In the present work, an efficient method is theoretically investigated for extending high-order harmonics and ultrashort attosecond pulse generation in N₂ 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.

中文翻译：

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在低频场存在下对CO和N2分子高次谐波产生的电子量子轨迹的控制

在目前的工作中，理论上研究了一种有效的方法来扩展N _2中的高次谐波和超短阿秒脉冲的产生和CO分子采用时变密度泛函理论方法。我们的结果表明，在存在低频场的情况下利用chi激光场，不仅谐波截止频率显着延长，而且选择了单个短量子轨迹来构成谐波频谱。当将低频场添加到双色chi激光场时，长量子轨迹被抑制，只有短量子轨迹才有助于更高的谐波发射机制。结果，频谱调制显着降低，并且可以从高谐波的超连续谱区域产生强烈的超短脉冲。使用这种方案，可以在长度，速度和加速度计中生成隔离的超短阿秒脉冲。此外，