| 题名 | 远程钠层磁场探测技术研究 |
| 作者 | 范婷威 |
| 文献子类 | 博士 |
| 导师 | 冯衍 |
| 关键词 | 磁力计 Magnetometer 钠导星 Sodium laser guide star 拉莫尔进动 Larmor precession 地磁场 Geomagnetic field 钠原子 Sodium atom |
| 其他题名 | Research on remote sensing of geomagnetic field in the sodium layer |
| 英文摘要 | 远程钠层磁场探测技术是结合钠激光导星和光原子磁力计提出来的一项新技术，用于探测海拔85-110 km区域的磁场。传统磁场探测手段如Swarm星载磁传感器运行在450-500 km高度，而高空科学气球的飞行高度一般在40-50 km，故基于钠层的磁场探测可以弥补中间高度磁场测量技术的空白。中间高度磁场测量对于完善和校正全球地磁模型有重要意义。85-110 km区域的磁场可作为重要科学现象的观测窗口，比如外地幔特性，电离层的太阳能静发电机，离子电流（与反应气候变化的洋流运动有关）。此外，中间层处于电离层底部，测量电离层底部磁场变化是理解磁场和电离层之间关系的关键。钠层磁场探测可对电离层底部磁场进行连续的长期测量，可用于监测与极光相关的磁干扰，这对于有极光活动的地区特别重要。本文围绕远程钠层磁场探测技术，在钠激光导星亮度提升与磁场探测方法、实验室钠原子磁力计以及远程钠层磁场探测等方面展开理论和实验研究，主要研究内容包括： 1. 研究钠层磁场探测技术，需要深入理解在钠层的复杂环境下，激光与钠层相互作用的物理机理。采用Bloch方程进行数值模拟，详细介绍了拉莫尔频率脉冲光用于提升钠激光导星亮度，以及用于钠层磁场探测的数值模拟结果。探讨了限制钠激光导星亮度的因素，并提出偏振转换激光泵浦——使激光偏振以拉莫尔频率在左右旋圆偏振间转换，来提升钠激光导星的亮度。建立了偏振转换理论模型，以欧洲南方天文台位于帕瑞纳（Paranal）的激光导星系统为例，系统地研究了偏振转换过程中基态磁子能级的布居几率演化特征，及激光与地磁场夹角、再泵浦比例对钠导星亮度提升的影响，数值模拟结果显示，在激光与地磁场夹角为90?时，回波通量提升40%。分析了连续波钠激光导星亮度随左、右旋圆偏振转换频率的变化，在此基础上提出了偏振转换可以作为远程钠层磁场探测的一种方案。此外，进一步分析了连续波激光幅度调制结合偏振转换方案在提升钠导星亮度及测磁上的可行性。 2. 在实验室搭建了钠原子磁力计系统，验证了远程钠层磁场测量原理——对连续波激光进行幅度调制，扫描调制频率，利用钠荧光强度随调制频率的变化反演磁场。将激光波长调谐到Na D1或D2线，研究了钠原子荧光的磁共振随激光光强、脉冲占空比和磁场值的变化。使用单个幅度调制激光束，演示了基于充有缓冲气体He的钠蒸气池的磁力计，并且在优化的实验条件下：钠池温度为60?C，峰值激光强度为65 W/m2，脉冲占空比为17.5%，利用Na D1线实现了150 pT/Hz1/2的散粒噪声极限灵敏度。这项工作是实现中间层钠灵敏远程磁场测量的重要一步。 3. 进行了远程钠层磁场探测实验，包括在上海进行的钠层磁场探测尝试和摸索，以及在丽江高美古观测站所做的钠层磁场探测实验，为下一步实验积累了宝贵经验。分析了提升钠层磁场探测灵敏度和空间分辨率的手段。; Combining sodium laser guide star and optical magnetometry, remote sensing of geomagnetic fields in the sodium layer was proposed for remote measurement of geomagnetic field at an altitude of 85-110 km. Conventional magnetic sensors such as Swarm satellite-borne magnetic sensors operate at altitudes of 450-500 km, while high-altitude science balloons fly at 40-50 km. Laser remote magnetometry using mesospheric sodium fill the gap between space-based and near-Earth measurement, which is of great significance for perfecting and correcting the global geomagnetic model. Magnetic-field sensing at intermediate length scales, in the range of several tens to several hundreds of kilometers likewise offer a window into important scientific phenomena, including the behavior of the outer mantle, the solar quiet dynamo in the ionosphere, and ionic currents as probes of ocean circulation, a major actor in models of climate change. In addition, the mesosphere is at the bottom of the ionosphere. Measuring the magnetic variations at the bottom of the ionosphere is the key to understanding the relationship between the magnetic field and the ionosphere. Remote sensing of geomagnetic fields in the sodium layer allows for continuous long-term measurements of the magnetic field at the bottom of the ionosphere, providing a tool for monitoring magnetic disturbances in conjunction with the aurora, which is of particular interest in regions with auroral activity. This article focuses on remote sensing of geomagnetic fields in the sodium layer, and conducts theoretical and experimental research on sodium laser guide star brightness enhancement and magnetic field detection method, laboratory sodium atomic magnetometer and remote magnetometry using mesospheric sodium. The main