| 题名 | 强光场中原子内壳层激射与团簇爆炸的超快动力学研究 |
| 作者 | 刘建胜 |
| 学位类别 | 博士 |
| 答辩日期 | 2003 |
| 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 | 超快X射线源 内壳层X射线激光 大尺寸团簇 超短超强激光 超快动力学诊断 |
| 其他题名 | Study on the Ultrafast Dynamics of Atomic Inner-Shell Lasing and Cluster Explosion in Strong Light Field |
| 中文摘要 | 自从1985年首次实现X射线激光以来，科学家们一直致力于追求更短波长的X射线激光和装置的小型化，并且取得了显著进展。然而传统的X射线激光机制（三体复合机制和电子碰撞激发机制）难以实现波长短于2nm的突破。随着超短超强激光技术的迅猛发展，目前在小型化台式激光系统上，已经实现了时间宽度小于10fs的超短脉冲激光，而在可聚焦功率密度方面也已经达到了-1020W／cm2量级。这种超快超强激光的出现带来许多潜在的应用：产生超快的X射线辐射、利用超快X射线辐射源泵浦原子内壳层产生极短波长的X射线激光、阿秒脉冲的产生、激光与团簇作用中极短波长的内壳层X射线辐射以及核聚变等。探索利用超快超强激光作为驱动源，在原子内壳层以及团簇中实现极短波长X射线激光将有可能克服传统机制难以突破波长短于2nm的障碍，成为发展超短波长相干辐射的极具潜力的新途径。本论文主要开展了超快X射线辐射源泵浦原子内壳层产生X射线激射的超快动力学过程以及团簇在强光场中爆炸的超快动力学研究。本论文取得的主要创造性成果如下：1．首先以碳原子为例，提出了五能级模型，采用超快X射线辐射泵浦源计算了碳原子内壳层光电离X射线激光在不同驱动激光条件下的瞬态增益系数。推导出了低Z元素内壳层光电离X射线激光增益系数随抽运速率的上升速率、原子浓度以及时间变化的解析模型，给出了峰值时间和峰值增益。利用该模型分析了碳、氮和氖原子产生内壳层X射线激光所需的激光条件和最佳参数的选取，并纠正了美国劳伦斯利弗莫尔国家实验室提出的物理方案中的计算错误。计算分析的结果表明，氖和氮比碳原子更有希望成为实现内壳层光电离X射线激光的候选介质。2．采用均匀的流体动力学模型分析了大尺寸团簇在超短脉冲激光场中的动力学过程。对于均匀的流体动力学模型，由于有共振吸收的存在，在共振吸收附近，由于电场的增强，使得线性近似下的极化屏蔽场并不能完全描述团簇在共振吸收处的物理过程。提出了有效介电常数模型，对团簇在共振吸收处的行为进行了弱化。利用该模型定性地分析了激光与团簇相互作用过程中体现的对激光脉宽、激光波长和团簇尺寸的依赖效应，与实验结果比较吻合。3.建立了包含多种粒子的非均匀球对称膨胀模型。利用该模型计算了大尺寸团簇中不同电荷态离子和电子随时间的运动过程，计算了离子的能谱分布和不同电荷态离子的平均能量。计算结果表明团簇膨胀呈现非均匀的流体膨胀特性，在膨胀的过程中，能够产生几百keV的高能离子，由于高电荷态离子受到较大的库仑力得到更加有效的加速而获得更高的动能。4．利用线性惆啾脉冲激光作为探针，设计并建立了一套超快动力学诊断测量系统。在理论上分析了利用线性惆啾脉冲激光对吸收进行直接测量的时间分辨率以及频谱干涉测量技术中相位重构的方法和时间分辨率。5．首次对超强超快激光与团簇相互作用过程中原子的电离过程、团簇的膨胀、以及探测光的损耗进行了时间分辨的测量。在脉宽250-30Ofs，功率密度3-5×1015W／cm2的激光与Ar，Kr，Xe团簇相互作用过程中利用碉啾频谱干涉仪测量的结果显示激光与团簇作用过程中产生了高价离子，离子价态分别为-Ars＋，～Kr12＋，～Xe17＋，表明激光与团簇有强烈的藕合作用。团簇等离子体对探测光有很强的吸收，探测光的损耗起始于原子电离的前沿，相移变化的时间尺度反映了团簇膨胀、离子电离过程的时间尺度。从高价离子的产生以及相移变化的时间尺度来看，团簇在激光场中的离化过程与气体原子的离化过程有很大的差异。 |
| 英文摘要 | Since the first demonstration of x-ray lasing in 1985, scientists have been committing themselves to seek after the utilization of shorter-wavelength x-ray lasers on a smaller system, and good progress has been made. However, the realization of x-ray lasing with ultrashort wavelength of less than 2nm was found rather difficult with the traditional schemes. With the tremendous progress in laser technology, laser pulses with a duration of shorter than lOfs and laser intensity on the 1020W/cm2 scale have been available on a compact table-top system. Potential applications of these ultrafast high-intensity lasers include the generation of ultrafast x-ray radiation, inner-shell photoionization x-ray lasers excited by ultrafast x-ray source, attosecond pulses, nuclear fusion and x-ray radiation with ultrashort wavelength from the inner-shell transition in the laser-cluster interactions. It constitutes an attractive new way to search after the utilization of x-ray lasing with ultrashort wavelength (<2nm) in atomic inner-shell and clusters by employing ultrafast high-intensity lasers. In this dissertation, the ultrafast dynamics of inner-shell photoionization x-ray lasing excited by ultrafast x-ray sources and the ultrafast explosion dynamics of clusters in strong light field have been investigated, the main results are given as follows: I. A model employing five-energy levels is proposed for the case of carbon to analyze the transient gain