激光二极管泵浦的全固态板条激光器关键技术研究
文献类型：学位论文
| 作者 | 程小劲 |
| 学位类别 | 博士 |
| 答辩日期 | 2007 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 王之江 |
| 关键词 | 激光二极管 板条激光器 热效应 寄生振荡 薄片激光器 |
| 其他题名 | Study on diode pumped all solid-state slab Laser |
| 中文摘要 | 板条激光介质在纵横比值大于2时，能得到优于棒状激光介质的吸收热量能力。因此，设计合理的板条激光器可达到更好的光束质量和更高的输出功率，理论上它仅受激光介质断裂极限的限制。本文针对板条激光介质的特点，重点研究了板条激光器的热效应以及板条放大器的寄生振荡现象，并将热效应的计算方法推广到光子晶体光纤中。在此基础上，完成了一台百瓦级板条激光器的研究，并介绍了一台50W的薄片激光器的设计过程及目前的实验进展。 热效应是固体激光器不能回避的一个重要问题，激光介质因吸收了泵浦辐射而发热，而散热又要求对其表面进行冷却，这使得激光介质内部产生不均匀的温度梯度，而温度梯度的存在会导致热应力和热致折射率的变化，从而导致激光光束的产生热畸变。因此如何尽可能减小激光介质内的热效应是提高光束质量和输出功率所必须面对的一个问题。我们以Nd:YAG为激光介质，从热传导方程出发，使用Gauss-Seidel数值计算方法，对部分泵浦的板条激光器的温度分布、热应力和热致折射率变化等热效应进行了详细分析，并与单侧泵浦及双侧泵浦方式进行了比较。结果表明，设计合理的部分泵浦的板条激光器，可以获得较高的泵浦效率，其热效应相比于均匀泵浦的情况并没有显著地劣化，不论是采用Zigzag方式还是直线传播方式的激光器都可以获得较好的光束质量，当一束高斯激光直线经过板条晶体中部时，光束质量因子M2=1.4，若采用Zigzag传播方式，则光束质量因子可提高到M2=1。结合分形理论，我们将板条晶体热效应的计算方法推广到光子晶体光纤中，分析了空气包层的光子晶体光纤的热效应。 主振荡器-功率放大器结构（MOPA）是获得高功率高光束质量的激光输出一种有效方法。但自发辐射（ASE）的存在使得放大器工作介质会在信号光到达前开始发射激光，并且工作介质边缘的内反射能显著增大ASE的发射，尤其当这些反射能导致产生封闭路径时更是这样，当激光介质内的增益超过损耗时，就建立起寄生振荡。对于放大器而言，寄生振荡的存在使得激光介质在信号光到达之前就消耗了大量的反转粒子数，降低了晶体的峰值增益和存取效率，影响了激光放大器尤其是高功率激光放大器的性能，因此研究如何消除激光器工作物质内的寄生振荡对提高激光器的功率有着很重要的意义。我们结合实验研究，分析比较不同表面处理和泵浦条件下工作介质的放大效果，解决了侧面泵浦的板条晶体的寄生振荡问题。 薄片激光器可以允许介质具有高的抽运功率密度而不产生显著的热效应，当抽运区尺寸远大于薄片厚度时，热流可认为是沿厚度方向的一维分布，合理设计抽运耦合结构，可以使薄片宽度方向温度分布近似均匀，从而大大降低介质的热透镜效应和热致应力双折射。因此薄片激光器可以定标放大到很高的平均功率。我们在本文中介绍了一台50W薄片激光器的设计步骤及目前的实验进展情况。 |
| 英文摘要 | While the aspect ratio of the slab is greater than 2, a superior power handling capability relative to a rod can be obtained. If slab laser designed reasonable, better beam quality and higher output power can be obtained. Theoretically, the highest output power is limited by stress fracture limit. In this paper, thermal edffect in slab laser and parasitic oscillation in amplifier are analysized.Using the same method, we also calculate thermal effect in photonic crystal fibers (PCFs) with hollow claddings. Based on theory analyse, we completed a slab laser which output power is nearly 300W with master oscillator and power amplifier (MOPA). And a 50W thin slab laser is also introduced. Thermal effect is a serious problem in solid-state lasers. The combination of volumetric heating of the laser material by the absorbed pump radiation and surface cooling required for heat extraction leads to a nonuniform temperature distribution in the slab. So efficient heat removal, and the reductions of thermal effects usually dominate design considerations for high average power systems. Based on the heat conduction equations and the Gauss-Seidel numerical method, the distribution of temperature, thermal stress and thermally induced refractive index in partially pumped slab lasers is analyzed in comparison with single- and double-side pumped configurations. It has found that a partially pumped slab laser designed appropriately does not suffer more thermal distortion than that in the uniform pumped ones, meanwhile maintaining high pumping efficiency. Whether the laser works in zigzag or straightforward path, good beam quality can be achieved. If Gauss beam passes the centre portion of the crystal in straightforward path, the beam quality factor M2 is 1.4. If in zigzag path, M2 is 1.1. Master oscillator power-amplifier (MOPA) is efficitive method to gain both high output power and high beam quality. But internal reflections an the boundaries of active medium can drastically enhance the onset of ASE, particularly if these reflections lead to a close path, i.e., a ray that is reflected upon itself. In the case, we have a strong feedback mechanism and as soon as the gain in the laser medium exceeds the reflection losses parasitic oscillations will set in. Existence of parasitic oscillation makes the amplifier consume lots of population inversion before arrival of the signal pulse, reducing peak gain and storage efficiency and influencing amplification performance greatly, especially for high power amplifiers. By pumping Nd: YAG slab with 8 laser diode arrays, parasitic oscillation in high power amplifier is researched both theoretically and experimentally. The parasitic oscillation in the slab with different surfaces treatment is compared. When the pump energy is 1.28 J and the input pulse energy is 140 mJ, the single-pass amplification of =2 and the output pulse energy of 278 mJ is obtained. Thin slab laser cann’t produce obvious thermal effect with high pump power density. While the size of pump area is much large than the thickness of thin slab, the heat flux can be considered to be one-dimensional. So thin slab laser with design properly can reduce the thermal lens and thermal induced birefringence. In this paaper, we introduce detailedly the procedure of a thin slab laser which output power is 50W. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15537]  |
| 专题 | 上海光学精密机械研究所_学位论文 |
| 推荐引用方式 GB/T 7714 | 程小劲. 激光二极管泵浦的全固态板条激光器关键技术研究[D]. 中国科学院上海光学精密机械研究所. 2007. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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