【作者】 郭琦；

【导师】 吕志伟；

【作者基本信息】 哈尔滨工业大学 ， 物理电子学， 2010， 硕士

【摘要】 重复频率、高功率、大能量的激光可以广泛地应用于军事、科研和工业等领域。单束激光器能量的增加存在着不可避免的限制,因此现在的大能量激光系统往往工作在单次状态,难以达到重复工作的要求。如何获得高重复频率、高功率、大能量的激光输出一直是科技界关心而又难以解决的问题。激光组束,由于其使单路激光运转在小能量、低功率的状态下,避开了单路激光在增加激光能量和功率方面的诸多限制,成为了获得大能量、高功率激光的有效途径之一,受到了人们的广泛关注。目前激光组束的研究虽然已经发展了很多种方案,但是都没有达到实用的水平。SBS激光串行组束基于布里渊放大的原理,利用一束Stokes光逐级抽取泵浦光束中的能量,可使多束光的能量向一束光转移,最终实现多束激光的合成输出。SBS激光串行组束是一种完全相干组束,获取的输出激光束在物理上是单束光,且系统可升级性高。本文首先从SBS的经典理论出发,建立了SBS激光串行组束的物理模型。运用共线布里渊放大的模拟程序,研究了系统各参数——泵浦参数、结构参数、介质参数等,对共线强信号布里渊放大的能量提取效率及光束质量的影响,并进行了实验验证。实验上,在泵浦光与Stokes光能量比为39.5:1时,可达到400mJ的输出能量,获得80%以上的能量提取效率。泵浦光的主要作用是提供能量,而输出光的光束质量主要由Stokes光决定。其次,对非共线布里渊放大中的相位匹配进行了研究。从理论上分析了非共线布里渊放大效率下降的主要原因,即Stokes光与泵浦光的夹角造成的波矢失配。给出波矢失配对布里渊放大的影响,并提出用控制放大介质频移的方法来消除波矢失配,并进行了实验验证。论文最后给出了SBS激光串行组束系统的设计,采用共线结构单元与非共线结构单元相结合的思想,并给出其中共线结构单元与非共线结构单元的设计依据。更多还原

【Abstract】 High-power/energy laser with a high repetition rate is widely used in several subjects, such as inertial confinement fusion, material processing and so forth. However, high thermal load and the crystal-growth volume constraint the development of higher energy solid state laser system. Therefore, the method to obtain a high-power/energy laser with a high repetition has been a focus of research recently. The beam combination is a promising method in overcoming these problems by dividing one laser beam into several beams and recombined after separate amplification.In the beam combination system, stimulated Brillouin scattering phase conjugate mirrors (SBS-PCM) are always used as reflectors because the thermal distortion in the active media could be compensated by the phase conjugate waves. However, none of these systems can overcome the limit of high load and complexity of structure. In order to obtain a reasonable high power/energy laser, a method of serial coherent laser beam combination is approached, which is based on the theory of Brillouin amplification.Firstly, a general mathematical model of SBS serial laser combination was constructed from the classic coupled-wave equation of SBS. By using of collinear Brillouin amplification model, the relationship between the parameters of system and the energy extraction efficiency of strong seed Brillouin amplification is provided. In experiment, output energy of 400 mJ and energy extraction of 85% are achieved when pump energy is 10mJ and energy of Stokes and pump beam is in the ratio of 39.5 to 1, and the conclusion that the quality of output beam is controlled by Stokes beam is drawn.Secondly, phase match in non-collinear Brillouin amplification is investigated. The reasons that cause the decrease of energy extraction efficiency are analyzed. It is indicated that mismatch of phase, which results from the crossing angle between Stokes and pump beam, is the major cause. A method of changing the Brillouin frequency shift of medium is approached to eliminate the mismatch of phase.Finally, the design of SBS serial laser beam combination system is provided, which employs a composite structure with collinear and non-collinear cells.更多还原