Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, Germany.
Department of Chemistry, University of California, Berkeley, California 94720, USA.
Phys Rev Lett. 2019 Oct 18;123(16):163201. doi: 10.1103/PhysRevLett.123.163201.
We report on the experimental observation of a strong-field dressing of an autoionizing two-electron state in helium with intense extreme-ultraviolet laser pulses from a free-electron laser. The asymmetric Fano line shape of this transition is spectrally resolved, and we observe modifications of the resonance asymmetry structure for increasing free-electron-laser pulse energy on the order of few tens of Microjoules. A quantum-mechanical calculation of the time-dependent dipole response of this autoionizing state, driven by classical extreme-ultraviolet (XUV) electric fields, evidences strong-field-induced energy and phase shifts of the doubly excited state, which are extracted from the Fano line-shape asymmetry. The experimental results obtained at the Free-Electron Laser in Hamburg (FLASH) thus correspond to transient energy shifts on the order of a few meV, induced by strong XUV fields. These results open up a new way of performing nonperturbative XUV nonlinear optics for the light-matter interaction of resonant electronic transitions in atoms at short wavelengths.
我们报告了在氦中用自由电子激光的强极端紫外激光脉冲对自电离双电子态的强场修饰的实验观察。该跃迁的非对称 Fano 线型在光谱上得到了分辨，我们观察到随着自由电子激光脉冲能量的增加，共振不对称结构的修饰约为几十微焦耳。通过对这个自电离态的时间相关偶极响应的量子力学计算，由经典的极端紫外（XUV）电场驱动，证明了双激发态的强场诱导的能量和相位移动，这是从 Fano 线型不对称中提取出来的。在汉堡自由电子激光（FLASH）中获得的实验结果对应于由强 XUV 场诱导的约几毫电子伏特的瞬态能量移动。这些结果为原子中共振电子跃迁的光物质相互作用开辟了一种新的进行非微扰 XUV 非线性光学的方法，用于短波长。
