基于气体高次谐波的阿秒脉冲产生及控制理论研究
文献类型：学位论文
| 作者 | 于永丽 |
| 学位类别 | 博士 |
| 答辩日期 | 2010 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 程亚 |
| 关键词 | 高次谐波 超短激光脉冲 双色偏振时间门 阿秒脉冲 |
| 其他题名 | Theoretical Study on Generation and Control of Attosecond Pulses from High-order Harmonic Generation of Gas |
| 中文摘要 | 超强超短激光技术的发展，促使人们对微观世界的时间尺度认知进入阿秒量级。阿秒脉冲光源成功实现为超快探测技术带来了前所未有的时间分辨率，并开辟了阿秒时间尺度原子分子内部电子超快动力学过程的研究，将在物理、生物、化学、材料等方面有着广泛且重要的应用。 当前实验上实现的阿秒脉冲产生主要是基于高次谐波辐射过程。但现有的XUV阿秒脉冲产生技术能够获得的单个阿秒脉冲的能量非常低，不能达到实用的要求。发展新的高强度的单个阿秒脉冲产生技术，提高阿秒脉冲的产生效率，获得更短的阿秒脉冲光源仍是当前阿秒物理的核心问题之一。 本论文工作瞄准获得阿秒超快脉冲这一前沿课题，集中开展高次谐波和阿秒脉冲光源的产生及控制研究，并进一步探索阿秒脉冲产生的新方案。主要工作内容及成果如下： 1.利用强场近似模型，开展了双色偏振激光场与惰性气体作用获得XUV阿秒脉冲辐射的理论研究。首先，提出了偏振方向垂直的周期量级双色场偏振门方案。通过分析电子在激光场中的运动轨迹，发现部分电离电子可以返回到母核附近，产生了XUV超连续谱辐射，在时域上表现为一阿秒脉冲链，且各阿秒脉冲的偏振方向不同。通过截取高能量的高次谐波谱，则可以得到单个阿秒脉冲。其次，提出了椭圆偏振激光脉冲与线偏振激光脉冲组成的长脉冲的双色场偏振门方案。研究了高次谐波辐射情况，及阿秒脉冲产生条件，并发现在长脉冲的双色场偏振门方案中仍然可以产生单个阿秒脉冲辐射。2.利用强场近似模型，开展了高效率的XUV超连续谱产生理论研究。首先，提出了以周期量级正弦激光脉冲代替传统的余弦激光脉冲作为主驱动脉冲的的双色场方案，结果发现双色正弦组合激光场驱动产生的阿秒脉冲强度比在双色余弦组合激光场中所产生的阿秒脉冲强度提高了两个数量级。其次，构造了半周期的800nm激光脉冲及半周期的2400nm激光脉冲组合而成的特殊激光场，通过控制两脉冲之间的时间延迟、相对位相，可以使电子在前半周期充分电离，在后半周期激光场中经过较长加速时间后被拉回母核。结果表明电子既在激光场中获得了大的动能扩展了高次谐波的截止能量，又提高了高次谐波的转化效率，从而产生了高强度的单个阿秒脉冲。3.利用扩展的Lewenstein模型，开展了双色偏振时间门与双原子分子相互作用高次谐波辐射的理论研究。研究了双色场偏振门下N2、O2分子不同分子取向时产生的高次谐波，比较了不同分子轨道对阿秒脉冲产生的影响。研究了N2分子高次谐波与其参考原子产生的谐波相比较的情况，发现双色偏振门与N2结合可以有效的抑止阿秒脉冲链的产生，更利于产生单个阿秒脉冲。 |
| 英文摘要 | The development of ultraintense and ultrashort laser technology now allows us to produce extremely short coherent light pulses with a duration at attosecond (1 attosecond=10-18s) time-scale. Attosecond coherent light source facilitates an unprecedented time resolution for ultrafast measurement, thereby enabling investigation of ultrafast processes inside atoms and molecules. For this reason, attosecond technology will have great potential to be widely used in the resaerch fields such as physics, chemistry, biology, and material sciences. So far, attosecond pulses are mostly obtained experimentally based on the high order harmonic generation from noble gas. However, as a highly nonlinear process, high order harmonic generation is intrinsically inefficient. Therefore, the intensity of an isolated single attosecond XUV pulse obtained with current attosecond technology is too low for many practical applications. Until now, exploring new technologies to generate high intensity attosecond XUV pulse and shortening the current XUV pulse duration is still critical for of attosecond physics. Aiming at generation of intense and extremely short (e. g, <100as) the attosecond pulses, we concentrate on the development of novel technologies for broadening the bandwidth of supercontinua which supports the formation of attosecond pulses, as well as increasing the conversion efficiency of attosecond pulse generation. The main results are listed as follows: 1. Based on the strong field approximation model, we theoretically demonstrate the generation of extreme ultraviolet supercontinua when noble gas exposed in a two-color polarized gated field. First, in an orthogonally polarized two-color few-cycle laser field, we show that the ionized electrons can be driven back to their parent ions after traveling along curved trajectories in a plane perpendicular to the beam propagation direction, giving rise to a train of attosecond pulses at different polarization angles. A single isolated attosecond pulse can be obtained by blocking the low-order high harmonics. Second, in a two-color multi-cycle polarization gating consisting of an elliptically polarized laser field and a linearly polarized laser field, we investigate the high harmonic generation and show that an isolated attosecond pulse can be obtained. 2. Based on the strong field approximation model, we theoretically investigate the efficient extreme ultraviolet supercontinuum generation. First, we propose a method for generating an intense single attosecond pulse by superposing a weak sub-harmonic pulse upon a sine-waveform few-cycle driving pulse instead of the traditionally used cosine waveform counterpart, leading to an increase of efficiency by nearly two orders of magnitude in single attosecond pulse generation as compared with the use of a cosine-waveform field. Second, in the laser field synthesized by a half-cycle fundamental wave (800nm) and a half-cycle subharmonic wave (2400nm), by controlling the time delay and relative phase between the two pulses, the electrons can be ionized sufficiently in the former half-cycle and be drived back to their parent ions in the latter half-cycle laser field. The results show that the cutoff energy is extended and the harmonic conversion efficiency is enhanced. Therefore, an efficiently isolated attosecond pulse is obtained. 3. Based on the extended Lewenstein model, we theoretically investigate high order harmonic generation from the diatomic molecules in an orthogonally polarized two-color few-cycle optical field. The dependence of high-order harmonic generation on the orientation of molecules and the effect of different molecular orbitals on the attosecond pulse generation have also been investigated. The results show that the combination of N2 and two-color polarization gating can significantly suppress undesirable satellite pulses comparing with the case of its reference atom, giving rise to the generation of single attosecond pulses. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15648]  |
| 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 | 于永丽. 基于气体高次谐波的阿秒脉冲产生及控制理论研究[D]. 中国科学院上海光学精密机械研究所. 2010. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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