原子在强激光场中的电离
发布时间：2019-06-24 17:45
【摘要】：随着超短超强激光技术的快速发展,激光与原子相互作用的研究引起了人们的广泛关注。人们观察到了高次谐波发射(HHG),阈上电离(ATI),非序列双电子电离(NSDI)等强场物理现象。由于原子在强激光场中的电离是一切后续物理过程的基础,因此对原子的电离研究具有重要意义。所以,我们从理论上分别研究了原子在强激光脉冲作用下的阈上电离过程和双电离过程。具体研究工作包括以下内容:第一,我们通过求解单电子原子的一维含时薛定谔方程研究ATI过程。我们研究了一维长程势和短程势对电离谱平台结构的影响。发现在相同入射激光强度下,长程势下电离谱呈现出清晰的双平台结构;而短程势下电离谱双平台强度差明显小于长程势下的双平台强度差。并且,随着入射激光强度的减小,短程势下双平台结构逐渐变成单平台结构。我们通过量子模拟和经典分析,阐明了不同模型势下平台结构出现差异的原因:在相同入射激光强度下,短程势下电子电离几率小于长程势下的电离几率;在相同电离几率情况下,短程势的重散射截面大于长程势的重散射截面。第二,我们利用动量空间含时伪谱方法求解单电子原子的三维含时薛定谔方程研究ATI过程。首先研究了高频激光脉冲与激发态原子相互作用的光电离过程。通过计算电离阈值附近光电子能谱和动量角分布谱,发现体系初态波函数的主量子数可以由光电子能谱的第一个峰值位置来确定,体系初态波函数的角量子数可以由光电子动量角分布谱来确定。我们通过变化激光参数,发现这一规律不随入射激光强度和脉宽的改变而改变。因此我们可以利用高频激光脉冲中原子的电离信号对原子初态波函数进行标定。我们的方法为研究原子初态波函数成像问题提供了一种新方案。其次我们讨论了不同入射激光强度下的光电子谱,发现随入射激光强度的增加每个ATI峰由单峰变为多峰,如果继续增加入射激光强度,每个ATI峰再次变为单峰结构。上述计算结果与相应的实验测量结果符合很好。通过对原子束缚态布居分析,我们发现束缚态多光子激发导致上述现象的发生。最后我们讨论了在Freeman共振条件下,光电子能谱和光电子角分布与入射激光强度和激光脉冲的载波包络相位(CEP)的依赖关系。我们发现从基态直接电离的电子,ATI峰值位置随入射激光脉冲强度的增加移动一个pU(pU为有质动力能),从较高激发态电离的电子,ATI峰值位置随入射激光脉冲强度的增加不移动。原因如下:从基态直接电离的电子,由于基态具有较大的电离势,能级移动较小,而末态能级移动pU,所以ATI峰值位置随激光脉冲强度的增加而移动。而从较高激发态电离的电子,初态和末态能级在激光场作用下移动相同的pU,因此ATI峰值位置不会随着激光脉冲强度的增加而移动。此外,我们研究激光脉冲的CEP对光电子能谱的影响。发现在光电子能谱Freeman共振位置附近,光电子的电离几率随激光脉冲的CEP改变而改变。通过分析每个分波对光电子谱的贡献,我们可以确定影响光电子谱强度的分波。通过利用光电子角分布信息,我们能提供一种探测多周期激光脉冲CEP的新方案。第三,我们基于B样条理论求解双电子原子满足的含时薛定谔方程,研究了氦原子在深紫外(XUV)激光脉冲作用下的双光子双电离过程。首先我们检验计算方法在强XUV激光脉冲作用下的有效性。其次研究了激光脉冲宽度对电离电子能谱结构的影响。发现能量谱结构随脉冲宽度的增加由单峰变成双峰。通过对长脉冲下双电子电离动力学过程的分析,我们发现双电子在电离过程中的相互作用形成双峰结构。最后我们讨论了氦原子激发态1S2S和1S2P态作为初态时的电离过程。
[Abstract]:With the rapid development of the ultra-short and super-intense laser technology, the study of the interaction of the laser and the atoms has attracted a wide range of attention. The physical phenomena of high-order harmonic emission (HHG), suprathreshold ionization (ATI) and non-sequence double electron ionization (NSDI) were observed. The ionization of atoms in the strong laser field is the basis of all follow-up physical processes, so it is of great significance to study the ionization of atoms. So, we theoretically study the ionization process and the double ionization process of the atoms under the action of strong laser pulse. The specific research work includes the following: first, we study the ATI process by solving the one-dimensional time-time Schrodinger equation of the single electron atom. We have studied the effect of one-dimensional long-range potential and short-range potential on the structure of the platform. It is found that under the same incident laser intensity, a clear double-platform structure is displayed under the long-range potential, and the strength difference of the double-platform under the short-range potential is obviously smaller than that of the double-platform under the long-range potential. Moreover, with the decrease of the incident laser intensity, the double-platform structure gradually becomes a single-platform structure under the short-range potential. Through the quantum simulation and the classical analysis, the reason of the difference of the platform structure under the different model potential is explained: under the same incident laser intensity, the electron ionization probability under the short-range potential is less than the ionization probability under the long-range potential; and in the case of the same ionization probability, The cross section of the short-range potential is larger than the heavy-scattering cross-section of the long-range potential. Secondly, we use the momentum space-time pseudospectral method to solve the three-dimensional time-time Schrodinger equation of the single electron atom to study the ATI process. The photoionization process of the interaction between the high-frequency laser pulse and the excited-state atom is studied. The main quantum number of the initial state wave function of the system can