附加稳恒磁场对高次谐波产生过程的影响
时间:2020-06-21 15:32 来源:毕业论文 作者:毕业论文 点击:次
| 摘要本文选取附加稳恒磁场与强激光场联合作用下高次谐波的产生过程为研究对象，探索不同强度的附加稳恒磁场对谐波产生效率、截断位置等的影响。我们采用拟谱分裂算符方法，求解含时薛定谔方程；通过对含时电偶极矩的傅里叶变换获得高次谐波谱。我们的计算结果表明：附加磁场较弱时(0.01a.u.)，磁场对谐波产生过程的影响可以忽略不计；随着磁感应强度的增加(B=0.05a.u.),谐波的截止频率出现较大范围的延展；进一步增强磁感应强度（B=0.10a.u.），能进一步延展谐波的截止频率，并且能增强谐波的强度；然而更强磁场（B=0.20a.u.）并不能进一步延展谐波的截止频率。我们分析了不同磁感应强度下，电子在原子基态的分布几率，从而将稳恒磁场对高次谐波产生过程的影响归结为两种因素：(1) 磁势垒抑制电子电离;(2) 洛伦兹力增加电子重俘获几率。在此基础上，我们解释了不同强度的附加磁场下的高次谐波谱。该论文有图12 幅，表1 个，参考文献20 篇关键字： 稳恒磁场 高次谐波 分裂算符51415 The effect of the additional static magnetic field onthe high-order harmonic generation process AbstractI n this paper, we study the high-order harmonic generation process in theexternal field composed by a strong laser field and an additional static magnetic field.The pseudo-spectral split-operator method is used to solve the time-dependentSchrodinger equation; and the high order harmonic spectra are obtained by the theFourier transform of the time-dependent electric dipole moment. Our numericalresults show that when the magnetic field is weak (B=0.01a.u.), its effect can beneglected; with the increase of the magnetic field intensity (B=0.05a.u.), theharmonic cut-off frequency show a significant extension; a further enhancement ofthe magnetic intensity (B=0.10a.u.), can induce not only a further extension of theharmonic spectrum, but also an enhancement of the harmonic intensity; however,when the magnetic field is even stronger (B=0.20a.u.), the cut-off frequency can notbe further extended. We analyzed the electron’s survival probability at the groundstate in the laser pulse, and attributed the effect of the static magnetic field to twofactors: (1) magnetic barrier which prevents the electron ionization; (2) Lorentz forcewhich increases the re-collision probability of the ionized electron. The high orderharmonic spectra for different magnetic induction intensities of the additionalmagnetic field can be well understood. Key words: static magnetic field high-order harmonic Split-operator method 目录 摘要Ⅰ AbstractⅡ 目录Ⅲ 图清单-Ⅳ 表清单-Ⅳ 1绪论-1 1.1在强激光下与物质作用的研究-1 1.2原子在激光场中的电离-2 1.2.1多光子电离和阈上电离3 1.2.2随穿电离和过势垒电离-4 1.3高次谐波谱5 1.3.1高次谐波发射理论解释6 1.3.2高次谐波问题的研究意义7 2理论基础-9 2.1原子在激光场中的含时薛定谔方程-9 2.2拟谱法求解定态薛定谔方程9 2.3分裂算符法对波函数的时间演化11 2.3.1分裂算符法12 2.3.2波函数的时间演化-12 3数值模拟结果与讨论18 3.1不加入稳恒磁场时的高次谐波-18 3.2加入不同磁场的高次谐波谱-20 3.3附加稳恒磁场对谐波强度的影响--23 4总结--25 参考文献-26
致谢--27 |