非绝热准直卤代甲烷分子的电离产额及其光电子成像研究

发布时间：2018-04-30 17:55

本文选题：飞秒激光 + 六极杆静电场　；参考：《吉林大学》2016年博士论文

【摘要】：论文以卤代甲烷分子为例,结合实验与理论研究了分子在六极静电场与飞秒激光场的共同作用下的准直行为,讨论了如何通过速度成像实验数据中直接提取出分子准直程度参数〈P_2(cosθ)〉二阶勒让德多项式的平均值)的实验方法以及理论依据,由此得到了清晰和系统的对于分子转动动力学机制的认识。利用制备的准直与反准直分子,通过离子电离产额测量与电子成像实验,从不同侧面深入研究了卤代甲烷分子在强激光场中的电离行为。多原子分子在飞秒强激光场中的电离过程由于其量子态复杂性和多粒子关联一直是强场物理领域中的研究热点,尤其是在当激光强度介于多光子电离区与隧穿电离区之间时,目前还有很多物理问题尚未得到明确的解释。分子的准直技术可以将实验室坐标系与分子坐标系联系起来,这使得在分子坐标系下的强场物理研究成为了可能,同时也要求新实验探测技术的发展。我们发展了一套静电六极杆结合速度成像探测的实验装置,通过六极杆转动态选择,这一实验技术利用静电场与分子偶极矩之间的斯塔克效应可以得到处于|1±1(?)〉转动量子态的对称陀螺卤代甲烷分子。态选择后的分子通过与一束800 nm、偏振方向垂直于飞行时间质谱装置中静电提取场的线偏飞秒激光发生相互作用而被非绝热准直,随后分子被可控制时间延迟的第二束飞秒同偏振方向的线偏激光探测。理论上我们模拟了处于|1±1(?)1〉转动态的碘甲烷分子在准直激光偏振矢量垂直于离子透镜静电场这种垂直几何情况下的转动波包结构。在仅使用振幅尺度因子一个变量的情况下,实验测量的离子信号的转动波包周期形状重现了理论模拟的结果。可以看出,在速度成像装置惯常使用的垂直几何条件下,当准直激光强度足够强时产生离子对应的牛顿球相比于纯柱对称性的偏差小到可以忽略。理论模拟得到的准直参数在转动波包周期中最大和最小值位置处都与速度成像实验结果中提取出的准直参数对应的很好。实验中这种激光诱导可控的准直程度的上下极限可以达到〈P_2(cosθ)〉=0.7和〈P_2(cosθ)〉=-0.1。本文工作中完成了ppt理论程序的编写与调试,通过与惰性气体kr和xe在激光强度从1013w/cm2到1015w/cm2范围内电离产额实验结果相比较,验证了该ppt理论程序的可靠性并且实现了对于光强的标定。在这个光强区间内xe的电离曲线与ppt理论模拟的结果符合的很好,简单化的势垒抑制电离模型得到的饱和光强与ppt理论所给出的结果一致。对于kr在激光强度相对较低时的电离,实验上观测到了共振放大多光子电离的贡献。利用获得的准直分子作为研究体系,在激光强度从1013w/cm2到1015w/cm2的范围内对准直、随机分布和反准直的碘甲烷和溴甲烷分子的电离依存产额进行测量,并将得到的结果与经过修正的ppt理论模拟结果相对比,详细分析观测到不同光强区间内homo和低层分子轨道对于电离过程的贡献。对于较低光强下随机分布的ch3br分子的电离产额,实验测量结果与ppt理论预测结果存在偏差,我们将这部分偏差归因于通过具有a1对称性的轨道电离的贡献,这部分的贡献可能来自于共振激发过程;当激光强度相对较高时,电离主要是通过垂直于分子轴分布的e轨道(homo)的贡献。碘甲烷分子的电离与ppt理论模拟结果符合的很好,其电离主要是通过e轨道(homo)发生。利用六极杆转动态选择技术与激光准直技术的结合的这种方法实现了对电离过程中的不同轨道对于电离产额的贡献,即homo轨道和低层分子轨道的贡献的探测。通过角度分辨光电子速度成像的实验方法对准直与反准直的碘甲烷分子的多光子电离电子进行了成像测量。通过光电子能谱随光强的变化对电子能谱中的不同峰进行了指认,在光强为9.6×1012 W/cm2下观测到准直与反准直分子的电子能谱中两个通道的分支比的不同,我们将其归因于有效电离势随分子空间排列方向改变而改变所导致的。
[Abstract]:Taking the halogenated methane as an example, this paper studies the collimation behavior of molecules under the interaction of six polar electrostatic field and femtosecond laser field combined with experiment and theory, and discusses how to directly extract the average value of the two order Legendre polynomial of the molecular collimation degree parameter "P_2 (COS theta)" by the velocity imaging experimental data. A clear and systematic understanding of the mechanism of the kinetic mechanism of molecular rotation is obtained. Using the prepared collimator and the anti collimator, the ionization behavior of the halogenated methane molecules in the strong laser field is studied from different sides by the ion ionization yield measurement and the electron imaging experiment. The ionization process in the field is a hot spot in the field of strong field physics because of its quantum state complexity and multi particle association. Especially when the laser intensity is between the multiphoton ionization region and the tunneling ionization region, there are still many physical problems that have not been clearly explained. It is associated with the molecular coordinate system, which makes the study of strong field physics in the molecular coordinate system possible, and also requires the development of new experimental detection technology. We have developed a set of experimental device for electrostatic six pole combined with velocity imaging detection, and the dynamic selection through the six pole transfer. This experimental technique uses the electrostatic field and the molecular dipole. The stac effect between the moments can be obtained by a symmetric gyro halogenated methane molecule at the |1 + 1 (?) rotation quantum state. The molecule after selection is used by a linear femtosecond laser with a beam of 800 nm, the direction of polarization perpendicular to the time of the time of flight mass spectrometry, and is nonadiabatic collimation, and then the molecules are controlled. The line biased laser detection of second beams of delay in the same polarization direction. Theoretically we simulated the rotational wave packet structure of the iodide molecule at the |1 + 1 (?) 1 (?) 