Resonantly-initiated quantum trajectories and their role in the generation of near-threshold harmonics
Resonantly-initiated quantum trajectories and their role in the generation of near-threshold harmonics
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DOI：
10.1088/1361-6455/aaac12
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发表时间：
2018-02
期刊：
影响因子：
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通讯作者：
S. Camp;S. Beaulieu;K. Schafer;M. Gaarde
中科院分区：
文献类型：
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作者：
S. Camp;S. Beaulieu;K. Schafer;M. Gaarde
我们提出了一个理论研究的作用，共振增强的时间和光谱特性的近阈值谐波在氩气中，由一个中等强度的近红外激光脉冲驱动。通过研究第十一次谐波（H11）的时间轮廓如何随峰值强度和脉冲持续时间的变化，我们表明，H11主要是发射时，激光脉冲的瞬时强度是这样的，一个高躺的激发态是斯塔克移动到与基态的多光子共振。我们证明，如果这个共振强度低于峰值强度，谐波脉冲将在一般情况下表现出两个峰值的时间，在上升沿和下降沿的激光脉冲。共振增强的谐波辐射表现出强烈的半经典长、短量子路径特征，一般两条路径都被共振增强。我们发现，共振增强导致谐波辐射被发射的时间后的多光子共振的.5和1.1光学周期之间，这表明共振引入了一个延迟相比，非共振发射。我们进一步证明，共振增强的长轨迹的谐波辐射的贡献表现在光谱域的红，蓝移功能附近的中心谐波频率。最后，我们比较了单个氩原子的宏观响应的氩气，并表明，光谱和时间效应的共振传播后仍然是可识别的。
We present a theoretical study of the role that resonant enhancement plays in the temporal and spectral properties of near-threshold harmonics in argon, driven by a moderately intense, near-infrared laser pulse. By studying how the temporal profile of the eleventh harmonic (H11) changes with peak intensity and pulse duration, we show that H11 is predominantly emitted when the instantaneous intensity of the laser pulse is such that a high-lying excited state is Stark-shifted into multiphoton resonance with the ground state. We demonstrate that if this resonant intensity is lower than the peak intensity, the harmonic pulse will in general exhibit two peaks in time, on the rising and falling edges of the laser pulse. The resonantly enhanced harmonic radiation exhibits strong characteristics of semi-classical long and short quantum paths, and in general both paths are enhanced by the resonance. We find that the resonant enhancement leads to the harmonic radiation being emitted between .5 and 1.1 optical cycles after the time of multiphoton resonance, indicating that the resonance introduces a delay as compared to non-resonant emission. We further demonstrate that the resonantly enhanced long-trajectory contribution to the harmonic radiation manifests in the spectral domain as red- and blueshifted features near the central harmonic frequency. Finally, we compare the single argon atom response to the macroscopic response of an argon gas and show that spectral and temporal effects of the resonance are still recognizable after propagation.