飞秒激光诱导一氧化氮分子电离光电子速度成像研究
发布时间：2018-09-05 11:07
【摘要】：本论文以异核双原子分子一氧化氮为例,通过速度成像技术在实验上探测了飞秒强激光场与分子作用电离产生的光电子速度成像,分析了激光光强对其共振激发电离路径的影响,讨论了其内部的不同里德堡态在电离过程中的贡献,同时提取了相关里德堡态的角度分布特性信息。通过分析逸出电子的动能和角度分布信息,为进一步深入地理解分子的电离过程提供了实验依据。相对原子而言,分子的能级结构更为复杂,在分子的电离解离过程研究中仍有很多现象还未得到准确充分的解释。为解决这些问题不仅需要发展更接近分子实际情况的理论模型,在实验技术手段上也要不断的发展和创新。由此,本实验室搭建了六极杆装置和电子速度成像装置,分子束通过六极杆实现聚焦后与飞秒强激光场作用产生电子,再通过速度成像装置对电子进行速度成像探测。本文工作中提取并获得了一氧化氮分子电离光电子的动能分布及角度分布。在本论文的实验工作中对六极杆施加高压的主要目的是将分子束聚焦以获得更强的产物信号,实验中所使用的激光光源是线偏振800 nm和400 nm的飞秒激光,当波长锁定在800 nm时,测量得到了不同激光光强(从1.1×10~（13） W/cm~2到7.8×10~（13） W/cm~2范围内)的光电子速度成像,通过对光电子动能谱结构及其随光强的通道切换现象进行分析,将出现的共振峰全部进行了归属,确定了在不同的光强作用下参与电离的里德堡态,同时还获得了电离过程中各里德堡态的逸出电子角度分布信息。当激光波长为400 nm时,测得了激光光强从2.0×10~（12）W/cm~2到1.4×10~（13）W/cm~2范围内的不同光强下光电子速度成像。与800 nm的光电子动能谱不同,400 nm下的能谱结构较单一,只存在一个较为清晰的共振峰及其对应的ATI结构。我们将800 nm出现的通道切换现象归结为激光外场引起一氧化氮分子内电子激发态能级的斯塔克移动,即随着激光光强的改变在电离过程中共振电子激发态的贡献也会发生变化,某特定电子激发态由于斯塔克效应而正好步入多光子共振区,导致动能谱中对应的峰值信号增强;同时部分电子激发态则由于斯塔克移动而逐渐远离多光子共振区,所以对应的峰值信号发生相应减弱。进一步通过对比不同激光光强下共振电离过程中各里德堡态所对应的电子角度分布,我们发现电离光电子角度分布基本体现的是里德堡态的本质属性。一氧化氮分子光电子成像的实验探测研究,有助于我们对分子内部里德堡态的结构建立更全面的认识,更深入的理解一氧化氮分子的飞秒激光诱导共振增强多光子电离过程及过程中明显的通道切换现象和电子角度分布,本论文工作中关于激光光强对分子电子激发态影响的分析,为实现强场下分子过程的量子调控提供了实验数据及相关依据。
[Abstract]:Taking the heteronuclear diatomic molecule nitric oxide as an example, the photoelectron velocity imaging produced by intense femtosecond laser field and molecular ionization is experimentally detected by velocity imaging technique in this thesis. The influence of laser intensity on the resonance excited ionization path is analyzed. The contribution of different Rydberg states in the process of ionization is discussed. The angular distribution characteristics of the related Rydberg states are also extracted. By analyzing the kinetic energy and angular distribution information of the escaping electrons, this paper provides an experimental basis for further understanding the ionization process of molecules. Compared with atoms, the energy level structure of molecules is more complex, and there are still many phenomena in the process of molecular ionization and dissociation that have not been fully explained. In order to solve these problems, it is necessary not only to develop theoretical models which are closer to the actual conditions of molecules, but also to develop and innovate the experimental techniques. Thus, a six-pole device and an electronic velocity imaging device are built in our laboratory. The molecular beam is focused through the six-pole rod to produce electrons after focusing with the femtosecond intense laser field, and then the velocity imaging device is used to detect the velocity of the electrons. The kinetic energy distribution and angular distribution of ionization photoelectron of nitric oxide have been obtained. The main purpose of applying high pressure to the hexpole rod in this paper is to focus the molecular beam to obtain a stronger product signal. The laser source used in the experiment is linearly polarized femtosecond laser of 800 nm and 400 nm, when the wavelength is locked at 800 nm. The photoelectron velocity imaging of different laser intensities (from 1.1 脳 10 ~ (13) W/cm~2 to 7.8 脳 10 ~ (13) W/cm~2) has been obtained. By analyzing the structure of the photoelectron kinetic energy spectrum and its channel switching with the light intensity, all the resonance peaks have been assigned. The Rydberg states which take part in ionization under different light intensities are determined, and the angle distribution information of the escape electrons of each Rydberg state in the process of ionization is also obtained. When the laser wavelength is 400 nm, the photoelectron velocities in the range from 2.0 脳 10 ~ (12) W/cm~2 to 1.4 脳 10 ~ (13) W/cm~2 have been measured. In contrast to the photoelectron kinetic energy spectrum of 800 nm, the spectral structure at 400 nm is relatively simple, and there is only one clear resonance peak and its corresponding ATI structure. The phenomenon of channel switching in 800 nm is attributed to the Stark shift of the excited state of the electron in the nitric oxide molecule caused by the external field of the laser, that is, the contribution of the resonant electron excited state to the ionization process will also change with the change of the intensity of the laser light. Due to the Stark effect, a certain excited state enters the multi-photon resonance region, which leads to the enhancement of the corresponding peak signal in the kinetic energy spectrum, while the partial excited state is gradually away from the multi-photon resonance region because of the Stark shift. So the corresponding peak signal weakens accordingly. Furthermore, by comparing the electron angular distributions of each Rydberg state in the process of resonance ionization under different laser intensities, we find that the angular distribution of ionization photoelectrons basically reflects the essential properties of the Rydberg state. The experimental investigation of nitric oxide photoelectron imaging will help us to establish a more comprehensive understanding of the structure of the Rydberg state within the molecule. A deeper understanding of the femtosecond laser-induced resonance enhanced multiphoton ionization process of nitric oxide and the obvious channel switching and electron angle distribution in the process is presented. In this work, the effect of laser intensity on the excited states of molecular electrons is analyzed. It provides experimental data and relevant basis for realizing quantum regulation of molecular process in strong field.
