| 题名 | 高通量条件下的光束匀滑技术研究 |
| 作者 | 姜有恩 |
| 学位类别 | 博士 |
| 答辩日期 | 2013 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 林尊琪 |
| 关键词 | 激光辐照均匀性，光谱色散，焦斑整形，体位相调制器，频幅调制转换效应 |
| 其他题名 | Research of Beam Smoothing Technologies Used under High- Fluence Conditions |
| 中文摘要 | 在激光惯性约束聚变的内爆过程中，靶面辐照的均匀性是实现成功点火的必要条件。不同的驱动方式，对靶面辐照的均匀性有不同的要求。本课题以满足间接驱动以及直接驱动的辐照均匀性需求为目标牵引，重点解决时间域匀滑技术在高通量条件下的工程应用问题，完成时间域匀滑技术方案的优化设计，实现光谱的精确控制，以及建立辐照均匀性的综合评价机制等。完成的主要工作内容包括以下几个方面： 1) 提出了采用不同方向的空间功率谱来分析远场的焦斑分布，以消除现有的径向空间功率谱算法对峰值频谱的平均效应，并在透镜列阵结合光谱色散的实验中得到了有效地验证。在时间尺度上分析匀滑效果，提出采用焦斑不均匀性的渐进时间 和目标时间 两项参数，来评价光束匀滑的技术方案，并给出了降低这两种参数的途径。 2) 基于激光经过光谱色散后在时间、空间域的电场理论模型，以及在空间、频率域的角谱理论模型，完成了一维光谱色散、一维多频调制和两维光谱色散在神光Ⅱ装置中应用的具体方案设计、模拟计算和结果对比。 3) 首次完成了一维光谱色散和透镜列阵相结合的光束匀滑在线实验研究。在引入基频光谱带宽为0.3nm、三倍频终端线色散为24.9倍衍射极限的光谱色散后，能量集中度为80%区域的焦斑辐照不均匀性从46%下降至17%，并且没有改变焦斑初始的集中度。根据焦斑的空间功率谱分析，在色散方向上，空间干涉频率所对应的功率谱幅值下降了约20dB，正交方向相应的幅值下降了约10dB。因此，一维光谱色散匀滑技术可以十分有效地抑制透镜阵列多光束相干所对应的空间频谱成分，若拓展到两维光谱色散可进一步提高焦斑的均匀性。 4) 完成一维光谱色散分别结合分布式位相板和连续位相板的在线实验研究。分析了单频调制色循环达到2.49时的空间频谱峰值分布，并验证了采用双频调制可以抑制因为色循环大于1所引起的峰值频谱，抑制率约为10dB。实验结果表明，在光谱线色散量与连续位相板整形焦斑的直径比达到30%的情况下，对于焦斑能量集中度有较为明显的影响。 5) 国内首次成功地研制出高频、高效率的谐振腔式体位相调制器，包括：工作频率3.25GHz、通光口径5×5（mm）和工作频率10.3GHz、通光口径2×3（mm）的两种调制器。提出了通过优化的速度匹配条件，来提高调制效率。对于3.25GHz的调制器，微波相速度实际估算值约为光波的1.5倍，相比于严格的速配匹配条件，将调制器的效率提高了约12.8%。在微波脉冲峰值功率为1kW的条件下，脉宽3ns、波长1053nm的窄带激光单程通过该调制器后带宽被展宽至0.13nm。而10.3GHz的调制器在双通调制情况下，将窄带激光的光谱展宽至0.7nm。并提出了实现调制频率源的位相和激光波形前沿同步锁定的方案，并通过采用率12GHz的任意波形发生器完成方案的基本验证。 6) 提出了两种频幅调制转换效应反补偿的新方案。在频率域，利用了双折射效应实现类似于F-P标准具的光谱滤波效应：通过调节晶体上的电压实现光谱透射函数中心波长的精确调节，另一方面通过改变偏振方向实现透射函数精细度的精确控制。该方案可以采用光纤实现器件的输入输出的集成，并完成了光谱透射函数基本的实验验证。在时间域，提出了利用高速任意波形发生器，直接对初始的时间波形反补偿的方案。模拟结果显示，该方法可以有效补偿系统的频幅调制转换效应。 |
| 英文摘要 | In inertial confinement fusion (ICF) experiments, uniform irradiation on the target is an essential condition for successful ignition. The requirements of irradiation uniformity depend on the drive approaches. The research aim is to fulfill the irradiation uniformity requirements of the indirect drive and direct drive. The main work is focused on engineering applications of the time-domain smoothing technology in high-fluence conditions, including optimizing the design of time-domain smoothing, precisely controlling of the laser spectrum, and establishing a comprehensive evaluation of laser irradiation uniformity. The main research work could be summarized as follows: 1) To eliminate the average effect of spectral peaks by radial spatial power spectrum (PSD) analysis, a scheme of PSD in different directions is proposed to analyse the intensity distribution of the far-field irradiation. This new approach is verified in the beam smoothing experiment utilizing spectral dispersion and lens array (LA). Asymptotic time ( ) and aimed time ( ) are proposed to evaluate the irritation non-uniformity on the time scale. The method of reducing these two parameters is also given. 2) Base on the laser electrical field model in time and spatial domain and the angular spectrum in the frequency and spatial domain, the design of one-dimensional spectral dispersion (1D SSD), 1D multi-frequency modulation (Mult-FM) SSD and two dimensional (2D) SSD is simulatied and compared. 