be determined by the first peak position of the photoelectron spectrum by calculating the photoelectron spectrum and the momentum angular distribution spectrum near the ionization threshold, and the angle quantum number of the initial state wave function of the system can be determined by the photoelectron momentum angular distribution spectrum. By changing the laser parameters, we find that this rule does not change with the change of the intensity of the incident laser and the pulse width. So we can use the ionization signal of the atom in the high-frequency laser pulse to calibrate the atomic initial state wave function. Our method provides a new scheme for studying the imaging of the first-state wave function of the atom. Second, we discussed the photoelectron spectrum of different incident laser intensity, and found that each ATI peak changed from single peak to multi-peak with the increase of incident laser intensity, and if the incident laser intensity was continued to increase, each ATI peak again became a unimodal structure. The results of the above calculation are in good agreement with the corresponding experimental results. By analyzing the bound state of the atom, we find that the bound-state multi-photon excitation leads to the above-mentioned phenomenon. Finally, we discuss the dependence of the photoelectron spectrum and the photoelectronic angular distribution on the carrier envelope phase (CEP) of the incident laser intensity and the laser pulse under the Freeman resonance condition. We find that the peak position of ATI moves with the increase of the intensity of the incident laser pulse with the increase of the intensity of the incident laser pulse, and the peak position of ATI does not move with the increase of the intensity of the incident laser pulse. The reason is as follows: the electrons that are directly ionized from the ground state, because the ground state has a large ionization potential, the energy level moves smaller, and the last energy level moves the pU, so the peak position of the ATI moves with the increase of the laser pulse intensity. And the electron, the initial state and the final state energy level ionized from the higher excited state move the same pU under the action of the laser field, so the peak position of the ATI does not move with the increase of the laser pulse intensity. In addition, we study the effect of the CEP of the laser pulse on the photoelectron spectroscopy. It was found that in the vicinity of the Freeman resonance position of the photoelectron spectroscopy, the probability of ionization of the photoelectrons changes with the change of the CEP of the laser pulse. By analyzing the contribution of each wave to the photoelectron spectrum, we can determine the distribution of the intensity of the photoelectron spectrum. By using the optoelectronic angular distribution information, we can provide a new scheme for detecting a multi-period laser pulse CEP. Thirdly, we study the two-photon double ionization process under the action of deep ultraviolet (XUV) laser pulse by using the B-spline theory to solve the time-dependent Schrodinger equation. First, we verify the effectiveness of the calculation method under the strong XUV laser pulse. Secondly, the effect of laser pulse width on the structure of ionization electron energy spectrum is studied. It was found that the energy spectrum structure changed from single peak to double peak with the increase of the pulse width. Through the analysis of the dynamic process of double electron ionization under long pulse, we find that the interaction of the two electrons in the ionization process forms a double-peak structure. Finally, we discuss the ionization process of the states of the excited states of the helium atom and the state of the 1S2P as the initial state.
