Abstract

We present a study of the possibility to significantly enhance the efficiency of high-order harmonic generation (HHG) using few-cycle optical waveforms obtained by superposing two laser pulses of different color delayed optimally relative to each other. Special attention is paid to the dynamics of the depopulation of atomic states, which, on the one hand, promotes electrons to the continuum to take part in the high-energy photon emission, but, on the other hand, depletes the nonlinear medium. The use of the waveforms proposed here gives extra flexibility to control both the bound-state depopulation and the electron acceleration in the continuum. We demonstrate that the approach proposed here allows to increase the efficiency of optical frequency conversion into sub-keV or few-keV photon energy ranges by up to an order of magnitude. High efficiency of HHG in optimal conditions is explained by the peculiarities of the photoelectron dynamics, which are characterized in this case by the combination of high-probability ejection of the electron responsible for the highest-order harmonic production and its subsequent strong acceleration accompanied by a relatively low probability of the bound-state depletion during the time interval between ionization and recollision.

中文翻译：

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通过控制原子电子子周期的分离和加速动力学，在短脉冲双色激光场中增强高次谐波的产生

摘要

我们目前正在研究一种可能性，即通过使用几个周期的光波形来显着提高高次谐波生成（HHG）的效率，这些波形通过叠加两个彼此相对最佳延迟的不同颜色的激光脉冲而获得。特别要注意原子态减少的动力学，原子态减少一方面会促进电子进入连续体，参与高能光子的发射，另一方面会耗尽非线性介质。此处提出的波形的使用为控制束缚态人口和连续体中的电子加速度提供了额外的灵活性。我们证明，这里提出的方法可以将光频率转换为亚keV或少数keV光子能量范围的效率提高一个数量级。