【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】：O561
本文编号：2224085
[Abstract]:Taking the heteronuclear diatomic molecule nitric oxide as an example, the photoelectron velocity imaging produced by intense femtosecond laser field and molecular ionization is experimentally detected by velocity imaging technique in this thesis. The influence of laser intensity on the resonance excited ionization path is analyzed. The contribution of different Rydberg states in the process of ionization is discussed. The angular distribution characteristics of the related Rydberg states are also extracted. By analyzing the kinetic energy and angular distribution information of the escaping electrons, this paper provides an experimental basis for further understanding the ionization process of molecules. Compared with atoms, the energy level structure of molecules is more complex, and there are still many phenomena in the process of molecular ionization and dissociation that have not been fully explained. In order to solve these problems, it is necessary not only to develop theoretical models which are closer to the actual conditions of molecules, but also to develop and innovate the experimental techniques. Thus, a six-pole device and an electronic velocity imaging device are built in our laboratory. The molecular beam is focused through the six-pole rod to produce electrons after focusing with the femtosecond intense laser field, and then the velocity imaging device is used to detect the velocity of the electrons. The kinetic energy distribution and angular distribution of ionization photoelectron of nitric oxide have been obtained. The main purpose of applying high pressure to the hexpole rod in this paper is to focus the molecular beam to obtain a stronger product signal. The laser source used in the experiment is linearly polarized femtosecond laser of 800 nm and 400 nm, when the wavelength is locked at 800 nm. The photoelectron velocity imaging of different laser intensities (from 1.1 脳 10 ~ (13) W/cm~2 to 7.8 脳 10 ~ (13) W/cm~2) has been obtained. By analyzing the structure of the photoelectron kinetic energy spectrum and its channel switching with the light intensity, all the resonance peaks have been assigned. The Rydberg states which take part in ionization under different light intensities are determined, and the angle distribution information of the escape electrons of each Rydberg state in the process of ionization is also obtained. When the laser wavelength is 400 nm, the photoelectron velocities in the range from 2.0 脳 10 ~ (12) W/cm~2 to 1.4 脳 10 ~ (13) W/cm~2 have been measured. In contrast to the photoelectron kinetic energy spectrum of 800 nm, the spectral structure at 400 nm is relatively simple, and there is only one clear resonance peak and its corresponding ATI structure. The phenomenon of channel switching in 800 nm is attributed to the Stark shift of the excited state of the electron in the nitric oxide molecule caused by the external field of the laser, that is, the contribution of the resonant electron excited state to the ionization process will also change with the change of the intensity of the laser light. Due to the Stark effect, a certain excited state enters the multi-photon resonance region, which leads to the enhancement of the corresponding peak signal in the kinetic energy spectrum, while the partial excited state is gradually away from the multi-photon resonance region because of the Stark shift. So the corresponding peak signal weakens accordingly. Furthermore, by comparing the electron angular distributions of each Rydberg state in the process of resonance ionization under different laser intensities, we find that the angular distribution of ionization photoelectrons basically reflects the essential properties of the Rydberg state. The experimental investigation of nitric oxide photoelectron imaging will help us to establish a more comprehensive understanding of the structure of the Rydberg state within the molecule. A deeper understanding of the femtosecond laser-induced resonance enhanced multiphoton ionization process of nitric oxide and the obvious channel switching and electron angle distribution in the process is presented. In this work, the effect of laser intensity on the excited states of molecular electrons is analyzed. It provides experimental data and relevant basis for realizing quantum regulation of molecular process in strong field.
【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】：O561
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