Zandi Omid, Wilkin Kyle J, Xiong Yanwei, Centurion Martin
Department of Physics and Astronomy, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, USA.
Struct Dyn. 2017 May 8;4(4):044022. doi: 10.1063/1.4983225. eCollection 2017 Jul.
We have constructed an experimental setup for gas phase electron diffraction with femtosecond resolution and a high average beam current. While gas electron diffraction has been successful at determining molecular structures, it has been a challenge to reach femtosecond resolution while maintaining sufficient beam current to retrieve structures with high spatial resolution. The main challenges are the Coulomb force that leads to broadening of the electron pulses and the temporal blurring that results from the velocity mismatch between the laser and electron pulses as they traverse the sample. We present here a device that uses pulse compression to overcome the Coulomb broadening and deliver femtosecond electron pulses on a gas target. The velocity mismatch can be compensated using laser pulses with a tilted intensity front to excite the sample. The temporal resolution of the setup was determined with a streak camera to be better than 400 fs for pulses with up to half a million electrons and a kinetic energy of 90 keV. The high charge per pulse, combined with a repetition rate of 5 kHz, results in an average beam current that is between one and two orders of magnitude higher than previously demonstrated.
我们构建了一个用于气相电子衍射的实验装置，具有飞秒分辨率和高平均束流。虽然气体电子衍射在确定分子结构方面取得了成功，但在保持足够的束流以获取高空间分辨率结构的同时达到飞秒分辨率一直是一个挑战。主要挑战包括导致电子脉冲展宽的库仑力，以及激光脉冲和电子脉冲在穿过样品时由于速度不匹配而产生的时间模糊。我们在此展示一种利用脉冲压缩来克服库仑展宽并将飞秒电子脉冲作用于气体靶的装置。可以使用具有倾斜强度前沿的激光脉冲来激发样品，从而补偿速度不匹配。使用条纹相机确定该装置的时间分辨率对于具有多达五十万个电子且动能为90 keV的脉冲优于400 fs。每个脉冲的高电荷量与5 kHz的重复率相结合，使得平均束流比之前展示的高出一到两个数量级。
