泵浦光特性与OPCPA结构对光参量啁啾脉冲信噪比影响研究
文献类型：学位论文
| 作者 | 潘雪 |
| 学位类别 | 博士 |
| 答辩日期 | 2011 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 李学春 |
| 关键词 | 光参量啁啾脉冲放大OPCPA 惯性约束核聚变ICF 信噪比 自发辐射光放大ASE 参量荧光 超短脉冲光参量放大SPOPA 孔径耦合带状线ACSL 啁啾脉冲堆积 交叉偏振波XPW 脉冲复制环 |
| 其他题名 | Research on the impact of pump characteristic and structure on Optical Parametric Chirped-Pulse Amplification contrast |
| 中文摘要 | 时域信噪比（又称时间对比度）定义为在主脉冲前一定时域范围内脉冲峰值光强与预脉冲或自发辐射光放大ASE背景光强的比值，是超强超短激光系统最主要的难题之一。由于在超短超强激光脉冲打靶实验中，预脉冲或主脉冲底座在强度达到1012W/cm2时就会使靶物质气化或产生预等离子体，在主激光脉冲到来之前会改变靶物质的状态，从而影响作用过程或改变作用机制，因此信噪比成了制约快点火实验的瓶颈，必须采取相应措施提高超短激光脉冲的信噪比。国内用于快点火的钕玻璃神光II皮秒拍瓦激光驱动器装置输出峰值功率密度能够达到1020W/cm2，根据激光与物质相互作用时间为10ps，最终输出需要主脉冲前10ps以外的信噪比要大于108，由于噪声主要产生于高增益的两级纳秒域光参量啁啾脉冲放大（OPCPA）前端预放装置，针对影响OPCPA信噪比的主要因素，本课题致力于研究泵浦光特性以及OPCPA结构对OPCPA信噪比的影响，期望能够满足输出要求，具体开展了以下几方面的工作： 首先研究了泵浦光特性对OPCPA信噪比的影响。对泵浦光中ASE噪声如何通过参量作用导致信号光光谱振幅和相位调制，最终形成噪声底座进行理论估算，与数值模拟结果完全吻合，并利用此模型预测将噪声底座压缩到主脉冲10ps范围内的泵浦光ASE噪声频谱宽度。结合数值模拟模型，进一步分析了泵浦光中ASE光谱宽度，振幅调制深度（ASE的噪声功率），参量作用过程中的饱和程度以及同时考虑参量荧光对压缩后信噪比的影响，改善OPCPA结构采用ps域短脉冲参量放大SPOPA和ns域OPCPA相结合的双级OPCPA方法，并分别指出了两级泵浦源的具体设计指标。 然后实验中采用钕玻璃再生放大器和四程同轴放大器相结合的方法，经过缩束倍频得到了百皮秒毫焦耳超短脉冲泵浦输出，为ps域SPOPA所需的亚皮秒毫焦耳高功率密度的泵浦光源的实现提供了实验平台和技术支持，此方法可以通过提高注入种子光能量，即提高注入种子光对比度，降低ns域OPCPA的增益，从而减小纳秒时域范围内的参量荧光。同时对于ns域OPCPA的泵浦源进行改进，实验上在泵浦源系统增益最高的钕玻璃再生放大器中采用光谱滤波装置，有效地减小了泵浦光中ASE光谱宽度和ASE噪声功率，从而减小压缩后ASE噪声底座宽度和噪声强度。在对泵浦光进行时域整形的同时，在参量作用中为了实现泵浦光和信号光的高精度同步，泵浦光中采用啁啾光脉冲堆积代替孔径耦合带状线（ACSL）的新型前端集成波导电光调制时域整形技术，实现了整形泵浦光脉冲和超短亚皮秒种子脉冲的高精度同步。此外，泵浦光中新的整形技术相当于任意波形发生器，在OPCPA过程中可以对放大的信号光进行任意光谱整形，与在参量作用之前对种子光的光谱整形进行对比，它不会引入光谱相位调制，而且光谱整形和能量放大可以同时进行，通过数值模拟从理论上分析了两种方案对泵浦光稳定性的具体要求。 针对国内外普遍采用的非线性脉冲清洁技术，由于实验条件的限制，我们重点从理论上分析了交叉偏振波产生（XPW）非线性滤波器原理，研究了影响XPW滤波能量转化效率的因素，对滤波器结构进行改善，采用双级晶体装置能够提高能量转化效率。同时对注入信号光的高阶频谱相位对XPW输出脉冲宽度、谱宽以及相位的影响进行数值模拟，为XPW的实验提供了理论依据。 为了满足利用PIN管与示波器来实现100：1的高信噪比惯性约束核聚变（ICF）脉冲探测的需要，我们采用光纤脉冲复制环装置将单发脉冲信号变为幅度指数递减的脉冲序列，然后采用累加平均的方法可以有效地提高ns脉冲单次测量的动态范围。 |
| 英文摘要 | Temporal signal-noise-ratio(also contrast) defined as the intensity ratio between the peak intensity of the main pulse and the intensity of any prepulses and amplified spontaneous emission (ASE) in a given temporal range before the main pulse，which is one of the major difficulties in the development of ultraintense and ultrashort laser system. For high-field physics experiment, preplasma will product when the intensity of ASE nanosecond background as well as short prepulses reach 1012W/cm2, which lead to physical modification of solid target prior to the arrival of main pulse, so the temporal contrast of pulses is one of the main bottleneck for application of ultra short and ultra-intense lasers in high-field physics, and some techniques must be adopted to improve temporal contrast. ShenGuang II-Petawatt(SGII-PW) project output focal intensity can be achieved above 1020W/cm2 on a solid target, considering the preplasma-creating time, it implies that a peak intensity to prepulse intensity contrast of > 108 which is located at 10 picosecond before main pulse. Because noise is mainly generated from the high-gain two-stage optical parametric chirped pulse preamplifier(OPCPA), this thesis mainly focus on the impact factors on the contrast degration of OPCPA, especially on the pump characteristic and OPCPA structure: This article commences with the analysis of pump-pulse characterist-induced contrast degration in an OPCPA system. A simple analysis was presented to estimate both the contrast ratio of the background noise and the duration of its pedestal, and this estimate