用超快电子衍射技术研究Al薄膜的超快动力学行为

Ultrafast dynamics of thin-film aluminum observed by ultrafast electron diffraction

超快电子衍射(UED)技术因其同时具有亚皮秒的时间分辨和亚毫埃的空间分辨能力,成为研究物质瞬态结构变化,特别是研究晶格材料超快动力学的有力工具.应用国内首台自行研制的UED系统,我们实时测量了超快激光脉冲激发下,20nm金属Al多晶薄膜产生的相干声子和晶格热运动.实验结果显示,在晶格热运动加剧的同时,热应力的作用使晶格产生了相干振荡,并最终膨胀达到新的平衡位置.实验中测得的振荡周期以及晶格上升的温度与理论计算的结果符合较好,展示了UED技术在超快晶格动力学研究方面的广阔应用前景.

Ultrafast electron diffraction （UED） is a powerful technique for the measurement of transient structures. Employing our UED system, with its capability of detecting a sub-milli-Angstrom lattice spacing change with a sub-picosecond temporal resolution, we performed the real-time observation of both the coherent phonon and thermal lattice motions of polycrystalline 20 nm A1 film, which was excited by femtosecond laser pulses. The obtained coherent oscillation period of ～ 7.4 ps and temperature rise of ～ 77 K agree well with those from theoretical calculation. This achievement offers great promise to conduct measurements of transient structures with atomic spatiotemporal resolution in many dynamical processes that can be initiated by uhrafast optical excitation.