金属表面的相干二维多光子光电子能谱学
Coherent two-dimensional multiphoton photoelectron spectroscopy of metal surfaces
摘要：
光与金属相互作用产生了亚飞秒到几飞秒时间尺度的超快相干多体屏蔽响应，这使得实验观测具有挑战性。在这里，我们描述的相干二维（2D）多光子光电子能谱研究的肖克莱表面态（SS）的Ag（111）作为基准的光谱学的相干非线性响应的金属光场在微扰制度。采用干涉时间分辨多光子光电子能谱（ITR-mPP），我们相关的相干偏振和人口在样品中激发的最终光电子分布的相互作用终止。通过测量SS态的非共振3-和4-光子光电子能谱，以及其在阈上光电子能谱（ATP）中的复制结构，我们用二维光电子能谱记录了Ag（111）表面的相干响应，并将其与其能带结构联系起来。我们解释的mPP过程中的光学布洛赫方程（OBE）模型，再现ITR-mPP实验中记录的表面态相干极化动力学的主要特点：二维光电子谱的光谱分量示出依赖于非线性阶的相干光电发射过程m以及上的诱导相干n。
英文摘要：
Light interacting with metals elicits an ultrafast coherent many-body screening response on sub- to few-femtosecond time-scales, which makes its experimental observation challenging. Here, we describe the coherent two-dimensional (2D) multi-photon photoemission study of the Shockley surface state (SS) of Ag(111) as a benchmark for spectroscopy of the coherent nonlinear response of metals to an optical field in the perturbative regime. Employing interferometrically time-resolved multi-photon photoemission spectroscopy (ITR-mPP), we correlate the coherent polarizations and populations excited in the sample with final photoelectron distributions where the interaction terminates. By measuring the non-resonant 3- and 4-photon photoemission of the SS state, as well as its replica structures in the above-threshold photoemission (ATP), we record the coherent response of the Ag(111) surface by 2D photoemission spectroscopy and relate it to its band structure. We interpret the mPP process by an optical Bloch equation (OBE) model, which reproduces the main features of the surface state coherent polarization dynamics recorded in ITR-mPP experiments: The spectroscopic components of the 2D photoelectron spectra are shown to depend on the nonlinear orders of the coherent photoemission process m as well as on the induced coherence n.
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