compares well with the results of numerical simulation. We predict the pump ASE spectrum width when duration of ASE pedestal is decreased to 10 picosecond before main pulse. The impact of pump ASE noise spectrum, ASE noise power, saturation degree during parametric amplification and parametric fluorescence on OPCPA contrast were analyzed by numerical simulation results, OPCPA structure was improved to dual OPCPA , which is ps short pulse optical parametric amplifier(SPOPA)combined with ns long pulse optical parametric amplifier(OPCPA)，and design guideline of two pump pulse were pointed out. Then 100 picosecond microjoule high intensity pump pulse was achieved in the experiment through Nd:glass regenerative amplifier combined with four-pass power amplifier and frequency doubled, which provide experiment plat roof and technology support for carrying out subpicosecond microjoule high intensity pump pulse. It can increase the input seed pulse energy and improve the seed pulse contrast, then to alleviate the gain in the nanosecond OPCPA preamplifier in order to decreasing the nanosecond PF which is limited in the range of pump temporal duration. Meanwhile, the pump of nanosecond OPCPA was improved, significant reduction of induced temporal pedestal and noise power was experimentally demontrasted in the OPCPA system by filting the pump ASE spectrum and ASE noise power in a Nd:glass regenerative amplifier. To ensure high precision synchronization between temporal shaping pump pulse and signal pulse, a new method for electrical waveform generation based on chirped pulse stacker instead of aperture-coupled-stripline (ACSL) in intensity modulation pulse shaping is provided, as a means for high precision synchronization between shaped pump pulse and signal pulse in OPCPA. Furthermore, new pulse shaping technology as arbitrary waveform generator used in pump can achieve arbitrary spectral shaping using OPCPA, related to the spectral shaping method for chirped seed pulse before optical parametric amplification, it can not bring the spectral phase modulation, and the procedure of spectral shaping and energy amplified go on in the same time, the detailed requirement for pump stability is analysed from the numerical simulation results. Based on many nonlinear pulse cleaner technology, we theoretically study on the Cross-polarized wave (XPW) generation filter for the limitation of experiment, the principle of XPW filter is introduced, and the impact factors on XPW energy conversion efficiency are analysed, then the conversion efficiency was enhanced by two crystal arrangement. Meanwhile the numerical simulation model of the influence of XPW pulse width，spectrum and phase with initial quadratic and third-order spectral phase is presented and analysed, it provide the theoretical support for XPW experiment. To meet the need of 100:1 high dynamic range inertial confinement fusion(ICF) pulse measurement by PIN diode with oscilloscopes, A fiber pulse replication loop system is developed for generating temporal replicated pulse train with an exponential decay curve, and averaged with itself to reduce the noise and improve measured dynamic range. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15670]  |
| 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 | 潘雪. 泵浦光特性与OPCPA结构对光参量啁啾脉冲信噪比影响研究[D]. 中国科学院上海光学精密机械研究所. 2011. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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