Laboratoire de Chimie Physique, CNRS, University of Paris-Sud, Université Paris-Saclay, Bâtiment 201 P2, 91405 Orsay, France.
J Chem Phys. 2018 Jul 21;149(3):034701. doi: 10.1063/1.5027154.
We present a modeling of the nonlinear optical response of a metal surface in order to account for recent experimental results from two-color Sum-Frequency Generation (SFG) experiments on gold. The model allows calculating the surface and bulk contributions and explicitly separates free and bound electron terms. Contrary to the other contributions, the perpendicular surface component is strongly model-dependent through the surface electron density profiles. We consider three electron density schemes at the surface, with free and bound electrons overlapping or spilling out of the bulk, for its calculation. The calculated SFG signals from the metal rely only on bulk quantities and do not need an explicit definition of the density profiles. In the particular case of gold, when the free electrons overlap with the bound ones or spill out of the bulk, the free electron response completely dominates through the perpendicular surface terms. When the bound electrons spill out, the situation is more balanced, still in favor of the free electrons, with lower amplitudes and different dispersion line shapes. As for silver, the free electron contributions dominate and the calculated slow amplitude growth from blue to red follows the experimental trends.
我们提出了一种金属表面非线性光学响应的建模方法，以便解释最近在双色和频（SFG）实验中对金的实验结果。该模型允许计算表面和体贡献，并明确分离自由电子和束缚电子项。与其他贡献相反，垂直于表面的分量强烈依赖于表面电子密度分布，需要通过表面电子密度分布来计算。我们考虑了三种表面电子密度方案，其中自由电子和束缚电子相互重叠或溢出体相，用于计算。金属的 SFG 信号仅依赖于体相数量，不需要明确定义密度分布。在金的特殊情况下，当自由电子与束缚电子重叠或溢出体相时，自由电子响应完全通过垂直于表面的项来主导。当束缚电子溢出时，情况更加平衡，仍然有利于自由电子，但其幅度较低，色散线形状不同。对于银，自由电子贡献占主导地位，从蓝色到红色的计算缓慢幅度增长与实验趋势一致。
