Ciappina M F, Aćimović Srdjan S, Shaaran T, Biegert J, Quidant R, Lewenstein M
ICFO-Institut de Ciènces Fotòniques, Barcelona, Spain.
Opt Express. 2012 Nov 19;20(24):26261-74. doi: 10.1364/OE.20.026261.
We study high-order harmonic generation (HHG) resulting from the illumination of plasmonic nanostructures with a short laser pulse of long wavelength. We demonstrate that both the confinement of the electron motion and the inhomogeneous character of the laser electric field play an important role in the HHG process and lead to a significant increase of the harmonic cutoff. In particular, in bow-tie nanostructures with small gaps, electron trajectories with large excursion amplitudes experience significant confinement and their contribution is essentially suppressed. In order to understand and characterize this feature, we combine the numerical solution of the time-dependent Schrödinger equation (TDSE) with the electric fields obtained from 3D finite element simulations. We employ time-frequency analysis to extract more detailed information from the TDSE results and classical tools to explain the extended harmonic spectra. The spatial inhomogeneity of the laser electric field modifies substantially the electron trajectories and contributes also to cutoff increase.
我们研究了用长波长短激光脉冲照射等离子体纳米结构所产生的高次谐波产生（HHG）。我们证明，电子运动的限制和激光电场的非均匀特性在HHG过程中都起着重要作用，并导致谐波截止频率显著增加。特别是，在具有小间隙的蝴蝶结形纳米结构中，具有大偏移幅度的电子轨迹受到显著限制，其贡献基本上被抑制。为了理解和表征这一特征，我们将含时薛定谔方程（TDSE）的数值解与从三维有限元模拟获得的电场相结合。我们采用时频分析从TDSE结果中提取更详细的信息，并使用经典工具来解释扩展的谐波光谱。激光电场的空间不均匀性极大地改变了电子轨迹，也有助于截止频率的增加。
