Department of Physical Chemistry, Faculty of Chemistry, University of Kashan, P. O. Box 87317-51167, Kashan, Iran.
Department of Physics, Sharif University of Technology, Tehran, Iran.
J Chem Phys. 2018 Apr 14;148(14):144306. doi: 10.1063/1.5018819.
In the present work, an efficient method is theoretically investigated for extending high-order harmonics and ultrashort attosecond pulse generation in N and CO molecules by using the time-dependent density functional theory approach. Our results show that by utilizing chirped laser field in the presence of a low frequency field, not only is the harmonic cutoff extended remarkably but also the single short quantum trajectory is selected to contribute to the harmonic spectra. When a low frequency field is added to the two-color chirped laser field, the long quantum trajectories are suppressed and only the short quantum trajectories contribute to the higher harmonic emission mechanism. As a result, the spectral modulation is significantly decreased and an intense ultrashort pulse can be generated from the supercontinuum region of high harmonics. With such a scheme, the isolated ultrashort attosecond pulses can be generated in length, velocity, and acceleration gauges. Furthermore, these results are explained by using the classical and quantum time-frequency analyses.
在本工作中，我们理论上研究了一种通过利用含时密度泛函理论方法来扩展 N 和 CO 分子中的高阶谐波和超短阿秒脉冲的有效方法。我们的结果表明，通过在低频场存在下使用啁啾激光场，不仅可以显著扩展谐波截止，而且还可以选择单个短量子轨迹来贡献谐波谱。当低频场被添加到双色啁啾激光场中时，长量子轨迹被抑制，只有短量子轨迹有助于更高阶谐波发射机制。因此，光谱调制显著降低，可以从高谐波的超连续区产生强烈的超短脉冲。通过这样的方案，可以在长度、速度和加速度计中产生孤立的超短阿秒脉冲。此外，这些结果通过经典和量子时频分析得到了解释。
