Coherent phonon excitation and linear thermal expansion in structural dynamics and ultrafast electron diffraction of laser-heated metals.
Coherent phonon excitation and linear thermal expansion in structural dynamics and ultrafast electron diffraction of laser-heated metals.
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DOI：
10.1063/1.2901028
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发表时间：
2008-04
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影响因子：
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通讯作者：
Jau Tang
中科院分区：
文献类型：
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作者：
Jau Tang
在这项研究中，我们研究的超快结构动力学的金属诱导的飞秒激光加热脉冲探测的时间分辨电子衍射。使用双温度模型和Grüneisen关系，我们计算的电子温度，声子温度，和冲击力在每个原子的位置在板。结合Fermi-Pasta-Ulam非简谐链模型，计算了键距的变化和布拉格点或劳厄环的峰位移。激光加热的薄板表现出“呼吸”驻波行为，其周期等于声波的往返时间，波长是板厚的两倍。峰值延迟时间首先随厚度线性增加（对于铝<70 nm，对于金<200 nm），但如果厚度进一步增加，则变得不太依赖。相干声子激发和传播的应力体原子由于脉冲力以及线性热膨胀，由于晶格温度跳示，有助于整体结构的变化。这两种机制之间的差异和它们对膜厚和其他因素的依赖性进行了讨论。
In this study, we examine the ultrafast structural dynamics of metals induced by a femtosecond laser-heating pulse as probed by time-resolved electron diffraction. Using the two-temperature model and the Grüneisen relationship we calculate the electron temperature, phonon temperature, and impulsive force at each atomic site in the slab. Together with the Fermi-Pasta-Ulam anharmonic chain model we calculate changes of bond distance and the peak shift of Bragg spots or Laue rings. A laser-heated thin slab is shown to exhibit "breathing" standing-wave behavior, with a period equal to the round-trip time for sound wave and a wavelength twice the slab thickness. The peak delay time first increases linearly with the thickness (<70 nm for aluminum and <200 nm for gold), but becomes less dependent if further thickness increases. Coherent phonon excitation and propagation from the stressed bulk atoms due to impulsive forces as well as the linear thermal expansion due to lattice temperature jump are shown to contribute to the overall structural changes. Differences between these two mechanisms and their dependence on film thickness and other factors are discussed.