| 题名 | 空心锥引导和聚焦激光传输特性的研究 |
| 作者 | 曾夏辉 |
| 学位类别 | 博士 |
| 答辩日期 | 2010 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 范滇元 |
| 关键词 | 空心锥，传输特性，光学引导，聚焦，透射增强效应 |
| 其他题名 | Research on Transmission Characteristics of Guiding and Focusing Laser Light Using an Open Hollow Cone |
| 中文摘要 | 超短超强激光技术的持续发展推动了高能量密度物理这一前沿研究领域的蓬勃发展，特别是强激光加速高能电子、质子，激发X射线，快点火激光聚变等，更是当前国际上十分活跃的研究方向。这些研究都涉及激光与等离子体的相互作用。如何有效地聚焦并导引激光注入等离子体就成为首先要研究并回答的一个重要问题。自2001年利用空心锥靶成功进行了快点火演示试验以来，空心锥结构就成为常用的导引和聚焦方式。另一方面，在近场扫描光学显微研究领域中，实现亚波长空间分辨能力的关键构件也正是亚波长尺度的锥形探针。因此，对空心锥引导和聚焦激光的传输特性进行深入细致的研究分析，是必要而有实际意义的。 学位论文针对典型的空心锥结构，运用时谐电磁场和波导模式理论，导出了空心锥波导中传输模式的解析表达式，系统地分析了电磁场模式的场型结构和空间分布、传播常数（衰减系数和相位常数）、波阻抗等主要的传输特性；运用时域有限差分(FDTD)数值方法，研究了不同光波波长、不同入射方式（单光束正入射、多光束斜入射）情况下，空心锥引导和聚焦激光的物理机制和传输特性；进而研究了空心锥引导和聚焦激光的能力与锥几何结构的依赖关系，提出了空心锥结构优化设计的准则和实例；对具有亚波长尺度的空心锥，导出了波导模式的解析表达式，探讨了透射特性及锥内表面刻蚀的透射增强效应。创新性研究成果在Optical Express、Optics Communication 等国内外学术刊物发表（SCI五篇，EI一篇），申请发明专利两项。 论文的主要内容如下： (1) 首次利用时谐电磁场和波导模式理论推导了空心锥波导中传输模式的解析表达式。运用数值求解获得的精确本征值，系统地分析了电磁场模式的场型结构和空间分布、传播常数（衰减系数和相位常数）、波阻抗等主要的传输特性。结果表明空心锥内存在的传输模的场型结构与圆柱型波导内存在的传输模的场型结构相似，但他们的传输特性以及能量密度分布却有很大的区别。锥内传输模式与倏逝模式之间的转变不是一个突变过程，而是一个缓变过程。各模式的衰减系数随着 值的减小而增大，而相位常数从 变化到零，能量密度随着径向半径的减小而不断增大，越靠近出射端口，其能量越趋于集中。此外，各传输模在空心锥中传播时不存在确定的截止波长，而是存在一截止半径，截止半径的大小与电磁波波长和空心锥的锥角有关。 (2) 利用FDTD方法首次从数值上验证了空心锥确实能光学引导和聚焦激光。空心锥引导和聚焦激光的效果随着倾斜入射角的增大而变得越来越差。然而，当多束对称倾斜的激光同时入射到空心锥中时，空心锥引导和聚焦激光的能力会得到提高。空心锥引导和聚焦激光的能力与光波波长有很大的联系。数值结果显示通过合理设计空心锥结构可使得每一个波长的激光都能被空心锥引导和聚焦。 (3) 探讨了空心锥引导和聚焦激光的能力与锥几何结构的依赖关系，为表征这种依赖关系引入了锥角和锥尖出射孔径两个重要的结构参量。通过改变这两个结构参量可以获得对激光聚焦强度、锥尖出射孔径外光场的空间分布以及近场透射系数等传输特性的控制。在理解上述物理机制的基础上提出了空心锥结构优化设计的准则和实例。 (4)推导了亚波长空心锥内球横电模和球横磁模各电磁场分量的解析表达，探讨了透射特性及锥内表面刻蚀的透射增强效应。运用数值求解获得的精确本征值，详细地分析了亚波长空心锥内时间平均能量密度分布与各存在的模式、光波波长、锥的长度、输出孔径尺寸以及锥角之间的关系。锥角越大或光波波长越小，锥内时间平均能量密度的空间分布振荡周期越小，出现最大值的位置越靠近锥出射端口小孔。而输出孔径的大小不影响时间平均能量密度在锥内呈准周期性的振荡分布，但影响最大值与出射小孔间的距离。空心锥的长度对亚波长空心锥内时间平均能量密度呈准周期性振荡分布的影响很小，但能量密度的强度会随空心锥长度的增大而减小，从而减小在出射小孔处的光透射。研究还发现激发出来的表面等离子体激元波可以提高亚波长空心锥的透射率，也能够促使光学仪器的空间分辨率得到大大的提高。在亚波长空心锥内刻蚀可以更好地激发和引导表面等离子体激元波到达出射孔径端口，从而提高亚波长空心锥的透射率和增强光学仪器的空间分辨率。 |
| 英文摘要 | The sustainable development of ultra-short ultra-intense laser technology has facilitated enormous progress in frontier studies of high energy density physics. Especially, the intense laser accelerated energetic electrons and protons, the generation of X-ray and fast ignition research in inertial fusion are hot topics, which involve the interaction of laser with plasmas. Among these hot topics, it is an important question to answer that how laser light are guided efficiently to inject into plasmas. Since the experiment on small-scale fast ignition was performed using hollow cone target in 2001, the geometry structure of hollow cone has been a popular method of guiding and focusing laser. On the other hand, the key component of the scanning near-field optical microscope systems is just a conical probe with a sub-wavelength-sized exit hole that determines the basis for the scanning near-field optical microscope systems achieving sub-wavelength spatial resolution. Therefore, it is very necessary to carry on through going and painstaking studying to the transmission characteristics of guiding and focusing laser light using an open hollow cone, which has practical significance and value to optimizing the interaction of laser with plasmas and enhancing spatial resolution and transmission efficient for the scanning near-field optical microscope systems. In the present thesis, aiming at a typical geometry structure of open hollow cone, the explicit analytical expressions of propagating modes inside the hollow cone based on the time-harmonic electromagnetic field and waveguide mode theory. And the main transmission characteristics including the electromagnetic fields configurations, the spatial distributions of electromagnetic field components, the wave impedance and the propagation constant such as attenuation and phase constants are analyzed systematically. The transmission characteristics and physical mechanism of the cone-guiding and focusing laser light under condition of different wavelength or incidence style (single-beam normal and muli-beam oblique incidence) are investigated by finite-difference time-domain (FDTD) method. Furthermore, the dependence of the cone geometry on the cone-guiding and focusing laser light is investigated, and the optimization design guidelines and practical examples are presented. In addition, the explicit analytical expressions of propagating modes inside an open hollow conical waveguide with a sub-wavelength-sized exit hole are derived, and the transmission properties and the extraordinary optical transmission due to parallel grooves etched in the core are investigated. Some innovative results have been presented in domestic and foreign academic journals including Optics Express and Optics Communication, and two achievements applied for patent. The main innovative