| 题名 | 高光束质量宽带OPCPA关键技术研究 |
| 作者 | 刘笑迪 |
| 文献子类 | 博士 |
| 导师 | 梁晓燕 |
| 关键词 | 光参量啁啾脉冲放大 Optical parametric chirped pulse amplification 非线性晶体 nonlinear crystal 光束质量 beam quality 调制度 modulaiton |
| 其他题名 | Research on some key technologies about broadband OPCPA with high beam quality |
| 英文摘要 | 超短超强激光为强场激光物理研究创造了极端的实验条件，在光与物质相互、粒子加速、阿秒脉冲等诸多研究领域起到了不可替代的推进作用，具有重要的应用价值和发展潜力。作为实现超短超强激光的主要技术方案，光参量啁啾脉冲放大(OPCPA)技术具有许多优良的特性，如高增益、宽带宽、高对比度、低热畸变等，对于激光系统的小型化以及高能量、超宽带、高重频输出的实现大有裨益。随着研究的不断深入，作为决定OPCPA高能激光系统输出性能的关键参数之一，光束质量对系统最终输出能力和实验应用、器件安全等起到至关重要的决定性作用。本论文针对OPCPA超短超强激光系统的这一关键问题，对宽带OPCPA输出性能开展研究，在考虑相位匹配、能量和转换效率的基础上，重点针对OPCPA放大过程中输出空间光束质量问题进行了详细分析，并探讨优化方法，主要研究成果如下： 1. 设计和搭建了一套小型化纳秒量级OPCPA实验平台，包括Nd：YLF泵浦源和钛宝石宽带信号源两大部分，为后续实验提供了可靠保障。其中，泵浦源基于Nd：YLF多级放大器，并结合主动的时间整形和严格的光传输系统，实现了重频2 Hz、脉宽2.3 ns、单脉冲能量约400 mJ、功率密度大于1 GW/cm2、超高斯型时空特性的输出指标；信号源是由飞秒振荡器、展宽器和钛宝石再生放大器组成的CPA系统，输出脉宽1.6 ns、光谱760—840 nm、毫焦耳量级的基模高斯脉冲。 2. 基于液晶空间光调制器、CCD等元件，配合自主开发的光束监测整形程序，实现了对纳秒级激光脉冲的高效率、操控灵活的主动型空间整形。相较于常规的被动整形，该主动整形方案无论是在整形效果，还是在实时可控性方面都有了很大提升。该方案是对激光空间性能实时监控和优化补偿的有效尝试，对开展高光束质量OPCPA实验创造条件。 3. 通过几种典型的OPCPA相位匹配结构分析OPCPA输出光束质量演变特性，研究不仅证明了几何结构对增益特性和光束质量的重要影响，还进一步验证了影响光斑和波前畸变的主要因素。其中，输出光斑主要与泵浦光和信号光重合度有关，减小泵浦光和信号光的偏离有助于优化输出光斑的均匀性和对称性，减小输出调制度；波前演化与光波间的偏离密切相关，泵浦光波前畸变严重时，泵浦与闲频光共线可以减小泵浦波前畸变向信号光的传递，泵浦光为近平面波时，信号光和闲频光重合有助于信号光波前的保持。实际OPCPA系统的设计应结合关键输出指标要求，选择合适的匹配方式，以更好的满足应用需求。以上结果发表在Optics Letters 41, 5809-5812 (2016)。 4. 对高效宽带OPCPA系统的输出空间特性进行了详细分析，研究发现OPCPA输出光束质量与注入调制度、放大程度和非共线及走离效应密切相关。对于注入调制度，注入泵浦光调制度起到决定性的影响作用，信号光调制度的影响相对较小且易于补偿。放大程度通过不同泵浦功率密度体现，选择合适的泵浦功率密度对与转换效率和输出调制度的协调优化至关重要。非共线和走离效应的影响在小光斑口径下愈加明显，导致严重的光斑畸变和转换效率的下降。我们发现采用特定的泵浦调制度类型可以有效补偿非共线结构和走离效应的不利影响，能大大减小输出调制度，同时增大转换效率和输出稳定性。以上结果发表于Optics Communications 383, 197-207 (2017)。 5. 理论和实验研究新型非线性晶体KBOB的宽带OPCPA特性。基于前述OPCPA实验平台，结合KBOB晶体特性，在I类相位匹配：(θ, φ) = (37.31°, φ = 90°)、非共线角α = 2.19°，实现了0.25 mJ到24 mJ的宽带放大，证明了KBOB在800 nm波段的宽带放大能力。该研究为近红外OPCPA提供了新的可选晶体和实施方案。随着晶体生长工艺的不断提升，它有望成为超短超强OPCPA激光系统的可靠增益介质。以上结果发表于 Laser Physics Letters 14, 095403, (2017)。; Ultra-fast, ultra-intense laser, which has provided extreme experimental conditions for high field laser physics, offers an irreplaceable strong boost in many reaearch fields such as light-matter interaction, electron acceleration, etc. As one of the main technical proposals for achieving ultra-short, ultra-intense laser, OPCPA has numerious excellent properties such as high gain, broad gain bandwidth, high contrast, little thermal distortion and so on, which benefit the realization of systemic miniaturization and high energy, broadband, high repetition-rate output. As the research going, optical quality, one of the key parameters that dominates the output performance of high energy OPCPA system, plays a vital and critical role in final output capacity, experimental application and device safety, etc. Considering that key issue of OPCPA ultra-short & intense system, this dissertation focused on the output property of broadband OPCPA, in addition to pahse matching, energy and converison efficiency, spatial beam quality of OPCPA process was analyzed in detail, optimization schemes were discussed as well. The main works are as follows. 