氦原子瞬态吸收光谱的阿秒啁啾效应研究
文献类型：学位论文
| 作者 | 赵海文 |
| 文献子类 | 硕士 |
| 导师 | 曾志男 |
| 关键词 | 阿秒脉冲 Attosecond pulse 泵浦-探测 Pump-probe 瞬态吸收谱 Transient absorption 啁啾效应 Chirp effect 双光子过程 Two-photon process |
| 其他题名 | Attosecond chirp effect on the transient absorption spectrum of laser-dressed helium atom |
| 英文摘要 | 电子运动的时间尺度从几个飞秒（10-15 s）到几十阿秒（10-18 s），对这些电子运动的了解是认识宏观世界的基础。这些超快的动力学过程用传统的飞秒激光脉冲是无法分辨的。然而，过去的二十年里，基于高次谐波产生过程（HHG），几百个阿秒甚至更短的单个脉冲的产生技术已日趋成熟。单个阿秒脉冲的出现提供了前所未有的时间分辨率去研究超快的电子动力学过程。阿秒脉冲与传统泵浦-探测吸收光谱的结合催生了全新的阿秒瞬态吸收光谱（ATAS）技术，它能够同时提供超高的时间分辨率和多能级测量。利用这种技术人们观测到一系列新奇有趣的现象。 由于阿秒脉冲的高次谐波产生过程，其光谱相位会随着驱动激光电场的强度迅速变化，因此啁啾是阿秒脉冲的固有属性。但是以往关于ATAS的理论研究都忽略了阿秒脉冲的啁啾特性。 本论文工作瞄准阿秒瞬态吸收光谱技术的研究热点，重点研究了阿秒脉冲的啁啾特征对氦原子瞬态吸收光谱的影响。主要研究内容和成果包括以下几个方面： 1.通过数值求解三维含时Sch?rdinger方程（3D-TDSE），我们分别计算了不同阿秒啁啾下氦原子的单电子响应函数。我们第一次观察到瞬态吸收谱的阿秒啁啾效应：不同啁啾的吸收曲线沿延时的方向发生相对平移，平移量不仅和阿秒的啁啾参数有关，还和极紫外光子能量、红外激光脉冲波长有关。 2.基于简化的三能级模型，我们近似求解了偶极矩谱的解析表达式，发现了双光子吸收过程的存在，提出了非直接的双光子吸收模型。通过分析模型和时-频分析工具，我们很好地重现了阿秒啁啾效应。; Electronic dynamic in atoms typically occur on a few-femtosecond (10-15 s) or sub-femtosecond (10-18 s) timescale. The acknowledgement of these electronic motions is the basis for understanding the macroscopic world. These processes are too fast to be resolved by ordinary femtosecond optical laser pulses. However, in the past ten years, techniques related to high harmonic generation to generate isolated pulses with durations of a few hundred attosecond, or even shorter, have been established. These isolated attosecond pulses provide unprecedented opportunities to study ultrafast electron dynamics. The combination of attosecond pulses and conventional pump-probe absorption spectroscopy gave birth to attosecond transient absorption spectroscopy (ATAS), which can simultaneously provide ultrahigh time resolution and multi-level measurement and a series of novel phenomena have been observed. To date, theoretical researches on ATAS are all focused on the use of a chirp-free attosecond pulse and the chirp characteristic of attosecond pulse has been ignored. Nevertheless, chirp is difficult to eliminate in attosecond pulse generated by high harmonics due to the intrinsically laser-intensity-dependent dipole. The aim of the dissertation is concentrated on how the attosecond chirp influences the transient absorption spectrum of laser-dressed helium atom. The main results and innovations include: 1.By numerically solving the fully time-dependent three-dimensional time-dependent Schr?dinger equation (3D-TDSE), we calculated the single-electron response function of laser-dressed helium atom with different attosecond chirp rates. We first observed the temporal shift of absorption curves with varying the chirp rate, together with the shift distance dependent on the absorption line energy of the observation and infared laser wavelength. 2.We approximately derive an analytical expression for the dipole-moment spectrum based on the three-level model. It implies two-photon process. Then we propose an indirect two-photon process and quantitatively interpret the above simulation results by time-frequency analysis. |
| 学科主题 | 光学工程 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/30914]  |
| 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 | 赵海文. 氦原子瞬态吸收光谱的阿秒啁啾效应研究[D]. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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