Imaging ultrafast molecular dynamics with laser-induced electron diffraction
Imaging ultrafast molecular dynamics with laser-induced electron diffraction
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DOI：
10.1038/nature10820
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发表时间：
2012-03-08
期刊：
影响因子：
64.8
通讯作者：
Lin, C. D.
中科院分区：
文献类型：
--
作者：
Blaga, Cosmin I.;Xu, Junliang;Lin, C. D.
确定分子和固体的结构在物理、化学和生物学中一直起着至关重要的作用。首选的方法是X射线和电子衍射，它们通常用于以亚埃的空间分辨率确定原子位置。尽管这两种方法目前都局限于探测皮秒以上时间尺度的动力学，但最近飞秒X射线脉冲源和电子束源的发展表明，它们可能很快就能对发生结构变化的生物分子（1,2）和凝聚相系统（3 - 6）进行超快拍摄。过去十年还见证了一种基于激光电离的相干电子波包脉冲的替代成像方法的出现，这些电子波包会对母体分子结构进行自我探测（7 - 11）。在此我们表明，这种现象确实可用于激光诱导电子衍射（10）（LIED），以亚埃精度和几飞秒的曝光时间对分子结构成像。我们将该方法应用于氧分子和氮分子，它们在三个中红外波长（1.7、2.0和2.3μm）的强场电离下发射出光电子，我们从其动量分布中提取出衍射图案。长波长对于实现原子级空间分辨率至关重要，而波长变化相当于在不同时间拍摄快照。我们表明，该方法能够灵敏地测量在约5 fs的时间间隔内氧键长度0.1埃的位移，这确立了LIED作为一种以前所未有的时空分辨率对气相分子成像的有前途的方法。
Establishing the structure of molecules and solids has always had an essential role in physics, chemistry and biology. The methods of choice are X-ray and electron diffraction, which are routinely used to determine atomic positions with sub-a ngstrom spatial resolution. Although both methods are currently limited to probing dynamics on timescales longer than a picosecond, the recent development of femtosecond sources of X-ray pulses and electron beams suggests that they might soon be capable of taking ultrafast snapshots of biological molecules(1,2) and condensed-phase systems(3-6) undergoing structural changes. The past decade has also witnessed the emergence of an alternative imaging approach based on laser-ionized bursts of coherent electron wave packets that self-interrogate the parent molecular structure(7-11). Here we show that this phenomenon can indeed be exploited for laser-induced electron diffraction(10) (LIED), to image molecular structures with subangstrom precision and exposure times of a few femtoseconds. We apply the method to oxygen and nitrogen molecules, which on strong-field ionization at three mid-infrared wavelengths (1.7, 2.0 and 2.3 mu m) emit photoelectrons with a momentum distribution from which we extract diffraction patterns. The long wavelength is essential for achieving atomic-scale spatial resolution, and the wavelength variation is equivalent to taking snapshots at different times. We show that the method has the sensitivity to measure a 0.1 angstrom displacement in the oxygen bond length occurring in a time interval of similar to 5 fs, which establishes LIED as a promising approach for the imaging of gas-phase molecules with unprecedented spatio-temporal resolution.