【作者】 耿蕊；

【导师】 简水生；

【作者基本信息】 北京交通大学 ， 通信与信息系统， 2010， 博士

【摘要】 基于双包层掺杂光纤的高能超短脉冲激光系统损耗小、阈值低、效率高,易实现小巧、紧凑的结构设计,在国防、军事和工业加工等领域有着极其广泛的应用。如何进一步提高脉冲能量及功率是当前超短脉冲放大技术的研究重点。本论文对啁啾脉冲放大(CPA)技术与自适应脉冲整形技术结合实现超短脉冲的功率放大,以及光纤激光系统泵浦技术——激光二极管线阵的光束整形与耦合技术进行了深入的理论与实验研究,获得的主要创新成果如下：1.建立了一个基于双包层掺镱光纤放大器的自适应脉冲整形CPA系统模型,利用该模型,首次对CPA系统及放大器内自相位调制等超短脉冲功率放大的限制因素进行了分别补偿,并分析了补偿过程中自适应脉冲整形的作用机理。首次对比了相位整形、幅度整形及二者同时整形对输出脉冲功率提高的不同效果,理论上证明了幅度与相位同时调制的整形方式更有利于系统获得高质量、高能量的超短激光脉冲输出,分析了不同优化参数对补偿效果的影响,研究结果对实验系统的建立和调试具有指导意义。2.在理论分析的指导下,参与搭建和调试了一个自适应控制的CPA实验系统。该系统引入自适应脉冲幅度和相位同时整形实现了高功率超短激光脉冲输出,输出脉冲的平均功率高达12.6W,重复频率50MHz,脉冲宽度～170fs；系统将为智能中红外波段脉冲产生器提供激光脉冲源,整形后脉冲经光参量过程频率转换至中红外(mid-infrared:MIR)波长,产生可以自适应控制形状与特性参数的MIR超短脉冲,可用于分子的相干控制实验。3.建立了激光二极管线阵的非序列光学模型,并在此基础上设计了一种通过均衡线阵快慢轴方向光束参数积来提高光束质量的整形方案。该方法利用微型反射镜和平行六面体棱镜对光束进行准直、分割及重排,消除各发光区之间不发光间隔的影响,得到占空比为1的输出光束。整形后光束能量集中,亮度明显提高,经球透镜聚焦后更易与光纤耦合。4.提出了一种成本低廉、操作简单,材料与技术成熟、易于推广的微透镜制作方法,并用此方法制成了分别用于激光二极管线阵快、慢轴光束准直的透镜。研究结果表明,准直后光束消除了发光区间不发光间隔的影响,在水平和竖直方向上的光强度重新分布,光束质量和亮度得到大幅度的提高。5.提出了两种制作直径渐变型石英锥体的方法,拉丝法与氢氟酸腐蚀法；通过分析它们的动态过程,得出了各自的锥体直径随长度变化的关系曲线,与实测结果一致性较好。研究结果表明,腐蚀法制作的石英锥体与激光二极管线阵的耦合效率较高,可达76%。因此,利用其对光束的分束聚焦功能,可以实现激光二极管线阵对双包层掺杂光纤的侧面多点泵浦,这将极大地提高光纤激光系统的输出功率。更多还原

【Abstract】 Rare-earth-doped double-clad fiber based high-power and high-energy ultrashort pulses laser systems have been widely used in national defense, industrial processing and military due to their outstanding advantages in high efficiency and compactness. Thus, study on the enhancement of the energy and power of ultrashort pulses is really attractive currently. This dissertation is mainly devoted to the detailed theoretical and experimental researches on:adaptive pulse shaping techniques used for power amplification of ultrashort pulses in chirped pulse amplification (CPA) system, beam shaping of laser diode bars (LDBs), and methods of enhancing the pump coupling efficiency for LDBs with double-clad fibers. The main achievements of this thesis are listed as follows:1. A numerical model for Yb-doped fiber amplifier based CPA system with adaptive pulse shaping is found. With this model, several primary limiting factors in power amplification of the output pulses of the system are compensated respectively; meanwhile, the function of the adaptive pulse shaping in each compensation procedure is also illustrated in detail. For the first time, phase shaping, amplitude shaping and phase& amplitude shaping are compared with each other to verify their different influence on the power amplification, and different feedback parameters of the optimization algorithm are also compared for this purpose. This is of great importance for the setup and debugging of the experimental system.2. The generation of high-fidelity femtosecond pulses is experimentally demonstrated in a fiber based CPA system through an adaptive amplitude and phase pre-shaping technique. A train of pulses is produced with an average power of 12.6W at a 50MHz repetition rate from this fiber CPA system, which are compressible to high fidelity pulses with duration of 170 fs.3. A non-sequential optical model of laser diode (LD) bars is established with ZEMAX software, and a new beam shaping method for LD bars based on beam division and rearrangement by using parabolic reflective mirrors and parallelepiped prisms is optimized and verified with this model. Using this method, a rectangular shaped beam whose fill factor is 1 is obtained with more concentrated energy distribution and improved brightness.4. A compact beam collimator for LD bar is fabricated with a simple method. The fabrication is based on the using of fiber-drawing tower and silica. Theoretical and experimental results show that both the quality and the brightness of the collimated beam are greatly enhanced via the redistribution of intensity in the two axis directions and by eliminating the fill factor for the LD bar.5. Two methods of fabricating tapered SiO2 rods for beam concentrating are presented: using a fiber-drawing tower and utilizing the etching function of hydrofluoric acid. The dynamic procedures of these two methods are analyzed, and the predicted curves of the diameters of the SiO2 tapers versus their lengths are shown, which are of good consistency with the measured results. The simulation and experiment results show that, the taper fabricated in the latter way has a higher coupling efficiency when it is used for beam concentrating of the laser diode bar, which can be as high as 76%. Thus, it is possible to apply this taper in multi-points side pumping of the rare-earth-doped double-clad fiber, which will greatly enhance the output power of the fiber laser and amplifier systems.更多还原