飞秒激光成丝诱导远程击穿光谱技术
文献类型：学位论文
| 作者 | 郭豪 |
| 文献子类 | 硕士 |
| 导师 | 王铁军 |
| 关键词 | 飞秒激光成丝 Filamentation 激光诱导击穿光谱技术 Laser Induced Breakdown Spectroscopy 远程探测 Remote Detection 偏振光谱 Polarization-Gated Spectroscopy 自吸收效应 Self-Absorption Effect |
| 其他题名 | Filament Induced Remote Breakdown Spectroscopy |
| 英文摘要 | 飞秒激光在空气中传输时会受到克尔自聚焦效应及等离子体散焦效应的作用，在空气中形成很长的稳定的等离子体通道，此即飞秒激光成丝现象。由于光强钳制效应，光丝内部的激光功率密度在很长的空间范围内近似不变，可以很好地降低光强浮动、样品表面不平整等因素的干扰，结合飞秒光丝可以远程产生和操控的特性，飞秒激光成丝技术在远程探测方面有很大的优势，被广泛应用在金属、生物材料、气溶胶等各种形态样品的远程探测。 本文首先简要介绍了飞秒激光成丝远程探测、激光诱导击穿光谱偏振特性以及自吸收效应研究进展，随后介绍了飞秒激光成丝过程中的非线性效应，以及飞秒激光诱导等离子体的特性，然后以飞秒激光成丝诱导远程击穿光谱技术为核心，详细介绍了飞秒激光成丝诱导远程击穿光谱偏振技术、飞秒激光成丝远程诱导有机物荧光光谱以及飞秒激光成丝诱导等离子体自吸收效应等工作内容，主要的创新性研究内容和成果总结为： 1.飞秒激光成丝诱导远程击穿偏振光谱技术。在传统的远程探测系统收集装置前加入了激光偏振选择器件--偏振片，利用空气中飞秒激光与物质相互作用产生的连续背景与原子荧光谱线具有不同偏振特性的原理，通过旋转偏振片的偏振透过角度，抑制荧光光谱中的连续背景。实验结果表明当偏振片置于垂直于入射激光线偏振方向时，连续背景被抑制了42%，大幅度提高了光谱信背比。通过分析飞秒激光成丝诱导远程击穿光谱连续背景的偏振特性，提出了飞秒激光非线性效应产生的超连续白光是连续背景的主要来源。 2.飞秒激光成丝远程诱导有机物荧光光谱。我们搭建了飞秒激光成丝远程诱导有机物荧光实验系统，先在2.5米远处对光丝远程诱导有机物荧光进行了原理上的研究，通过安托因方程以及理想气体状态方程计算了醇类挥发物的浓度，并完成了荧光光谱的浓度校正，随着不同醇类挥发气体含碳原子数的增加，C-H、C-N等谱带强度也随着增加，通过提取浓度校正后C-H、C-N谱带强度的强度，可以完成醇类间的鉴别。我们还研究了不同样品C-N谱带与C-H谱带强度比值与气体浓度的关系，其比值在不同浓度下基本维持在一个固定值，也可用于远程醇类间的鉴别。在之前实验的基础上，对远程探测系统进行了升级，成功在9.95米远处探测到了醇类C-H 431nm荧光信号，随后我们根据R.M. Measure提出的雷达方程，对探测距离进行了等效性外推，在相同实验条件下，最远可以在82米处探测到荧光信号，若改进实验条件，通过该技术在10千米远处检测到醇类挥发气体是可行的。 3.飞秒激光成丝诱导等离子体自吸收效应研究。在飞秒激光成丝诱导远程击穿铝片实验中，我们观察到了Al原子谱线存在明显的自吸收现象。我们初步研究了能量和啁啾对飞秒激光成丝诱导远程击穿Al光谱的自吸收效应的影响。研究发现随着入射激光能量的增加，Al原子谱线中心位置处 (394.920 nm和396.668 nm)逐渐内陷，谱线呈现自反转结构。随后我们研究了啁啾对自反转结构的影响，发现当入射激光加有负啁啾时，飞秒激光成丝诱导远程击穿Al光谱的整体强度明显降低，谱线自吸收结构也有所减弱。; During its propagation in air, an intense femtosecond laser pulse experiences Kerr self-focusing and plasma defocusing resulting in the formation of self-guided plasma channels, named filaments. Because of intensity clamping, the influence of the variations of laser intensity and sample surface on laser induced plasma spectra are minimized. Therefore filament induced breakdown spectroscopy is widely used in remote sensing of metals, biological materials, aerosols and so on. In this thesis, beginning with a brief introduction on filament induced remote breakdown spectroscopy, polarization-resolved laser-induced breakdown spectroscopy, and self-absorption effect, then we present our recent works on polarization-gated filament induced remote breakdown spectroscopy, filament induced organism fluorescence spectroscopy and self-absorption effect in filament induced remote breakdown spectroscopy. Our recent results are briefly summarized as: 1.Polarization-Gated Filament Induced Breakdown Spectroscopy. By inserting a polarizer before the detector, the continuum background was reduced by more than 42% in filament-induced breakdown spectroscopy at a distance of 3.8 m, while the fluorescence intensity of aluminum atomic lines remained constant. We demonstrated a simple technique to filter out the continuum background in filament-induced remote breakdown spectroscopy. Supercontinuum through self-phase modulation during filamentation mainly contributes to the continuum background. The polarization-gated technique provides a simple way to remove the continuum background in filament-induced remote breakdown spectroscopy. 2.Remote Filament Induced Organism Fluorescence Spectroscopy. A principal setup on remote filament induced organism experimental system was established at a working distance of 2.5m. First, we investigated the underlying mechanism of filament remote induced fluorescence spectra, then Antoine function and Ideal Gas Law were used to determine the density of volatile gases. The results show that the intensity of C-H and C-N band fluorescence is proportional to the C numbers in the molecules which can be used to distinguish the alcohols with different C-number from each other. Then the relationship between the fluorescence intensities of C-H and C-N bands and the gas densities were investigated. The spectral data show that the ratio of C-N/C-H band was nearly constant under different gas density, which can also be used to distinguish the alcohols. Then by upgrading filament remote induced fluorescence experimental system, we successfully obtained the fluorescence signals from volatile gases at a distance of 9.95m. By using LIDAR function to determine the extrapolated distance of our system, the typical fluorescence could be detected at the distance of 82 meters. This technique for sensing the alcohol gases can work at a remote distance up to 10 km if certain upgrade is made. 3.Self-Absorption Effect in Filament Induced Remote Breakdown Spectroscopy. Strong self-absorption effects as well as self-reversal structures were observed at filament induced remote breakdown experiments. The effects of energy and chirp of incident laser on self-reversal structure were investigated. The results demonstrated that, with the increase of energy of incident laser, the center of the atomic lines of Al became reversal. The intensities as well as self-reversal structures of the spectra were minimized when the incident laser was negatively chirped initially. |
| 学科主题 | 光学工程 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/31064]  |
| 专题 | 中国科学院上海光学精密机械研究所 |
| 作者单位 | 中国科学院上海光学精密机械研究所 |
| 推荐引用方式 GB/T 7714 | 郭豪. 飞秒激光成丝诱导远程击穿光谱技术[D]. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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