强场气体高次谐波的特性分析和实验研究
毕业论文关键词 高次谐波 Lewenstein量子理论模型 含时薛定谔方程 传播效应 阿秒脉冲
Title Characteristic analysis and experimental study of high-order harmonic generation in gases at high laser intensity Abstract High-order harmonic has a broad application prospect in generating soft X-ray and attosecond sources because of its excellent characteristics in frequency domain. In this thesis, we use Lewenstein quantum model and TDSE method to generate high-order harmonics. By computation and analyzing, we found that except for a quantitative difference, the structure of the exact harmonic spectrum is excellently reproduced by the Lewenstein model for high photon energies near the cutoff. Study indicates that ionization energy of the gas and parameters of the laser pulse like wavelength, pulse intensity, pulse width and pulse shape all affect the harmonics generation. We did the calculation and analysis of harmonic spectrum under these conditions. Besides, we studied propagation effect of harmonics generated by Lewenstein model and plotted space distribution of electric field of different order harmonics in the plane right after the gas target and in a far-away plane. The super continuum generated by a few-cycle laser pulse has also been investigated and used to synthesize an isolated broadband 221-attosecond pulse. At last, we conducted a simple experiment to generate high-order harmonics and did analysis of the result.
Keywords high-order harmonics Lewenstein model TDSE propagation effect attosecond pulse
目次
1绪论...1
1.1激光的发展历史..1
1.2激光与原子相互作用机制..2
1.3高次谐波的研究意义和进展2
2LEWENSTEIN量子理论描述高次谐波.8
2.1理论模型与编程实现..8
2.2单原子响应仿真结果.10
3数值求解薛定谔方程（TDSE）解释高次谐波19
3.1理论模型...19
3.2劈裂算符法(SPLIT-OPERATOR)解含时薛定谔方程...20
3.3最佳参数探索...22
3.4计算与讨论.24
4LEWENSTEIN与TDSE方法对比分析33
5高次谐波传播效应的研究34
5.1传播效应理论分析...34
5.2仿真结果...35
6高次谐波平台区产生阿秒脉冲37
6.1周期量级脉冲产生单个阿秒脉冲理论...37
6.2在LEWENSTEIN量子理论的基础上产生阿秒脉冲37
7气体高次谐波实验..41
7.1实验框架图.41
7.2实验设备...41
7.3实验结果...44
结论...46
致谢...47
参考文献..48
附录A原子单位和国际单位的转换...50
1 绪论 自从1960年第一台激光器诞生于实验室后[1]，激光技术已经越来越多地应用在人们生产生活的各个领域：激光读取光盘、激光医疗手术、激光全息等大大方便了人们的生活；激光微加工、激光非接触测量、激光控制和追踪化学反应也促进了工业的发展。近年来超快光学的进步促进了超强光脉冲的发展，产生的强大电场可以将电子从束缚原子态激发到远远大于库伦势的外电场中， 其电离率可与光学频率相比拟， 产生了许多传统理论无法解释的现象 （比如高次谐波产生） ，大大拓宽了非线性光学和强场物理的前沿。 本章将从激光的发展、激光与原子的相互作用机制、高次谐波的研究意义和进展等几个方面展开论述。