research contents include: 1. To study remote sensing of geomagnetic fields in the sodium layer, it is necessary to understand the physical mechanism of the interaction between the laser and the sodium layer in depth. The numerical simulation is conducted using Bloch equation, this paper simulate laser pulsed at Larmor frequency be used to increase the brightness of sodium guide stars and the detect magnetic field in the sodium layer. The factors that limit the brightness of the sodium laser guide star were discussed. Switching the laser between left and right circular polarization at the Larmor frequency is proposed to enhance the brightness of the sodium laser guide star. A theoretical model of polarization switching was established. With ESO’s laser guide star system at Paranal as example, numerical simulation shows that the return flux is increased when the angle between geomagnetic field and laser beam is larger than 60°, as much as 40% at 90°. Occupation probabilities of the eight ground state’s magnetic sublevels were systematically studied. The angle between the laser and the geomagnetic field, and the effect of the pumping ratio on the brightness of the guide star is shown in the numerical simulation results. The dependence of return flux on the polarization switching frequency is calculated, and the return flux peaks at Larmor frequency as expected. Based on this, the polarization switching can be used as a remote magnetometry method. In addition, the feasibility of improving the brightness of sodium guide stars and remote magnetometry by cw laser amplitude modulation combined with polarization switching was further analyzed. 2. A sodium atomic magnetometer system was set up in the laboratory to verify the principle of remote sensing of geomagnetic fields in the sodium layer—modulate the amplitude of the cw laser, scanning the modulation frequency, fluorescence intensity varies with modulation frequency, the magnetic field is inferred from the variation of fluorescence. With a 589 nm laser tuned at the D1 or D2 line, magnetic resonance of sodium fluorescence is studied with varying laser intensity, duty cycle, and field strength. A magnetometer based on a sodium vapor cell filled with He buffer gas is demonstrated, using a single amplitude-modulated laser beam. When the peak laser intensity is 65 W/m2, pulse duty cycle is 17.5%, and cell temperature is 60°C, a magnetic field sensitivity of 150 pT/ is achieved at the D1 line. The work is an important step toward sensitive remote magnetometry with mesospheric sodium. 3. Remote magnetometry with mesospheric sodium is conducted, including the exploration of the remote magnetometry in Shanghai, and the remote magnetometry experiment at the Gaomeigu Observatory in Lijiang, This experiment has accumulated valuable experience in remote magnetometry with mesospheric sodium for further improvement and refinement. Finally ways to improve the photon shot noise sensitivity and spatial resolution was analyzed. |
| 学科主题 | 光学工程 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/31034]  |
| 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 | 范婷威. 远程钠层磁场探测技术研究[D]. |
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