高功率激光小尺度自聚焦和光束匀滑技术研究
文献类型：学位论文
| 作者 | 张艳丽 |
| 学位类别 | 博士 |
| 答辩日期 | 2009 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 朱健强 |
| 关键词 | 小尺度自聚焦 发散光束 最大增益 最大增长频率 光束匀滑技术 |
| 其他题名 | Research on Small-scale Self-focusing and Beam Smoothing in High Power Laser |
| 中文摘要 | 高功率激光驱动器装置中不仅要求有非常高的脉冲功率，好的近场光束质量，而且对激光远场的均匀性也有十分苛刻的要求。因而如何提升激光功率，控制光束质量和改善靶面辐照均匀性一直是高功率激光驱动器装置中非常重要的研究内容。非线性折射率引起的光束小尺度自聚焦是限制高功率激光输出功率和使光束质量变坏的主要因素之一,研究小尺度自聚焦的传播规律及其抑制方法是提高激光输出功率和近场均匀性的关键，其中，发散光束由于存在发散的波面，有助于抑制小尺度自聚焦。鉴于小尺度自聚焦对近场光束质量的影响，寻求强度和位相畸变宽容度大的光束匀滑技术显得比较重要，且为了达到很好的匀滑效果，实际中常采用的是空间匀滑技术和时间匀滑技术相结合的有效方式。本文围绕小尺度自聚焦传输特性和靶面辐照均匀性两方面问题，主要完成了以下几个方面的理论研究工作： 1. 利用分步傅立叶变换方法，数值模拟了两种初始条件下光在非线性介质中传输的特性，计算结果显示，平面波的小尺度调制增长与传播距离呈指数关系，调制相隔较远时，调制和成丝一一对应，且满足局部能量守恒定律，与线性扰动理论的结论相一致；硬边光阑引起光束边缘开始出现调制，随后调制一直增长，最终光束分裂成丝。 2. 自由空间情形下，分析了发散光束的小尺度自聚焦调制谱增益特征，发现小的初始曲率半径可以延长成丝距离，说明发散光束可在一定程度上抑制小尺度自聚焦。进而推广到介质含有增益和损耗的情形，结果表明在输入功率、传播距离相同时，小尺度调制的最大增长频率和最大增益随着介质增益的增大而增大；在输入功率、介质增益相同时，随着传输距离的增大，小尺度调制的最大增益一直增大，最大增长频率在R>2/的情况下一直增大, 而对于R<2/的情况，最大增长频率在一定的传输距离内有一个先减小后增大的演变过程。在输出功率相同的情况下，小尺度调制的最大增长频率及最大增益随着介质小信号增益的增大而减小，说明对于发散光束来说小输入高增益能够在一定程度上抑制小尺度自聚焦。在损耗介质情形下，一定的传输距离内，随着介质损耗的增加，小尺度调制的最大增长频率和最大增益也随之减小，给定介质损耗的条件下，随着传输距离的增大，小尺度调制的最大增益增大，而最大增长频率却减小。 3. 分析了光束的发散性对空间滤波器滤波的影响，结果表明想要滤掉增长最快的频率成分，要适当控制发散波面曲率半径的大小，曲率半径的选择需要使入射光束的调制边频项和背景光场的频率产生一定的分离。 4. 提出将光楔列阵和光谱色散匀滑技术相结合以改善靶面辐照均匀性，进行了可行性探索研究，模拟计算结果表明，通过光楔列阵可以在靶面获得边缘陡峭且没有旁瓣的焦斑，不同子光束之间干涉所引起的细密条纹可以利用SSD技术消除，若对光楔列阵各光楔边缘进行软化，匀滑效果效果可更佳。 本论文的主要工作虽是在理论方面的探索，但对实际工作有一定的参考价值，有助于指导我们更加优化的设计高功率驱动器。 |
| 英文摘要 | The high-power laser drive device need much high pulse power, good beam quality and have a harsh demand for the uniform on-target irradiation.So how to promote laser power and improve the uniformity has long been important research topics.Small-scale self-focusing caused by nolinear refractive index, is one of the main factors that limit high power laser system’s output power and worsen the beam quality. So research on the propagation rules of small-scale self-focusing and the method to suppress it is the key to impove the output power.The divergent beam having divergent wave surface is helpful to suppress the small-scale self-focusing..In addition, Considering the influence of the small-scale self-focusing on the beam quality,it is needful find smoothing technique with large tolerance level of beam intensity and phase distortion.In order to obtain good smoothing effects,in practical application the combination of the smoothing techniques spatially and the smoothing techniques temporally is the effective method. In this dissertation, focusing on the small-scale self-focusing and the uniform on-target irradiation, we have carried out the theoretical research in the following respects: 1. We numerically simulate the propagation in the nonlinear material with two different initial conditions, employing the split step fourier method. The results show that the small-scale modulation grow exponentially, when the modulations are apart far from each other, the filament is one-to-one correspondent to the modulation and it satisfies the local energy conservation law. Owing to hard-edge aperture the modulations appear first at the beam margin, and then grow all long, finally the beam splits into multiple filaments. 2. In the free-space condition, we analysis small-scale modulation features of the divergent beam .we find that small initial radius extends the distance at which the filaments are formed .So it is indicated that small-scale self-focusing can be suppressed by divergent beam to a certain extent.Furthermore, the Bespalov Talanov theory is extended to the divergent beam in medium with gain and loss. The results show that in the case of the small signal gain, for a given input power and the propagation distance, the largest growing frequency and the maximum growth of small-scale modulation both increase with the increase of medium gain. for a given input power and medium gain,the the maximum growth of small-scale modulation increase following the increase of the propagation distance, while the largest frequency is always increasing when R>2/,and when R<2/ the largest frequency increases at first then decreases in certain propagation distance. For a given output power, the increase of the medium gain can make the maximum perturbation growth and largest growing frequency decrease. It is indicated that small input and high medium gain are helpful for suppressing the small-scale self-focusing.In the case of the medium loss, it is shown that the larger the medium loss, the smaller the fastest growing frequency and the maximum gain of perturbation with defined propagation distance. For given medium loss the maximum gain of perturbation becomes larger, while the fastest growing frequency becomes smaller as propagation distance becomes longer. 3. We analysis effects of the beam divergence on the filtering properties in spatial filters, the result shows that curvature radius should be accessed carefully to gain certain smoothing. If we want to filter the fastest growing frequency in small-scale self-focusing, we must control R to a proper value to make the spectrum separate. 4. We propose a scheme for improving irradiation uniformity by combing a segmented wedge array and spectral dispersion is presented. Detailed simulation shows that a quasi-near-field pattern without side-lobes can be achieved in that interference stripes inside the pattern from a segmented array can be smoothed out by the spectral dispersion.further more,if the edge-softed wedge array is used ,the better smoothing can be obtained. Although the work in this thesis is performed in theory, it is helpful to optimally design high-power laser drive device. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15605]  |
| 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 | 张艳丽. 高功率激光小尺度自聚焦和光束匀滑技术研究[D]. 中国科学院上海光学精密机械研究所. 2009. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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