势函数对强激光场中电离的影响

发布时间：2018-04-04 10:24

本文选题：势函数　切入点：软核参数　出处：《吉林大学》2017年硕士论文

【摘要】：随着激光技术的发展,激光对原子、分子内部电子的作用已经达到甚至超过电子所感受的库仑作用。电子在如此强的激光电场作用下,原子、分子中的电子会在很短的时间获得足够的能量摆脱母体离子的束缚发生电离。强场原子、分子相互作用产生的阈上电离,非序列电离等过程已成为人们关注的重点。理论研究在电离过程中,通常选择一个势函数来描述电子与核以及其他电子的相互作用。本论文通过全经典方案研究不同势函数参数以及不同分子准直条件下的光电子发射谱,分析势函数在电离和重碰过程中的作用。具体研究包括以下三方面内容:一、分析了原子势函数中不同软核参数对光电子发射谱的影响。研究发现,在相同线偏振入射激光脉冲作用下,随着原子软核参数数值的增加,光电子发射谱的较大横向(垂直于激光偏振方向)动量成分逐渐增加。通过对粒子轨迹的分析发现,光电子谱中横向动量接近于零的粒子主要来源是直接电离的电子。而光电子谱中横向动量较大的粒子主要来源于重散射电子。由于软核势参数较大时粒子有更集中的初始动量分布,这部分电离电子返回母体离子时,在库仑势函数的作用下获得横向动量,因而其光电子发射谱中较大横向动量所占成分更大。二、分析了入射激光偏振方向和分子轴之间夹角不同时分子离子的光电子发射谱。研究发现,当激光偏振方向和分子轴平行时,光电子发射谱在垂直于激光偏振方向呈对称分布,随着入射激光偏振方向和分子轴夹角的逐渐增加,其光电子分布呈现非对称特征。光电子主要分布在分子轴方向和激光偏振方向。通过对电离电子轨迹的分析发现,产生这种光电子分布的原因是由于电离电子返回到母体离子时,受到分子离子中两个核的共同作用,使电子产生非对称动量分布。三、分析了在电离增强核间距条件下氢分子的电子关联谱随着入射激光偏振方向与分子轴夹角的变化。研究发现,随着二者夹角的增加,电子关联谱从四个象限均匀分布逐渐向一、三象限过度。通过对电子轨迹分析发现,当激光场偏振方向和分子轴平行时,序列电离过程起主要作用,第二个电子在第一个电子电离后的多个周期内均有电离发生。第一个电子电离时,第二个电子获得能量发生共振激发,电子运动范围变大,在之后的激光电场峰值附近发生电离。在入射激光偏振和分子轴垂直时,非序列电离过程起主要作用,电离主要发生在第一个电子电离过程后的一个周期内。
[Abstract]:With the development of laser technology, the effect of laser on electrons in atoms and molecules has reached or exceeded the Coulomb effect of electrons.The electrons in atoms and molecules under such a strong laser electric field will gain enough energy to get rid of the binding of the parent ions to ionization in a very short time.The processes of suprathreshold ionization and nonsequential ionization due to the interaction of strong field atoms and molecules have become the focus of attention.In the process of ionization, a potential function is usually chosen to describe the interaction of electrons with nuclei and other electrons.In this paper, the photoemission spectra of different potential function parameters and different molecular collimation conditions are studied by means of the whole classical scheme, and the function of potential function in the process of ionization and recollision is analyzed.The research includes the following three aspects: firstly, the influence of different soft core parameters in atomic potential function on the photoelectron emission spectrum is analyzed.It is found that under the action of the same linearly polarized incident laser pulse, the larger transverse (perpendicular to the laser polarization direction) momentum component of the photoelectron emission spectra increases with the increase of the atomic soft core parameters.Through the analysis of the particle trajectories, it is found that the main source of the particles in the photoelectron spectrum is the directly ionized electrons that the transverse momentum is close to zero.The particles with large transverse momentum in the photoelectron spectrum are mainly derived from the heavy scattering electrons.Because the particle has a more concentrated initial momentum distribution when the soft core potential parameter is larger, when the partial ionized electron returns to the parent ion, the transverse momentum is obtained under the action of the Coulomb potential function.Therefore, the larger transverse momentum in the photoelectron emission spectrum is larger.Second, the photoelectron emission spectra of molecular ions at different angles between the polarization direction and the molecular axis of the incident laser are analyzed.It is found that when the polarization direction of the laser is parallel to the molecular axis, the photoelectron emission spectrum is symmetrically distributed perpendicular to the polarization direction of the laser, and with the increasing of the polarization direction and the molecular axis angle of the incident laser,The photoelectron distribution is asymmetric.The photoelectron is mainly distributed in the direction of molecular axis and laser polarization.Through the analysis of the ionized electron trajectories, it is found that the photoelectron distribution is due to the asymmetric momentum distribution of the electrons when the ionization electrons return to the parent ions and are subjected to the interaction of the two nuclei in the molecular ions.Thirdly, the changes of electron correlation spectra of hydrogen molecules with the polarization direction of incident laser and the angle between the molecular axis and the polarization direction are analyzed under the condition of ionization enhanced nuclear spacing.It is found that with the increase of the angle between the two, the uniform distribution of electron correlation spectrum from four quadrants to one and three quadrants is gradually excessive.It is found that the sequence ionization process plays a major role when the polarization direction of the laser field is parallel to the molecular axis, and the second electron is ionized in several periods after the first electron ionization.When the first electron is ionized, the second electron gets resonance excitation, the range of electron motion becomes larger and ionization occurs near the peak of the laser electric field.When the incident laser is polarized and the molecular axis is perpendicular, the nonsequential ionization process plays a major role, and ionization mainly occurs in a period after the first electron ionization process.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O56

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