| 题名 | 改善激光二极管阵列光束质量和光谱特性的关键技术研究 |
| 作者 | 苏宙平 |
| 学位类别 | 博士 |
| 答辩日期 | 2008 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 楼祺洪 |
| 关键词 | 激光二极管阵列 外腔 束宽积 光谱线宽 激光亮度 光谱功率 |
| 其他题名 | Researches on improvement of spatial beam quality and spectral characteristics of laser diode bar |
| 中文摘要 | 高功率激光二极管阵列,由于其结构紧凑，价格低廉，操作简单以及比较高的效率和较长的使用寿命在工业应用医疗领域以及科学研究等得到广泛的应用。但是激光二极管阵列的典型的线宽2-4nm ，且光束质量较差。这使许多应用得到了限制。改善高功率激光二极管阵列的光束质量常用的方法是各种各样的整形技术，然而整形技术往往都是通过降低了快轴方向的光束质量而提高慢轴方向的光束质量。因此，输出激光的亮度没有几乎什么变化。本文采取了外腔反馈的技术来不仅能有效地改善激光二极管阵列慢轴方向的光束质量，而且能够提高输出激光的亮度。运用外腔反馈的技术也实现了窄线宽的激光输出。 第一章 综述了半导体激光器的发展历史和现状以及半导体激光器在各 个领域的应用。分析了改善半导体激光光束质量的必要性，重点介绍了用于改善半导体激光光束质量的各种各样的光束整形技术和外腔反馈技术。同时，对改善大功率半导体激光器光谱线宽的研究现状也进行了综述。 第二章 介绍了半导体激光器的结构、特性、空间模式理论和纵模理论。采用解析微扰模型计算了单个激光二极管的“阵列模”，分析了其远场分布的精细结构和特征，其远场分布的一个主要特征是一个双瓣结构。根据“阵列模”理论，推导激光二极管阵列的“组合模”，计算其近场分布和远场分布。此外，对半导体激光的纵模理论也作了详细介绍。 第三章 设计了一种离轴外腔的装置来改善激光二极管阵列的慢轴方向的光束质量。外反馈的元件是平面高反镜，反馈元件能够选择阵列的各发光单元具有相同辐射角的空间模的一个瓣注入到激光二极管的增益区，另一个瓣作输出。使用这一装置，在工作电流为18A时，输出激光的束宽积从自由运转时的1415mm.mrad 减小到了331mm.mrd. 将一个空间滤波器插入到外腔中，优化滤波器的尺寸和位置，使输出激光的束宽积减小到238mm.mrad。激光二极管阵列在自由运转时输出功率为4W,使用外腔反馈时输出功率为3.24W,插入空间滤波器后输出功率变为2.8W。与自由运转情况下相比，尽管输出功率有所损失，采用外腔结构以后，激光亮度分别提高了14.8和24.7倍 第四章 研究了激光二极管阵列的谱线窄化技术。在驱动电流15A时，采用Littrow和Littman-Metcalf外腔反馈技术，输出线宽从自由运转情况下的2.2nm分别减小到0.15nm和0.16nm。在Littrow外腔反馈实验中，转动光栅，在恒定温度下，实现了从807-818nm范围的调谐。分析了外腔反馈影响谱线展宽的因素：慢轴方向的发散角和二极管阵列的排列弯曲（即“smile”效应）。为了改善“smile”效应引起的谱线展宽，设计了一种双镜反馈的Littman-Metcalf外腔。在驱动电流15A，双镜反馈的Littman-Metcalf外腔，获得了输出线宽为0.1nm 的激光。 第五章 设计了一种双路反馈的外腔装置，可以同时来改善输出激光光束质量和光谱线宽。两路的反馈元件分别是衍射光栅和平面高反镜。运用这种装置，在工作电流18A时，输出激光的谱线宽度被压缩到0.26nm, 束宽积被减小到317mm.mrad，与自由运转时相比，光谱线宽和束宽积分别提高了7.6倍和4.4倍。当改变激光二极管阵列的热沉温度时，自由运转输出激光的中心波长呈线性变化，而带有外腔的输出激光中心波长几乎没有变化。使用双反馈外腔以后斜率效率从自由运转时的0.9W/A 降低到了0.39W/A。在工作电流18A时，双反馈外腔输出功率为自由运转时的58%，然而它的光谱功率和激光亮度比自由运转时分别提高了4.4倍和11.5倍。 |
| 英文摘要 | Due to their compactness, low cost , excellent efficiency and long operational lifetime, high-power laser diode bars (LD bar) or stacks (LD stack) are attractive laser sources for many applications such as industry, medicine, science research and so on. However, the spectral bandwidths of LD bar are generally approximately 2-4nm. Also, the spatial beam quality is very poor. The poor spatial beam quality and bandwidth are still limiting factors for many applications. Various beam-shaping techniques have been developed to improve beam quality of LD bar in slow axis direction. However, the beam-shaping techniques can not improve the laser brightness of LD bar. In this dissertation, by employing external cavity feedback techniques, not only the beam quality of LD bar in slow axis but also laser brightness of LD bar have been improved drastically. Also, bandwidth-narrowed, tunable laser output is obtained by using external cavity feedback techniques. In the first chapter, the history and current status of laser diode are demonstrated. Some important applications of laser diode are also presented. The importance of spatial beam quality improvement of laser diode is reviewed. Various beam shaping techniques and external cavity feedback techniques for improving beam quality of laser diode are introduced in detail. In addition, research progress on spectral bandwidth reduction of laser diode is also overviewed. In the second chapter, devices constructures, performances, spatial and longitude modes theory of laser diode are introduced in detail. An analytical perturbation model is presented to calculate the “array mode” of broad-area laser diode. Near-and far-field patterns of “array mode” are calculated and near-and far-field fine structures and