coefficient of inner-shell photoionization (ISPI) x-ray lasers excited by driving laser with different laser parameters. An analytical model has been deduced for low Z elements to analyze the time-varying gain coefficient vs. the density of lasing medium and the increase rate of pumping rate, and the time of the onset of the peak gain and its peak value have been given. Also the requirements on the intensity of the driving ultrashort pulse laser can be estimated, and the calculation mistake in LLNL's experimental scheme has been clarified. Employing this model, the gain for nitrogen and neon ISPI x-ray lasing has also been analyzed, and neon and nitrogen are more promising candidates for experimentally implementing ISPI x-ray lasers. The uniform hydrodynamic model has been employed to investigate the dynamics of large-size clusters under ultrashort high-intensity lasers. For this model, in the vicinity of resonance absorption, owing to the resonance enhancement of electric field, the polarized electric field under the linear assumption is unable to describe the process of resonance absorption. An effective dielectric constant was proposed to weaken the behavior of resonance absorption, and the interaction between different-size atomic cluster & and high-intensity laser pulses with different pulse durations and wavelengths has been qualitatively investigated to be approximately in agreement with experiment results. A nonuniform spherically symmetrical expansion model including different charged ions and electrons has been proposed to simulate the expanding process of large-size clusters in the laser-cluster interaction. The total ion energy spectrum, and average kinetic energy of different charged ions have been calculated. It is shown that the cluster exhibits a nonuniform expansion process and the ions with higher charge state possess much higher kinetic energy of up to several 100 keV. Using a linearly chirped pulse laser as a probe, a measurement system for ultrafast dynamics has been designed. The time resolution of direct absorption measurement using a linearly chirped laser pulse, and the methods of phase reconstruction and the time resolution of chirped spectral interferometry have been analyzed theoretically. Time-resolved measurement of ionization and explosion process of clusters and the depletion of the probe laser in the laser-cluster interactions have been investigated by employing a linearly chirped spectral interferometry. In the interactions of Ar, Kr, Xe clusters with lasers of 250-300fs, 3-5 X 1015W/cm2, the production of highly charged -Ar8+, -Kr12+and -Xe17+ions indicated a strong energy coupling between laser and clusters. Ultrafast depletion of the probe laser has been observed to be strictly coincident with the ionization front. The time scale of variation of phase shift reflects the clusters' explosion process, and the ionization dynamics of clusters is very different that of atoms. |
| 语种 | 中文 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15569]  |
| 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 | 刘建胜. 强光场中原子内壳层激射与团簇爆炸的超快动力学研究[D]. 中国科学院上海光学精密机械研究所. 2003. |
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