1. We designed and built a compact ns-scale OPCPA experimental system, which include a Nd: YLF pump source and a Ti sapphire broadband signal source, to support the conduction of relevant experiments. Based on Nd: YLF amplifires and combined with temporal and spatial beam shaping and strict imaging relaying, the pump laser outputted 2 Hz, 2.3 ns, pulse energy up to 400 mJ, intensity higher than 1 GW/cm2 super-Gaussian pulses; The signal source, which was a Ti: sapphire CPA system composed of a femtosecond oscallitor, a stretcher, a broadband regenerative amplifier, and a compressor, outputted 1.6 ns, mJ-level Gaussian pulse with a spectral range of 760-840 nm, 2. Using spatial light modulator, CCD and other optical elements, together with a self-developed beam monitoring and shaping control program, a highly efficient and maneuverable active beam shaping for ns laser was achieved. Compared with trational negative shaping methods, our active approach not noly showed better shaping result, but also promoted the flecibility and controllability of laser systems, providing good condition for high beam quality OPCPA experimental reaserch. 3. The evolution of OPCPA output properties was analyzed in detail with several typically designed phase-matching geometries, the results not only confirmed the vital influence of phase matching on energeic gain and beam quality, but also made further verification about the main factors that affected beam and wavefront aberration. The output beam was closely related to pump and signal overlap, reducing their divergency contributes to better output beam uniformity and symmetry; wave separation affected amplified wavefron. Specially, for a strongly abberated pump wavefront, the homodromous pump and idler could reduce wavefront aberration transmission from pump to signal; for a plane pump, coincidece of signal and idler contributed to signal wavefront retaining. Thus, designing OPCPA scheme should combine demands on the key output index, and a proper phase matching geometry could be chosen to better meet application requirements. The above results were published on Optics Letters 41, 5809-5812 (2016). 4. Detailed analysis about the spatial beam quality of efficient broadband OPCPA amplifiers were made, it was found that OPCPA output beam quality was closely related to input modulation, amplification degree, and walk-off effect. Within the input modulation, input pump modulation was a dominant factor, signal influence was minor and relatively easy to compensate. Pump intensity was used to embody the amplification degree, selecting a proper pump intensity was crutial for concordant optimization of conversion efficiency and output modulation. The influence of non-collinear and walk-off effect was increasingly noticeable at small beam sizes, leading to spatial aberration such as beam asymmetry and decreased conversion efficiency. Thus, in addition to choosing proper pump intensity, a special pump modulation type was found to effectively compensate the above negative effects, conducing to low modulation and maximum conversion efficiency with high stability simultaneously. The above results were published on Optics Communications 383, 197-207 (2017). 5. The broadband OPCPA property of a noval nonlinear crystal KBOB was analyzed theorically and experimentally. Based on the OPCPA laser system, considering the feature of KBOB, broadband amplification from 0.25 mJ to 24 mJ was achieved using type-I phase matching with (θ, φ) = (37.31°, 90°) and noncollinear angle of α = 2.19°, confirming the broadband amplification ability of KBOB at near 800 nm wavelengths. This work provides new crystal and implementation for near-infrared broadband OPCPA. With the promotion of crystal growing process, it can be relable gain medium for ultra fast, ultra-high-intensity laser systems. The above results were published on Laser Physics Letters 14, 095403, (2017). |
| 学科主题 | 光学 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/31129]  |
| 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 | 刘笑迪. 高光束质量宽带OPCPA关键技术研究[D]. |
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