| 题名 | 冷原子物理用光纤激光技术研究 |
| 作者 | 胡金萌 |
| 学位类别 | 博士 |
| 答辩日期 | 2015 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 冯衍 |
| 关键词 | 掺镱光纤激光 拉曼光纤激光 波长调谐 自发辐射放大 冷原子物理 |
| 其他题名 | Study on fiber lasers for cold atom physics |
| 中文摘要 | 冷原子物理、激光光谱学作为基础研究领域，不仅加深了人类对物质本质和基础自然规律的理解，其研究发展过程中衍生的频标、光梳、质谱仪等技术在学术界、工业界均有广泛应用，具有重要的研究意义。冷原子物理、激光光谱学的进一步发展离不开实验条件的持续完善，激光作为实验装置的重要部分，在实验研究和成果应用中有着举足轻重的作用。这些领域所需的激光需与实验元素的能级、跃迁对应，波长特殊而较难获得，一定程度上阻碍了冷原子物理等领域的进一步发展。光纤激光器自问世以来，以其相对传统激光器在效率、体积、结构、散热、光束质量等方面的优势，一直倍受关注。随着大模场双包层光纤和高功率半导体激光泵浦源的技术进步，近年来光纤激光飞速发展，广泛应用于工业加工、国防、医疗、科研等领域。目前基于稀土元素掺杂光纤和光纤非线性效应的光纤激光已可实现1-2μm宽广波段的较高功率输出，辅以倍频、和频的频率转换技术，可实现各种特殊波长的激光输出，在冷原子物理、激光光谱学等领域有着广阔的应用前景。本文深入研究了光纤激光器的光谱调节技术，针对几个具体应用，采用掺镱光纤激光技术、拉曼光纤激光技术研制了相应的特殊波长激光器，并对其有效性与实用性进行了验证，探索了光纤激光在冷原子物理、激光光谱学等领域的应用前景。主要研究内容如下： 1. 针对汞原子激光冷却必需的253.7nm紫外激光这一具体应用，作者研制了室温下1014.8nm单频掺镱光纤放大器以通过四倍频获得该紫外激光，与传统的1014.8nm固体激光器、半导体激光器或液氮制冷的掺镱光纤放大器相比，提高了输出激光功率、简化了实验装置。研究过程中以理论分析、数值模拟和实验验证三方面探索了掺镱光纤中自发辐射放大（ASE）的控制方式，单级掺镱光纤放大器获得了8.06W的最终输出，斜率效率21.9%，直接输出中ASE峰值低于信号光25.4dB，在国际上首次实现1014.8nm室温下使用掺镱光纤的单频放大。通过两级掺镱光纤放大器获得的19.3W激光，是目前掺镱光纤激光器在短波段（<1020nm）最高的单频输出功率，进一步的功率提升则需使用受激布里渊散射抑制技术。在此基础上，采用商业倍频器完成了4W 1014.8nm激光的外腔谐振倍频与四倍频，获得了75mW的253.7nm紫外激光，并由此测得了汞原子1S0 – 3P1跃迁的吸收谱与饱和吸收谱，验证了系统的有效性和实用性。 2. 研究了1-1.1μm宽调谐掺镱全光纤激光器/放大器，以自制的1000-1099nm宽调谐掺镱光纤环形振荡器为基础，实验探索了掺镱光纤放大器在1-1.1μm波段的性能，重点研究了掺镱光纤放大器在1020nm以短波长的表现。经过两级放大，可提供1014-1080nm范围内>30W的激光输出，是目前宽调谐掺镱全光纤激光器中调谐范围最宽、工作波长最短的报道。通过数值计算分析了短波段掺镱光纤放大器中种子光信噪比的影响，增益光纤长度的优化和理想情况下单级放大器最高增益，为放大器的进一步优化提供了理论指导。该研究不仅为1-1.1μm波段单频掺镱光纤放大器打下了坚实的基础，在掺镱固体的激光制冷领域也有重要应用。 3. 拉曼光纤激光器作为一种重要的光纤激光器类型，对其在冷原子物理、激光光谱学领域的应用进行了探索。针对4He元素23P‐31,3D跃迁的荧光光谱实验，研制了1176nm单频拉曼光纤放大器及配套的1120 nm掺镱光纤振荡器，以光纤轴向应力梯度的方式较好地抑制了其中的SBS效应，由63.5W的1120nm泵浦激光获得了8.5W的1176nm拉曼激光，转化效率约13.4%。使用商业化的周期极化晶体单通倍频器进行了1178.3nm倍频的验证性实验，获得的589nm激光可用于钠原子的激光冷却等实验。 |
| 英文摘要 | Cold atom physics and laser spectroscopy, have been shedding lights on the fundamental physics laws and the very nature of matter. Technologies such as frequency standards, frequency combs, mass spectrometer come from the study of these areas and are widely used in industry and scientific research, further study in such basic research fields are of great value. Laser, an essential tool for the experiment, plays an important role in development of cold atom physics and laser spectroscopy. Laser required in such areas needs to match the energy levels and transitions of the elements studied, its wavelength often is quite unique and difficult to obtain, which hinders the further development of these areas. Fiber lasers have drawn lots of attentions, because of its higher efficiency, smaller size, easier thermal management and better beam quality compared with traditional lasers. As the development of the large mode area double clad fiber and high power diode pump lasers, fiber lasers have been growing rapidly in recent years, and found wide applications in areas like industry, national defense, medical treatment, scientific research and etc.. Nowadays, rare-earth doped fiber lasers and nonlinear fiber lasers have fulfilled high power output over the wide wavelength range of 1-2 μm. With frequency conversion techniques, most specific wavelength can be realized by fiber lasers, hence the great potential of fiber lasers in research fields such as cold atom physics and laser spectroscopy. In this paper, we focus on a few of specific research in laser cooling and laser spectroscopy, developed and tested such fiber lasers of specific wavelength, investigating the potential of applying fiber lasers in these areas. Details are as follow: 1. 