3) The effectiveness of beam smoothing utilizing 1-D SSD and LA is firstly verified by online experiment in the ninth beam of SG-Ⅱ. Using 3ω spectral dispersion with 270-GHz bandwidth and line dispersion of 24.9 times the DLW, normalized focal spot non-uniformity of an 80% energy concentration is decreased from 46% to 17%. The encircled energy fraction is not affected by 1-D SSD. For the first four peak spectra, suppression ratio of 20dB and 10dB are achieved in the dispersion direction and in the orthogonal direction, respectively. Thus, the peak spectra caused by multiple beam interference of the LA are effectively reduced by use of 1-D SSD. Furthermore, if another orthogonal-direction SSD is added, higher uniformity could be expected. 4) The performance of 1D SSD combined with the distribute phase plate (DPP) and continuous phase plate (CPP) is investigated. Theoretical predictions of peak spectra caused by SSD’s color cycles of 2.49 are in excellent agreement with the experimental results. With double-frequency modulation, the amplitude of these peak spectra is reduced by ~10dB. When the ratio of spectral line dispersion to the spot diameter reached ~30%, the encircled energy fraction of the CPP is obviously affected 5) High-frequency, high-efficiency bulk electric-optics (EO) phase modulators utilizing microwave resonant design in lithium niobate are successfully developed, including a 3.25-GHz modulator with optical aperture of 5×5 (mm) and a 10.3-GHz modulator with optical aperture of 2×3 (mm). Increasing the modulation efficiency by optimizing the velocity-matching condition is propsed. In the 3.25GHz modulator, microwave phase velocity is approximately 1.5 times of the laser velocity. Compared to a rigid-velocity-matched design, modulation efficiency of this special design is higher by about 12.8%.Using this modulator in a single-pass configuration with 1kW microwave drive power, the spectral bandwidth of a 1053-nm, 3-ns pulse-length laser is broadened to 0.13 nm. With a double-pass configuration in the 10.3GHz modulator, spectral bandwith of the same laser pulse is broadened to 0.7nm. A scheme to achieve synchronization locking between the leading-edge of laser pulse and the phase of the RF source is propsed. And the effectiveness is verified by using an arbitrary wavefrom generator (AWG) with a shampling rate of 12GHz. 6) New approaches to suppress the frequency modulation to amplitude modulation conversion (FM-to-AM) are propsed. In the frequency domain, birefringent effect is used to achieve the spectral filtering effect similar to a Fabry–Pérot (FP) etalon. The center wavelength of the transmission function could be precisely adjusted by the voltage applied on the EO crystal. Meanwhile, the fineness of the transmission function could by adjusted by the controlling the polarization direction. The element could be integrated by fiber optics, and the preliminary experimental verification of the spectral transmission function is completed. In the time domain, a scheme of directly compensation of the temporal pulse by using high-speed AWG is also propsed. The simulation results show that this method could effectviely compensate the FM-to-AM. |
| 语种 | 中文 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15737]  |
| 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 | 姜有恩. 高通量条件下的光束匀滑技术研究[D]. 中国科学院上海光学精密机械研究所. 2013. |
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