量子相干控制原子、分子超快多光子非线性效应研究
文献类型：学位论文
| 作者 | 杨玮枫 |
| 学位类别 | 博士 |
| 答辩日期 | 2007 |
| 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 | 载波包络相位 固有偶极矩 多光子粒子数累积 四波混频 |
| 其他题名 | Coherent control of ultrafast multiphoton nonlinear processes in atomic and molecular media |
| 中文摘要 | 量子相干控制是国际上近年来兴起的前沿研究领域，超短激光脉冲与物质相互作用研究也是当今强场激光物理领域的热点研究方向。超快量子相干控制，特别是极端超快非线性光学条件下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。 本学位论文重点是瞄准极端非线性光学条件下，尤其是对周期量级超短激光脉冲量子相干控制原子、分子多光子非线性效应以及周期量级超短激光脉冲传播过程中的时空耦合特性等进行了系统的研究，取得了若干创新性研究成果。主要包括： 1.首次探讨了超短激光脉冲链在二能级极化分子系统中诱导产生相干多光子粒子数累积效应。研究发现，由于固有偶极矩的存在，脉冲链中两个连续激光脉冲之间的量子干涉被放大，在非固有偶极系统中不可能发生的相干多光子粒子数累积效应能够在极化分子中产生。而且，脉冲间的相对相位对这种粒子数累积效应有重要的影响，研究结果表明，在N光子跃迁中，最大的粒子数累积发生在相对相位周期等于2pi/N时。 2.提出了利用双色场载波包络相位控制二能级极化分子介质中超快四波混频效应的新方案。研究发现在极化分子介质中，即使采用较低电场强度的周期量级超短激光脉冲，也能产生超快四波混频的放大。而且，由于脉冲之间的干涉作用，对于不同载波包络相位组合，其组合电场的时间形状有很大不同，当组合电场峰值与固有偶极矩方向反向时，四波混频转换效率比同向时放大超过10倍。因此，可以通过采用不同载波包络相位的双色场组合实现对超快四波混频的有效操控。 3.首次研究了极化分子介质中周期量级超短激光脉冲的载波包络相位相关现象。发现，在极化分子介质中，由于固有偶极矩的存在会对介质的宏观极化产生重要影响，从而导致激光脉冲在传输过程中产生一个类孤子脉冲。而且，产生的类孤子脉冲的脉宽和强度等主要特征强烈的依赖于输入激光脉冲的载波包络相位。这一发现为低强度下的周期量级超短激光脉冲载波包络相位测量提供了新的有效途径。 4.探讨了在二能级固有偶极矩的量子系统中合成阿秒脉冲的新方法。由于固有偶极矩的作用，高次谐波平台可以被拓宽至X射线区。而且，由于在这一系统中产生的偶次和奇次谐波都可用于合成阿秒脉冲链，从而能够产生更高强度的阿秒X射线脉冲。 5.分析了五能级原子系统中的双暗态相互作用诱导高效率四波混频产生。发现即使在不满足多光子共振条件时，在两个电磁感应透明窗口中都能产生四波混频放大。而且，由于双暗态相互作用的存在，可以操控放大任意一个电磁感应透明窗口中的四波混频转换效率。 |
| 英文摘要 | Coherent control is a frontier area arisen in recent years. The interaction of ultrashort laser pulses with matter is also currently a hot subject in the high intensity laser physics. As an intersection frontier, ultrafast coherent controls under extreme nonlinear optics condition (few-cycle ultrashort laser pulse) have great academic significance and potential application. This dissertation mainly conducts a series of researches in the ultrafast coherent control of multiphoton interactions with ultrashort and few-cycle ultrashort laser pulses, and propagation properties under extreme nonlinear optics condition. The main innovative results are as follows: 1.We investigate, for the first time to our knowledge, coherent population accumulations of multiphoton transitions induced by an ultrashort pulse train in a two-level polar molecule. It is demonstrated that the quantum interference between two sequential laser pulses can be enhanced because of the effects of permanent dipole moments (PDM). Coherent population accumulation of multiphoton transitions, which can not occur in non-dipole systems, can be achieved in the polar molecule. Moreover, the population accumulations depend crucially on the relative phase between the pulses, and the maximum population accumulation occurs in a relative phase period 2pi/N in N-photon transitions. 2.A new method to control of ultrafast four-wave mixing (FWM) in polar molecule medium with the carrier-envelope phases (CEP) of two-color few-cycle ultrashort laser pulses is proposed. It is found that due to the effects of PDMs, the enhancement of ultrafast FWM can be produced even without high field intensities. Moreover, the conversion efficiency of FWM can be controlled by the arrangement of CEPs because the temporal shape of electric field is modified by the interference between the two-color few-cycle pulses, and when the oscillation peak antiparallel to the PDMs reaches a maximum, the intensity of FWM generated wave can be enhanced almost 10 times. 3.We investigate a few-cycle ultrashort pulse propagating in a polar molecular medium. It can be demonstrated that the coherent polarizations are greatly modified and a solitonlike pulse can be generated due to the effects of PDMs. Moreover, the main features of the solitionlike pulse, such as pulse duration and intensity, are related to the CEP of the incident pulse. In other words, these results illustrate that there is a certain correlation between the CEP of the incident pulse and the temporal properties of the solitionlike pulse, which might be helpful to provide a new means of measuring the CEP of few-cycle ultrashort pulse at relative low intensity. 4.The generation of attosecond pulses in a two-level system with PDMs is investigated. It is shown that due to the presence of PDMs, the plateau of the high-order harmonic generation spectrum can be extended to x-ray range. Moreover, attosecond x-ray pulses with higher intensity can be synthesized by using both even and odd harmonics because of their quantum interference. 5.We analyze a FWM scheme in a five-level atomic system in which double-dark resonances are present. It is found that the enhancement of FWM in both electromagnetically induced transparency (EIT) windows can be obtained even without the condition of multiphoton resonance. Moreover, the conversion efficiency of FWM in one EIT window can be much larger than that in the other due to the presence of interacting dark resonances. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15557]  |
| 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 | 杨玮枫. 量子相干控制原子、分子超快多光子非线性效应研究[D]. 中国科学院上海光学精密机械研究所. 2007. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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