The soft-photon approximation in infrared-laser-assisted atomic ionization by extreme-ultraviolet attosecond-pulse trains
The soft-photon approximation in infrared-laser-assisted atomic ionization by extreme-ultraviolet attosecond-pulse trains
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DOI：
10.1088/1367-2630/15/11/113009
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发表时间：
2013-11
影响因子：
3.3
通讯作者：
Á. J. Galán;L. Argenti;F. Martín
中科院分区：
文献类型：
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作者：
Á. J. Galán;L. Argenti;F. Martín
我们使用软光子近似，制定有限的脉冲，调查的敷料脉冲的持续时间和强度的影响，模拟阿秒泵浦探测实验采用列车的阿秒极紫外脉冲结合红外探测脉冲。我们通过比较氦原子的模拟光电子分布，在光子能量区域接近N = 2阈值，从直接解的含时薛定谔方程的两个活性电子的结果，说明了近似的有效性。即使在自电离态的存在下，该模型准确地再现了1 s通道中的从头算光电子能谱的大部分背景特征。光电子谐波信号沿着偏振轴的分裂特别归因于探测脉冲的有限持续时间。此外，我们还研究了边带积分信号随泵浦探测时间延迟的变化规律。从大约101 TW cm-2的红外强度开始，由于三个或更多红外光子的交换，边带振荡中的泛音开始出现。我们推导出一个分析表达式的频率梳极限的软光子模型的所有边带频率分量的振幅，并表明，这些振幅振荡的红外场的强度的函数。特别地，我们预测，频率为2ωIR的基波分量的振幅，其基础上的激光光学重建技术，周期性地改变符号。
We use the soft-photon approximation, formulated for finite pulses, to investigate the effects of the dressing pulse duration and intensity on simulated attosecond pump–probe experiments employing trains of attosecond extreme-ultraviolet pulses in conjunction with an IR probe pulse. We illustrate the validity of the approximation by comparing the modelled photoelectron distributions for the helium atom, in the photon energy region close to the N = 2 threshold, to the results from the direct solution of the time-dependent Schrödinger equation for two active electrons. Even in the presence of autoionizing states, the model accurately reproduces most of the background features of the ab initio photoelectron spectrum in the 1s channel. A splitting of the photoelectron harmonic signal along the polarization axis, in particular, is attributed to the finite duration of the probe pulse. Furthermore, we study the dependence of the sideband integrated signal on the pump–probe time delay for increasing IR field strengths. Starting at IR intensities of the order of ∼ 1 TW cm−2, overtones in the sideband oscillations due to the exchange of three or more IR photons start to appear. We derive an analytical expression in the frequency-comb limit of the soft-photon model for the amplitude of all the sideband frequency components and show that these amplitudes oscillate as a function of the intensity of the IR field. In particular, we predict that the amplitude of the fundamental component with frequency 2ωIR, on which the rabitt optical reconstruction technique is based, changes sign periodically.