characteristics are analyzed. The “array mode” has a twin-lobe profile in the far field. According to the “array mode” theory, the “combined mode” of laser diode bar is derived and near-and far-field patterns of “combined mode” are calculated. In addition, the longitude mode theory of laser diode is also introduced. In the third chapter, an off-axis external cavity setup is designed to improve beam quality of laser diode bar in slow axis direction. The common feedback element shared by all emitters is a plane mirror with high reflection coating. For each emitter in bar, due to the different radiation angles of various spatial modes, a single lobe of one of the spatial modes may be chosen by adjustment of high-reflective mirror tilt. The selected lobe of this mode is feedback into the laser diode, the other lobe of this mode is amplified and coupled out of the external cavity as output beam of laser system and all the other modes are suppressed effectively. By employing the techniques, the BPP is reduced to 331mm.mrad from 1415mm.mrad of free-running laser. When a spatial filter is placed in the external cavity with the optimal size and location, the BPP is reduced to 238mm.mrad. At the driver current of 18A, the output power of free-running laser is about 4W and the output power of external cavity feedback laser diode(ECLD) bar without and with spatial filter is 3.24W and 2.8W respectively. In spite of power loss, the output laser brightness of ECLD bar without and with spatial filter is improved with a factor of 14.8 and 24.7 respectively. In the fourth chapter, Littrow and Littman-Metcalf external cavities are designed appropriately to narrow linewidth of laser diode bar. By employing the Littrow and Littman-Metcalf external cavities , the linewidth is reduced to 0.15nm and 0.16nm respectively at drive current of 15A. In Littrow external cavity setup, 11nm of tuning(807-818nm) can be obtained by rotating grating at 23oC heat sink. In the external cavities, the line-width broadening effect is caused mainly by divergence in slow axis and array curvature (also “smile” ). An improved Littman-Metcalf external cavity with two mirrors is designed that can reduce the contribution of “smile”to line-width. By employing the technique, the linewidth is narrowed to 0.1nm at drive current of 15A. In the fifth chapter, an external cavity setup with double feedback braches is designed to simultaneously improve the spectral and spatial properties of the LD bar. The feedback elements are blazed grating and high-reflection plan mirror. By using the setup, the spectral bandwidth is narrowed to 0.26nm and the BPP is reduced to 317mm.mrad.Compared with the bandwidth and BPP of free-running laser, the spectral bandwidth is narrowed 7.6 times and the BPP is reduced 4.4 times. Changing heat sink temperature of LD bar, the center wavelength of free-running laser is changed almost lineally, however, the center wavelength of laser with double feedback external cavity almost keep unchanged. The slope efficiency falls to 0.39W/A from 0.9W/A, when double feedback external cavity is applied. At the driver current of 18A, the output power is as much as about 58% of free-running state power. However, the spectral power and laser brightness are improved 4.4-fold and 11.5-fold respectively. |
| 语种 | 中文 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15239]  |
| 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 | 苏宙平. 改善激光二极管阵列光束质量和光谱特性的关键技术研究[D]. 中国科学院上海光学精密机械研究所. 2008. |
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