取向分子高次谐波辐射效率与驱动激光波长关系的理论研究

发布时间：2018-03-14 01:03

本文选题：谐波效率　切入点：分子结构　出处：《陕西师范大学》2015年硕士论文　论文类型：学位论文

【摘要】：强激光场中物质的高次谐波辐射是当前强场物理领域关注的热点问题之一。首先,利用谐波辐射可以得到阿秒脉冲,后者在科学技术中有广泛的应用。另外,利用谐波辐射可以在超快时间尺度内实现分子的轨道成像,这对理解化学反应具有重要的意义。从实际应用的角度考虑,人们除了希望充分拓展谐波平台,进而得到更短的阿秒脉冲外,人们还希望在更低的驱动激光场输入功率下得到更高的谐波辐射产量,进而得到更强的阿秒脉冲。因此提高谐波辐射效率(谐波积分产量与驱动激光场功率之比)的方法也一直为人们所关注。近年来,人们已经深入研究了谐波辐射效率与驱动激光场波长的关系。在实验测量方面,实验结果表明谐波效率随波长变化的标度律为λ-(6.3±1.1)；在数值模拟方面,通过求解含时薛定谔方程给出的标度律为λ-(5-6),与实验结果符合得较好；在理论研究方面,通过强场近似(SFA：strong-field approximation)方法给出的标度律与前两者不完全相符。目前对谐波辐射效率的研究主要集中在原子。对分子谐波辐射效率的研究较少。对于分子而言,由于其具有更多的自由度和多中心特征,其在强激光场中的动力学也更加复杂,展示了许多新的效应(例如取向效应,两中心干涉效应等)。本文我们将详细研究分子谐波辐射效率与分子取向,驱动激光波长之间的关系。本文第三章研究了在不同激光波长(400nm到2300nm)下,取向分子H2+产生的高次谐波。数值的模拟结果表明波长依赖的高次谐波效率与分子取向密切相关。我们的分析揭示出对于不同的波长所产生高次谐波,再散射电子的动力学性质扮演了举足轻重的角色。在这个过程中,电子的动力学与分子结构之间的相互作用起到主导性作用。本章给出一个简单的模型来描述波长取向依赖的高次谐波产生现象,并展示了取向分子在不同电子路径下产生谐波效率的波长标度。本文第四章通过数值计算,研究了强激光场中CO2分子在不同波长和取向角下产生的高次谐波辐射的效率。我们的研究表明,CO2分子的垂直谐波效率在较小的和中间的取向角时倾向于与平行谐波效率可比或更高,而在较大的取向角时,垂直谐波效率远低于平行谐波效率。进一步的分析表明CO2分子的结构对其垂直谐波效率有重要的影响,且该影响与波长有关。本章的研究建议对于较复杂的分子,应该在分子的轨道成像实验中考虑垂直谐波的贡献。
[Abstract]:The high order harmonic radiation of matter in the intense laser field is one of the hot issues in the field of strong field physics. Firstly, the attosecond pulse can be obtained by using the harmonic radiation, which is widely used in science and technology. The orbital imaging of molecules can be realized in ultrafast time scale by using harmonic radiation, which is of great significance for understanding chemical reactions. From the point of view of practical application, people want to fully expand the harmonic platform. In addition to the shorter attosecond pulse, people also hope to get higher harmonic radiation output at lower input power of the driving laser field. Therefore, the method of improving the harmonic radiation efficiency (the ratio of harmonic integral output to the power of driving laser field) has been paid more and more attention in recent years. The relationship between the harmonic radiation efficiency and the wavelength of the driving laser field has been deeply studied. The experimental results show that the scaling law of the variation of harmonic efficiency with the wavelength is 位 -6. 3 卤1.1, and in the aspect of numerical simulation, The scalar law given by solving the time-dependent Schrodinger equation is 位 -N 5-6, which is in good agreement with the experimental results. The scaling law given by the strong field approximation (SFA): strong-field approximation method is not completely consistent with the former two methods. At present, the research on harmonic radiation efficiency is mainly focused on atoms, but less on molecular harmonic radiation efficiency. Because of its more degree of freedom and multi-center characteristics, its dynamics in the intense laser field is more complex, showing many new effects (such as orientation effect). In this paper, we will study in detail the relationship between the efficiency of molecular harmonic radiation and the molecular orientation and the driving wavelength of the laser. In the third chapter, we study the effects of different laser wavelengths from 400 nm to 2300 nm. Numerical simulation results show that the wavelength dependent high harmonic efficiency is closely related to the molecular orientation. Our analysis reveals that high order harmonics are generated for different wavelengths. The dynamical properties of the rescattered electrons play an important role. The interaction between electron dynamics and molecular structure plays a dominant role. In this chapter, a simple model is given to describe the phenomenon of wavelength orientation-dependent high-order harmonic generation. The wavelength scaling of harmonic efficiency of oriented molecules under different electron paths is also shown. Chapter 4th is numerically calculated. The high order harmonic radiation efficiency of CO2 molecules at different wavelengths and orientation angles in a high intensity laser field is studied. Our results show that the vertical harmonic efficiency of CO 2 molecules tends to be parallel to that of parallel harmonics at small and intermediate orientation angles. Wave efficiency is comparable or higher, The vertical harmonic efficiency is much lower than the parallel harmonic efficiency when the orientation angle is large. Further analysis shows that the structure of CO2 molecule has an important influence on its vertical harmonic efficiency. In this chapter, it is suggested that the contribution of vertical harmonics should be taken into account in the orbital imaging experiments for more complex molecules.
【学位授予单位】：陕西师范大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN24

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