X-ray two-photon absorption competing against single and sequential multiphoton processes
X-ray two-photon absorption competing against single and sequential multiphoton processes
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DOI：
10.1038/nphoton.2014.10
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发表时间：
2014-02
期刊：
影响因子：
35
通讯作者：
K. Tamasaku;E. Shigemasa;Y. Inubushi;T. Katayama;K. Sawada;H. Yumoto;H. Ohashi;H. Mimura;M. Yabash
中科院分区：
文献类型：
--
作者：
K. Tamasaku;E. Shigemasa;Y. Inubushi;T. Katayama;K. Sawada;H. Yumoto;H. Ohashi;H. Mimura;M. Yabash
X射线自由电子激光(XFELs)的成功将非线性光学的前沿扩展到了硬X射线领域。最近，已经报道了和频产生以及参数下转换。这些是最低(第二)级的过程，而更高级的过程仍未被探索。在这里，我们首次观测到了一个三级过程：Ge对5.6keV的XFEL光束的双光子吸收。我们发现双光子吸收与单光子和顺序多光子过程竞争，但我们通过分析脉冲能量依赖关系成功地确定了本征截面。我们还通过比较X射线特有的新机制和传统的机制讨论了双光子吸收截面，表明后者与目前的结果是一致的。对截面的实验测定和理解将使双光子吸收光谱成为可能。我们的结果表明，X射线类似于其他三阶非线性光学过程，如非线性拉曼效应和光学克尔效应，可用于XFEL在光谱、成像和光束控制方面的应用。
The success,of X-ray free-electron lasers (XFELs) has extended the frontier of nonlinear optics into the hard X-ray region. Recently, sum-frequency generation has been reported, as well as parametric downconversion,,. These are of the lowest (second) order, and higher-order processes remain unexplored. Here, we report the first observation of a third-order process: two-photon absorption of a 5.6 keV XFEL beam by germanium. We find that two-photon absorption competes with single and sequential multiphoton processes,, but we successfully determine the intrinsic cross-section by analysing the pulse-energy dependence. We also discuss the two-photon absorption cross-section by comparing a new mechanism unique to X-rays with the conventional mechanism and show that the latter is consistent with the present result. The experimental determination and understanding of the cross-section would allow two-photon absorption spectroscopy. Our result indicates that X-ray analogues of other third-order nonlinear optical processes, such as nonlinear Raman and optical Kerr effects, are available for XFEL applications in spectroscopy, imaging and beam control.