ABSTRACT

Based on the three-step model of high harmonic generation, we propose a scheme to improve the harmonic spectra and to produce the intense water window attosecond pulses. It is found that, firstly, by introducing the single chirp and two chirps modulations, the instantaneous frequency on the falling part of the laser field is decreased. As a result, the electron can obtain larger energy during the acceleration-recombination process, showing a broad harmonic plateau in the water window region. Secondly, by properly adding a third controlling IR or UV pulse, the ionization process can be controlled and a larger ionization probability can be found, which leads to the enhancement of the harmonic intensity by 1 or 2 orders of magnitudes, respectively. Most important, using this scheme, the harmonic plateau is only contributed by the intense single harmonic emission peak, which can support the generation of an intense 36 as pulse.

摘要

基于高次谐波产生的三步模型，我们提出了一种改善谐波频谱并产生强烈的水窗阿秒脉冲的方案。发现，首先，通过引入单线性调频和两个线性调频调制，降低了激光场下降部分的瞬时频率。结果，电子可以在加速复合过程中获得更大的能量，在水窗区域显示出宽泛的谐波平稳期。其次，通过适当添加第三个控制IR或UV脉冲，可以控制电离过程，并且可以找到更大的电离概率，从而分别将谐波强度提高了1个或2个数量级。最重要的是，使用此方案，