperature vibrational-rotational model has been used to analyze the kinetic process of TEA CO₂ laser. Output characteristics of the laser were investigated according to the model. The influences of gas pressure, gas mixture ratio, gas temperature, reflectivity of output coupler and cavity lengths on the output laser have been researched, respectively. The six temperature vibrational-rotational model will be contributed to the optimized design of TEA CO₂ laser.A tunable TEA CO₂ laser has been designed. The electrode style, preionization and discharge circuit of TEA CO₂ laser were analyzed and calculated. A numerical model of the discharge circuit was established to simulate the discharge process of the laser. When the laser operated in single-transverse mode, 77 emission lines of the CO₂ molecule rotational transition is obtained. The maximum energy of 350mJ and M²=1.21 are obtained when the laser operated in fundamental transverse mode.In order to obtain high power SLM laser and expand the tuning range, a multi-interferometeric resonator has been presented. Based on the principle of SLM oscillation obtained by using a three-mirror resonator, a numerical model of the interferometric resonator is investigated to optimize the laser for mode selection based on self-consistent wave method and a stochastic method. SLM operation has been theoretically predicted using the model. Experimentally, SLM TEA CO₂ laser oscillation is realized using multi-interferometeric resonator. When the laser operated in SLM, 69 emission lines of the CO₂ molecule rotational transition is obtained. Pulse output energy of 324mJ at 10.6μm has been obtained. In the same experiment conditions, it shows that this multi-interferometric resonator gives better performance in mode selection than other resonator based on multi-beam interference. Both the output energy of SLM laser and tuning range can be improved obviously using this configuration.To achieve rapid tuning in a stable SLM TEA laser, the injection locking technique of rapidly tunable TEA CO₂ laser has been researched. Theoretically, considering vibrational kinetics of TEA CO₂ laser and interaction between resonator modes, a numerical model has been developed to represent the kinetics of injection locked TEA CO₂ laser by combined six-temperature model of vibrational kinetics with injected photon field equation. Output characteristics of the laser have been calculated and analyzed in different condition. Experimentally, a twisted mode cavity has been used to obtain SLM TEA CO₂ laser with weak-gain. SLM output energy of 47mJ is obtained at 9.77μm. This method can solve the problem that stable SLM TEA CO₂ laser of weak-gain is difficult to obtaine and it lays the foundation of injection locking. Then frequency locking of the TEA CO₂ laser has been obtained. Mode matching between the seed laser and the pulse laser has been achieved by shortening built-up time of the pulse. The characteristics of output laser have been investigated both in the situation where laser frequency was locked and not. Finally, a novel rapid tuning mechanism has been presented to improve repetitive positioning accuracy when the laser achieved rapid tuning. Using this mechanism, the rapidly tunable output between frequency locked laser at 10.28μm and SLM laser at 9.77μm has been realized.更多还原