| 题名 | 超冷中性等离子体的DIH模拟与低能ATI的研究 |
| 作者 | 郭丽 |
| 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 | 韩申生 |
| 关键词 | 超冷中性等离子体 有序排布 强耦合 隧穿电离 动量谱和能量谱 时间-能量分布 S矩阵 |
| 其他题名 | The simulation of DIH in ultracold neutral plasmas and the study of low energy of ATI |
| 中文摘要 | 超冷中性等离子体是国际上近年来新兴的前沿研究领域，强场物理领域里的阈上电离（ATI）低能光电子运动特性也是一个有趣的前沿研究方向。这两个领域的研究具有重要的科学意义和潜在的应用价值，尤其为将来交叉研究起到铺垫作用。 本文主要对超冷中性等离子体中的热点问题以及对强场物理中两个先前理论不能解释的最新实验现象进行了深入研究。取得的主要创新研究成果如下： 1. 首次用不含截断近似的分子动力学程序对初始密度为有序光晶格排布的超冷中性等离子 体进行了模拟，模拟结果显示电子对离子的碰撞加热效应很重要，但只要实验初始参数选取 的恰当，离子达到强耦合是可能的。模拟发现，当初始密度为高斯分布时，结果重现了无序诱导加热效应（DIH）和离子动能振荡，这也验证了程序的可靠性。为了避免DIH，使离子达到强耦合状态，进一步对初始有序排布的超冷等离子体进行了模拟，模拟结果却发现电子对离子的碰撞加热很重要。进一步还发现，在初始有序光晶格排布的单离子成分的超冷等离子体的模拟中出现了有序冷却现象。 2. 首次在S矩阵展开式第二项中考虑了电子与离子的长程库仑作用，并用它计算了平行于偏振方向的动量分布。研究发现，仅用S矩阵展开式的第一项计算，在考虑真实的实验条件后，理论结果不能重现出实验结构。对S矩阵详细研究之后，我们对矩阵中长程库仑势引起的发散进行了类似重整化的处理。当仅用S矩阵展开式的第二项时，理论结果展现出双峰结构并且峰的位置不随强度变化而移动，这些结果与实验数据定性的符合。通过进一步分析，发现双峰结构是离子对电子的长程库仑吸引造成的。 3. 基于以上结论，用包含长程库仑势的S矩阵展开式的第二项计算了平行于偏振方向的电子低能谱，理论结果重现出了实验上的两个峰。进一步分析了两峰产生的原因：第一个峰是由于电子与离子弹性碰撞并且大角度散射造成的；第二个宽峰则是由电子与离子间弹性和非弹性碰撞中的前向散射造成的。 4. 首次给出并分析了电离后电子的时间-能量分布。根据跃迁几率公式的特点首先定义了类维格纳分布函数，然后用该函数给出了电离后电子的时间-能量分布，从该分布中可以更加清楚直观的看到ATI中的干涉峰，更具有说服力的证明AIT干涉峰是由脉冲的有限宽度引起的。 |
| 英文摘要 | Ultracold neutral plasma (UCP)is a frontier area arisen in recent years. Low energy electron dynamics of above-threshold ionization (ATI) in intense field physics is also an interesting front subject. The studies for these two fields have great academic significance and potential application, and especially pave the way to the cross discipline research. In this dissertation, a detail study is performed about a hot point in UCP and two new experimental phenomena of intense field physics, which can not be explained by the previous theory. The main innovative results are as follows: 1. We simulate UCP with the ordered initial lattice distribution by using molecular dynamics program which does not contain the truncation calculation. The simulation results show electron collisional heating for ions is important in this simulation. However, carefully prepared the initial condition, a strongly coupled UCP can be realized. For Gaussian initial distribution for atoms, the simulation results reproduce disorder-induced heating (DIH) and kinetic energy oscillations, which verify the correctness of the program. In order to avoid DIH and keep ions still in a strong coupling, the simulations for UCP with ordered lattice initial density distribution are performed. The results show that collisional heating from electrons is important for UCP with the ordered lattice distribution. Further, the order-induced cooling is observed for one-component plasma with an ordered lattice initial distribution. 2. The long-range Coulomb interaction between electron and ion is firstly considered in the second term of the expansion of S-matrix and we use this term to calculate the distribution of electron momentum parallel to the polarization direction of laser field. Taking into account the first term of S-matrix and real experimental conditions, the theoretical results do not reproduced the experimental structure. A renormalization-like method is used to resolve the long-range Coulomb divergence in S-matrix. When only considering the second term of S-matrix, the obtained results display the double-hump structures and the peak positions are independent of the intensity, which are qualitatively consistent with the experimental data. Further, we find that double-hump structure is attributed to the long-range Coulomb attraction from the ion. 3. Based on the above conclusion, low-energy electron spectrum in the polarization direction of the laser field is investigated by using the second term of S-matrix including the long-range potential. The theoretical results reproduce the two peaks observed in the experiment, which are not displayed in the calculations from the first term of S-matrix. Further analysis of the reasons for the two peaks: the first peak is due to elastic collisions and large angle scattering between electron and ion; the second peak is ascribed to the electron that experiences elastic and inelastic forward scattering when it interacts with the ion. 4. Time-energy distribution of photoelectron emitted from an atom in intense laser field is firstly present and analyzed. Based on the characteristic of transition probability formula, we propose a Wigner-distribution-like function to analyze the time-energy distribution of electron spectrum. This method enables us to give a convincing and complete explanation for the interference effects in ATI peaks due to the finite pulse duration. |
| 语种 | 中文 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15644]  |
| 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 | 郭丽. 超冷中性等离子体的DIH模拟与低能ATI的研究[D]. 中国科学院上海光学精密机械研究所. 2010. |
| 个性服务 |
| 查看访问统计 |
| 相关权益政策 |
| 暂无数据 |
| 收藏/分享 |
除非特别说明，本系统中所有内容都受版权保护，并保留所有权利。
修改评论