【学位授予单位】：吉林大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O562
本文编号：2505244
[Abstract]:With the rapid development of the ultra-short and super-intense laser technology, the study of the interaction of the laser and the atoms has attracted a wide range of attention. The physical phenomena of high-order harmonic emission (HHG), suprathreshold ionization (ATI) and non-sequence double electron ionization (NSDI) were observed. The ionization of atoms in the strong laser field is the basis of all follow-up physical processes, so it is of great significance to study the ionization of atoms. So, we theoretically study the ionization process and the double ionization process of the atoms under the action of strong laser pulse. The specific research work includes the following: first, we study the ATI process by solving the one-dimensional time-time Schrodinger equation of the single electron atom. We have studied the effect of one-dimensional long-range potential and short-range potential on the structure of the platform. It is found that under the same incident laser intensity, a clear double-platform structure is displayed under the long-range potential, and the strength difference of the double-platform under the short-range potential is obviously smaller than that of the double-platform under the long-range potential. Moreover, with the decrease of the incident laser intensity, the double-platform structure gradually becomes a single-platform structure under the short-range potential. Through the quantum simulation and the classical analysis, the reason of the difference of the platform structure under the different model potential is explained: under the same incident laser intensity, the electron ionization probability under the short-range potential is less than the ionization probability under the long-range potential; and in the case of the same ionization probability, The cross section of the short-range potential is larger than the heavy-scattering cross-section of the long-range potential. Secondly, we use the momentum space-time pseudospectral method to solve the three-dimensional time-time Schrodinger equation of the single electron atom to study the ATI process. The photoionization process of the interaction between the high-frequency laser pulse and the excited-state atom is studied. The main quantum number of the initial state wave function of the system can be determined by the first peak position of the photoelectron spectrum by calculating the photoelectron spectrum and the momentum angular distribution spectrum near the ionization threshold, and the angle quantum number of the initial state wave function of the system can be determined by the photoelectron momentum angular distribution spectrum. By changing the laser parameters, we find that this rule does not change with the change of the intensity of the incident laser and the pulse width. So we can use the ionization signal of the atom in the high-frequency laser pulse to calibrate the atomic initial state wave function. Our method provides a new scheme for studying the imaging of the first-state wave function of the atom. Second, we discussed the photoelectron spectrum of different incident laser intensity, and found that each ATI peak changed from single peak to multi-peak with the increase of incident laser intensity, and if the incident laser intensity was continued to increase, each ATI peak again became a unimodal structure. The results of the above calculation are in good agreement with the corresponding experimental results. By analyzing the bound state of the atom, we find that the bound-state multi-photon excitation leads to the above-mentioned phenomenon. Finally, we discuss the dependence of the photoelectron spectrum and the photoelectronic angular distribution on the carrier envelope phase (CEP) of the incident laser intensity and the laser pulse under the Freeman resonance condition. We find that the peak position of ATI moves with the increase of the intensity of the incident laser pulse with the increase of the intensity of the incident laser pulse, and the peak position of ATI does not move with the increase of the intensity of the incident laser pulse. The reason is as follows: the electrons that are directly ionized from the ground state, because the ground state has a large ionization potential, the energy level moves smaller, and the last energy level moves the pU, so the peak position of the ATI moves with the increase of the laser pulse intensity. And the electron, the initial state and the final state energy level ionized from the higher excited state move the same pU under the action of the laser field, so the peak position of the ATI does not move with the increase of the laser pulse intensity. In addition, we study the effect of the CEP of the laser pulse on the photoelectron spectroscopy. It was found that in the vicinity of the Freeman resonance position of the photoelectron spectroscopy, the probability of ionization of the photoelectrons changes with the change of the CEP of the laser pulse. By analyzing the contribution of each wave to the photoelectron spectrum, we can determine the distribution of the intensity of the photoelectron spectrum. By using the optoelectronic angular distribution information, we can provide a new scheme for detecting a multi-period laser pulse CEP. Thirdly, we study the two-photon double ionization process under the action of deep ultraviolet (XUV) laser pulse by using the B-spline theory to solve the time-dependent Schrodinger equation. First, we verify the effectiveness of the calculation method under the strong XUV laser pulse. Secondly, the effect of laser pulse width on the structure of ionization electron energy spectrum is studied. It was found that the energy spectrum structure changed from single peak to double peak with the increase of the pulse width. Through the analysis of the dynamic process of double electron ionization under long pulse, we find that the interaction of the two electrons in the ionization process forms a double-peak structure. Finally, we discuss the ionization process of the states of the excited states of the helium atom and the state of the 1S2P as the initial state.
【学位授予单位】：吉林大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：O562
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