253.7 nm UV laser is required by laser cooling of mercury atoms. To generated this UV laser by frequency quadrupling, we developed 1014.8nm single frequency Yb-doped fiber amplifier working under room temperature. Compared with the solid state laser, diode laser and liquid-nitrogen cooled Yb-doped fiber laser used, our laser provides much higher power with simpler structure. The controlling of amplified spontaneous emission (ASE) in Yb-doped fiber is investigated by means of theoretical analysis, numerical simulation and experiments, 8.06 W 1014.8 nm laser is obtained by single stage amplification with a sloped efficiency of 21.9%, and ASE 25.4 dB lower than the signal. To our knowledge, this is the first time to amplify 1014.8 nm laser with Yb-doped fiber under room temperature. 19.3 W laser power was achieved with boost amplifier, limited by stimulated Briullion scattering (SBS), which is the highest power reported for a single-frequency Yb-doped fiber laser at this wavelength region. 4 W 1014.8 nm laser is then frequency quadrupled to 253.7 nm by two sets of commercial frequency doublers, and 75 mW ultraviolet laser is obtained. With this UV radiation, both transmission and saturated absorption spectra of the 1S0 – 3P1 transition of atomic mercury are measured, proving that this Yb-doped fiber amplifier is applicable for mercury cooling. 2. 1-1.1 μm tunable Yb-doped all-fiber lasers and amplifiers is studied. With the wavelength tunable Yb-doped fiber ring oscillator over 1000-1099 nm we built, the performance of Yb-doped fiber amplifiers over the range of 1-1.1 μm is investigated, especially when the wavelength is shorter than 1020 nm. By two-stage amplification, >30 W laser is achieved over the wavelength range of 1014-1080 nm. To our knowledge, this is the widest tuning range and shortest working wavelength for an Yb-doped all-fiber laser so far. The influence of seed’s signal to noise ratio，the optimization of gain fiber length over signal wavelength, and the theoretical gain limit by ASE and parasitic oscillation of Yb-doped fiber amplifiers over the short wavelength range (<1020 nm) is also numerical analyzed based on the physical model of Yb-doped fiber amplifiers, as instructions for the amplifiers’ further optimization. Not only this research lays the foundation of single frequency Yb-doped amplifier over the range of 1-1.1 μm, but also this widely tunable laser is of great use in laser cooling of Yb-doped solids. 3. As an important kind of fiber lasers, the applications of Raman fiber lasers in cold atom physics and laser spectroscopy were also investigated. For the fluorescence spectroscopy study of the 23P‐31,3D transitions in 4He, we developed a set of 1176 nm single frequency Raman amplifier and its pump laser 1120 nm Yb-doped fiber oscillator. By adopting longitudinally applied strain distribution onto the Raman gain fiber to suppress the SBS effect, 8.5 W 1176 nm laser are achieved with 63.5 W 1120 nm laser with efficiency of ~13.4%. Frequency doubling experiment is also performed at 1178.3 nm to test the Raman laser, with commercial frequency converter based on periodical poled crystal, its second harmonic 589 nm can be used in laser cooling of sodium atoms. |
| 语种 | 中文 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15913]  |
| 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 | 胡金萌. 冷原子物理用光纤激光技术研究[D]. 中国科学院上海光学精密机械研究所. 2015. |
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