用飞秒电子衍射技术对金属材料结构动力学进行超快时间分辨研究

项目名称： 用飞秒电子衍射技术对金属材料结构动力学进行超快时间分辨研究

项目编号： No.10874113

项目类型： 面上项目

立项/批准年度： 2009

项目学科： 电工技术

项目作者： 张杰

作者单位： 上海交通大学

项目金额： 50万元

中文摘要： 项目负责人领导的研究组建立了国内首套实用的超快电子衍射成像实验系统，具有优于500飞秒的时间分辨和亚毫埃的结构变化解析能力。利用该超快电子衍射系统，并结合超快光学与X射线衍射，我们在原子时空尺度对比了铝晶格薄膜在800纳米和1.25微米飞秒激光泵浦下的超快结构动力学过程，初步确认了由于800纳米激光对应于铝晶格的1.55电子伏特平行能带能隙，导致该波长泵浦下铝晶格结构变化同时存在热致和非热致过程；同时，我们研究了20纳米金膜由于应力应变而导致的晶格膨胀相对于晶格加热的时间延迟效应。我们还发展和完善了超快电子阴影成像法，并利用超快电子脉冲做为带电探针，首次采用了单发成像技术，研究了激光等离子体形成初期电荷分离场的演化过程,我们发现在前200ps电中性的等离子体尚未形成。

中文关键词： 超快电子衍射；超快结构动力学；电子-声子耦合；超快电子阴影成像；激光等离子体

英文摘要： PI's group has built the first practical ultrafast electron diffraction and imaging system in China with the temporal and structural change resolutions of 500 fs and 0.1 mili-Angstrom, respectively. First, the ultrafast structural dynamics of aluminum and gold excited by 800 and/or 1250 nm fs laser pulses were studied by ultrafast electron diffraction combined with femtosecond optical and x-ray studies. The preliminary results showed that the aluminum lattice dynamics involved both thermal and nonthermal processes induced by heating and 1.55 eV (800 nm) parallel band transition, respectively. The delayed response between the lattice expansion and heating as a result of the strain-stress effect has been observed in 20 nm Au films excited by 800 nm fs pulses. Second, the evolution of initial laser plasma charge separation has been studied by single-shot ultrafast electron shadowgraph technique, which showed that the formation of the electrical neutral plasma is longer than 200 ps.

英文关键词： Ultrafast electron diffraction; ultrfast structural dynamics; electron-phonon coupling; ultrafast electron shadowgraph