results in our thesis are summarized as follows: (1) Based on the time-harmonic electromagnetic field and waveguide mode theory, explicit analytical expressions of propagating modes inside an open hollow cone are derived for the first time. Accurate eigenvalues obtained numerically are used to analyze the main transmission characteristics including the electromagnetic fields configurations, the spatial distributions of electromagnetic field components, the wave impedance and the propagation constant such as attenuation and phase constants. It is shown that the propagating modes configurations inside the hollow cone are similar to those in a cylindrical hollow waveguide, but the transmission characteristics and energy densities distributions along propagating direction have a different behavior. The mode conversion between all propagating and evanescent modes is not an abrupt change process, but a slow varying process. A strict distinction between pure propagating and pure evanescent modes can not be achieved. As decreases, the value of the attenuation constant increases, and the phase constant changes from ~-k to 0. The energy density is increasing constantly with decrease of radial radius. The closer it is to exit hole, the more concentrative the energy density is. There is no well-defined cutoff wavelength but rather a cutoff radius. It is interesting to note that the magnitude of the cutoff radius is related to the wavelength and the cone half-angle. (2) The fact that an open hollow cone can optically guide and focus laser light is verified by finite-difference time-domain simulations. As the oblique incident angle increases, the effect of cone-guiding and focusing laser light deteriorates gradually. However, the ability of cone-guiding and focusing laser light is enhanced when multiple beams with the symmetrical oblique angles incident on the hollow cone, and it dependes strongly on the wavelength of light. Simulation results show that laser light with any wavelength can be guided and focused by hollow cone with reasonable designed structure. (3) The dependence of the cone geometry on the cone-guiding and focusing laser light is investigated. Two important parameters, cone angle and cone tip size, which characterize the cone-focusing effect are introduced. It is show that by changing these parameters, the transmission characteristics including the laser intensification, field spatial distribution at the cone tip and the near-field transmission can be controlled. Based on these understandings on the above physical mechanism, the optimization design guidelines and practical examples are presented. (4) The analytical expressions for the field components of the spherical transverse-magnetic (TM) and transverse-electric (TE) modes inside an open hollow conical probe with a sub-wavelength-sized exit hole are derived, and the transmission properties and the extraordinary optical transmission due to parallel grooves etched in the core are investigated. By using the accurate eigenvalues obtained numerically, the influence of the wave mode, the light wavelength, the cone angle, the exit aperture diameter as well as the length of the conical probe on the time-averaged energy density distribution inside the sub-wavelength hollow conical probe are discussed in detail. The oscillation period of the time-averaged energy density spatial distribution decreases with the increases of the cone angle and the decreases of the light wavelength and the position of a clearly pronounced maximum for the time-averaged energy density is closer to the exit hole of the conical probe. Although the exit aperture diameter has not effect on the quasi-period oscillation of the time-averaged energy density spatial distribution, it has effect on the distance between the position of an appreciable maximum and the exit hole. In addition, the length of the conical probe has little effect on the quasi-period oscillation of the time-averaged energy density spatial distribution, but the intensity of energy density decreases with the increase of the length of probe, which will result in the decrease of optical transmission at exit hole. It is also shown that the excited surface plasma polariton (SPP) can enhance the transmission of the sub-wavelength probe and achieve the great improvement of spatial resolution of optical instrument. Corrugations inside the sub-wavelength probe can excite and guide the SPP wave to exit hole better, which resulting in enhancing transmission of the sub-wavelength probe and spatial resolution of optical instrument. |
| 语种 | 中文 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15631]  |
| 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 | 曾夏辉. 空心锥引导和聚焦激光传输特性的研究[D]. 中国科学院上海光学精密机械研究所. 2010. |
| 个性服务 |
| 查看访问统计 |
| 相关权益政策 |
| 暂无数据 |
| 收藏/分享 |
除非特别说明，本系统中所有内容都受版权保护，并保留所有权利。
修改评论