周期量级超短激光脉冲传播及量子相干控制光谱效应研究
文献类型：学位论文
| 作者 | 宋晓红 |
| 学位类别 | 博士 |
| 答辩日期 | 2005 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 徐至展 |
| 关键词 | 周期量级超短激光脉冲 量子相干控制 载波拉比振荡 自相位调制 |
| 其他题名 | Propagation and Coherent Control of Spectral Effects for Few-cycle Laser Pulses |
| 中文摘要 | 周期量级超短激光脉冲与物质相互作用研究是当今强场激光物理领域的热点研究方向，量子相干控制也是国际上近年来兴起的前沿研究领域，周期量级超短激光脉冲与物质相互作用中的量子相干控制研究作为交叉前沿，具有重要的科学意义和潜在的应用价值。本学位论文对极端非线性光学条件下，尤其是周期甚至亚周期量级超短脉冲与物质相互作用中的量子相干控制光谱以及超短激光脉冲传输中的时空耦合等特性进行了系统的研究，取得了一系列创新性研究成果。这些成果主要包括：1．首次探讨了亚周期阿秒脉冲在高密度二能级介质中的面积演化特性。研究发现，由于亚周期阿秒脉冲强的载波拉比振荡效应及载波自相位调制的影响，脉冲载波发生明显调制，透射光谱中有明显的高频成分产生，自感应透明现象消失。对于非整数倍脉冲，脉冲在传播过程中也不趋向于阮自感应透明，透射光谱中仍有高频成分产生。而且，产生的高频成分与脉冲面积密切相关，面积越大，高频成分越明显。因此，对于亚周期阿秒脉冲来说，面积定理完全失效。2．提出了利用双色场相对相位控制实现二能级介质中小面积激光脉冲透射光谱中高频成分产生的新方案。研究发现，即使对于小面积超短激光脉冲，由于双色场之间的相干作用，其透射光谱中也会有高频成分产生。而且透射光谱与初始相对相位密切相关。采用适当的双色场组合脉冲，通过控制双色场之间的相对相位，能够选择性地产生连续或分立的高频成分。3．研究了周期量级超短激光脉冲惆啾量子相干控制光谱效应。发现其光谱特I性与初始啁啾密切相关：对于啁啾率比较小的情况，正啁啾对应光谱蓝移，负啁啾对应红移。然而，当啁啾率比较大时，正啁啾脉冲使介质透明，而负啁啾则使光谱中出现明显的高频成分。4．将周期量级超短激光脉冲与二能级介质的相互作用推广到简并三能级介质中，并分析讨论了其光谱的演化行为。研究发现，在简并系统中产生高频成分所需要的激光脉冲强度大大降低。而且，当激发态之间的频率间隔增大时，自感应透明现象不能实现，脉冲光谱发生明显分裂。5．最后，探讨了电离效应对周期量级超短激光脉冲在二能级介质中传播的影响。结果表明，当电离现象主要由脉冲峰值处的载波引起，且电离的粒子数比较少时，电离效应对脉冲传播的影响主要表现在对分裂的小脉冲的吸收上，其光谱在跃迁频率附近的振荡现象减弱，但产生的高频成分基本没有影响。但当粒子被完全电离时，高频成分的产生明显受到抑止，即使增大脉冲面积，产生的高频成分也不会相应增多。 |
| 英文摘要 | The interaction of few-cycle ultrashort laser pulses with matter is currently being a hot subject in the high intensity laser physics. Quantum coherent control is also a frontier area arisen in recent years. As an intersection frontier, coherent controls with few-cycle laser pulses have great academic significance and application potentials. This dissertation conducts a series researches in the coherent control of spectral effects and propagation properties under extreme nonlinear optics condention, especially with few-cycle and subcycle ultrashort pulses. The main innovative results are as follows: 1. We firstly investigate the propagation of subcycle attosecond pulse in a dense two-level media. It is found when subcycle attosecond pulse is considered, that ideal self- induced transparency can not occur even for 2n pulse, significantly higher spectra components can occur due to the enhanced carrier-wave Rabi floppings and carrier self-phase-modulation While the pulses whose areas are not integer multiples of 2rc can not evolve to 2n self- induced transparency as predict by the standard area theorem. Higher spectral components can also occur in this case. Moreover, these higher spectral components relate sensitively to the pulse area: the larger the pulse area is, the more evident these higher spectral components are. Hence, the area theorm fully breaks down for subcycle attosecond pulse. A new method to generate higher spectral components with small area laser pulses is provided. It is found that higher spectral components can be produced even for small area laser pulses due to the interference effect of the two laser pulses. Moreover, deferent superposition of the combined laser pulses corresponds to different features of these higher spectral components. Using proper two-color combination, continuous and distinct higher spectral components can be achieved by adjusting the relative phase. We investigate the coherent control of spectra effects with chirped femtosecond laser pulse propagating in a two-level-atom medium. It is found that the spectral feature depends crucially on the sign and magnitude of the initial chirp rate. For small chirp rate, blueshift or redshift of the spectrum can occur depending on the sign of the chirp. However, for relative large chirp rate, the medium can become transparent to positive chirped laser pulse, whereas in the case of negative chirped laser pulse, higher spectral components can be produced even for small area laser pulses. We make a further study of propagation and spectral effects of few-cycle ultrashort laser pulse in a degenerate two-level system. It was found that the necessary intensity to produce higher spectral components will be much lower in this system. Moreover, when increase the level spacing between the two excited states, self-induced transparency can not occur, obvious spectra splitting can be found. We also carry out a numerical investigation of the influence of photoionization on the propagation and spectral effects of few-cycle laser pulse in a two-level system. It is found when the fractional ionization is weak, that the impact of ionization on the propagation of few-cycle laser pulse mainly manifest in the absorption of the small splitting pulse, while higher spectral components make no difference. However, when the ionization is enhanced, higher spectral components are no longer increase even for larger pulse area. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15847]  |
| 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 | 宋晓红. 周期量级超短激光脉冲传播及量子相干控制光谱效应研究[D]. 中国科学院上海光学精密机械研究所. 2005. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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