Mizuse Kenta, Sakamoto Naoya, Fujimoto Romu, Ohshima Yasuhiro
Department of Chemistry, School of Science, Tokyo Institute of Technology, 2-12-1-W4-9 Ookayama, Meguro, Tokyo 152-8550, Japan.
Phys Chem Chem Phys. 2020 May 21;22(19):10853-10862. doi: 10.1039/d0cp01084g. Epub 2020 May 6.
High-precision, time-resolved Coulomb explosion imaging of rotational wave packets in nitrogen molecules created with a pair of time-delayed, polarization-skewed femtosecond laser pulses is presented, providing insight into the creation process and dynamics of direction-controlled wave packets. To initiate unidirectional rotation, the interval of the double-pulse was set so that the second, polarization-tilted pulse hit the molecules at the time when molecules were aligned or antialigned along the polarization vector of the first pulse. During the revival period of the rotational wave packet, pulse intervals around both the full and half revival times were used. The observed molecular wave packet movies clearly show the signatures of quantum rotation, such as angular localization (alignment), dispersion, and revival phenomena, during the unidirectional motion. The patterns are quite different depending on the pulse interval even when the angular distribution at the second pulse irradiation is similar. The observed interval-dependence of the dynamics was analyzed on the basis of the real-time images, with the aid of numerical simulations, and the creation process of the packets was discussed. We show that the observed image patterns can be essentially rationalized in terms of rotational period and alignment parameter. Because the double-pulse scheme is the most fundamental in the creation of direction-controlled rotational wave packets, this study will lead to more sophisticated control and characterization of directional molecular motions.
本文介绍了利用一对具有时间延迟、偏振倾斜的飞秒激光脉冲产生的氮分子中旋转波包的高精度、时间分辨库仑爆炸成像，这有助于深入了解方向可控波包的产生过程和动力学。为了启动单向旋转，设置双脉冲的时间间隔，使得第二个偏振倾斜脉冲在分子沿第一个脉冲的偏振矢量排列或反排列时撞击分子。在旋转波包的复苏期，使用了围绕全复苏时间和半复苏时间的脉冲间隔。观察到的分子波包电影清楚地显示了单向运动过程中量子旋转的特征，如角局域化（排列）、色散和复苏现象。即使在第二个脉冲照射时的角分布相似的情况下，图案也会因脉冲间隔的不同而有很大差异。借助数值模拟，基于实时图像分析了观察到的动力学对间隔的依赖性，并讨论了波包的产生过程。我们表明，观察到的图像图案基本上可以根据旋转周期和排列参数来合理化。由于双脉冲方案是产生方向可控旋转波包最基本的方法，这项研究将导致对定向分子运动进行更精确的控制和表征。