1 rotation in the vertical geometry of the collimated laser polarization vector perpendicular to the ion lens electrostatic field. The results of the theoretical simulation are reproduced by the rotational wave packet cycle shape of the measured ion signal. It can be seen that under the usual vertical geometric condition used in the velocity imaging device, the deviation of the ion corresponding to the Yu Chunzhu symmetry is negligible when the collimation laser is strong enough. The collimation parameter obtained by the theoretical simulation is obtained. The maximum and minimum positions in the rotational wave packet cycle correspond well with the collimation parameters extracted from the experimental results of the velocity imaging. In the experiment, the upper and lower limits of the controllable collimation degree of this laser can reach "P_2 (COS [theta) =0.7 and" P_2 (COS theta) =-0.1.. The writing of the PPT theory program has been completed and the writing of the PPT theory is completed. The test results are compared with the experimental results of the ionization yield of the inert gas Kr and Xe at the laser intensity from 1013w/cm2 to 1015w/cm2. The reliability of the PPT theoretical program and the calibration of the light intensity are verified. In this light intensity interval, the ionization curve of the Xe is in good agreement with the results of the PPT theory, and the simplification of the barrier is suppressed. The saturation light intensity obtained by the model ionization model is in agreement with the results given by the PPT theory. For the ionization of Kr at relatively low laser intensity, the contribution of the resonance amplification multiphoton ionization is observed experimentally. Using the obtained collimator as the research system, the laser intensity is collimated within the range of 1013w/ cm2 to 1015w/cm2, and the random distribution is distributed. The ionization dependent yield of the anti collimated iodide and methyl bromide molecules is measured, and the results are compared with the modified ppt theoretical simulation results. The contribution of the HOMO and the low molecular orbital to the ionization process in different light intensity ranges is analyzed in detail. The ionization of the random distribution of CH3Br molecules under the lower light intensity is analyzed. There is a deviation between the experimental results and the PPT theoretical prediction results. We attribute this partial deviation to the contribution of orbital ionization with A1 symmetry. The contribution of this part may come from the resonance excitation process; when the laser intensity is relatively high, the ionization is mainly through the contribution of the e orbit (Homo) perpendicular to the molecular axis. The ionization of iodide methane is in good agreement with the PPT theoretical simulation results, and its ionization mainly occurs through the e orbit (HOMO). The contribution of the different orbits to the ionization yield in the ionization process, namely the tribute of the Homo orbits and the low molecular orbital, is realized by the combination of the six pole transition dynamic selection technique and the laser collimation technique. An imaging measurement of the collimated and collimated multiphoton ionization electrons of iodide molecules by the angular resolution of the photoelectron velocity imaging. The different peaks in the electron spectrum are identified by the change of photoelectron spectroscopy with the change of light intensity. The collimation and collimation of the collimation and collimation are observed under the light intensity of 9.6 x 1012 W/cm2. The branching ratio of the two channels in the electron spectrum of the son is different. We attribute it to the change of the effective ionization potential with the change of the orientation of the molecular space.

【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】：TN24;O561

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