Ultrafast X-ray Science Laboratory, Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
J Chem Phys. 2012 Dec 28;137(24):244305. doi: 10.1063/1.4772199.
Light-induced coupling of core-excited states of Xe atoms is investigated by femtosecond extreme ultraviolet (XUV) transient absorption spectroscopy with photon energies ranging from 50 eV to 72 eV. Coupling of the 4d(-1)((2)D(5/2))6p((2)P(3/2)) (65.1 eV) and 4d(-1)((2)D(3/2))6p((2)P(1/2)) (67.0 eV) core-excited states to nearby states by a strong infrared laser field leads to a threefold enhancement of XUV transmission. The transmission at 65.1 eV (67.0 eV) changes from 3.2 ± 0.4% (5.9 ± 0.5%) without the coupling laser to 9 ± 2% (22 ± 5%) at the maximum of the laser field. A strong-field induced broad XUV absorption feature between 60 eV and 65 eV is ascribed to splitting of the field-free absorption lines into multiple branches when the Rabi frequencies of the coupling transitions exceed the infrared laser frequency. This picture is supported by a comparison of the strong-field induced absorption spectrum with a numerical integration of the von Neumann equation for a few-level quantum system. The valence hole-alignment of strong-field ionized Xe is revisited, confirming the previously observed reduced alignment compared to theoretical predictions.
采用飞秒极紫外（XUV）瞬态吸收光谱技术，研究了 Xe 原子芯激发态在光子能量为 50 eV 到 72 eV 范围内的光致耦合。通过强红外激光场，将 4d(-1)((2)D(5/2))6p((2)P(3/2))（65.1 eV）和 4d(-1)((2)D(3/2))6p((2)P(1/2))（67.0 eV）芯激发态耦合到附近态，导致 XUV 透射率增加了三倍。在没有耦合激光的情况下，65.1 eV（67.0 eV）处的透射率从 3.2 ± 0.4%（5.9 ± 0.5%）变化到激光场最大值时的 9 ± 2%（22 ± 5%）。当耦合跃迁的拉比频率超过红外激光频率时，在 60 eV 到 65 eV 之间出现了一个强场诱导的宽 XUV 吸收特征，这归因于无场吸收线分裂成多个分支。这一图像得到了强场诱导吸收光谱与几个能级量子系统的 von Neumann 方程数值积分的比较的支持。重新研究了强场电离 Xe 的价态空穴对准，证实了与理论预测相比，观察到的对准减少。
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