This article provides a comprehensive theoretical background of electronic sum frequency generation (ESFG), a second-order nonlinear spectroscopy technique. ESFG is utilized to investigate both exposed and buried interfaces, which are challenging to study using conventional spectroscopic methods. By overlapping two incident beams at the interface, ESFG generates a beam at the sum of their frequencies, allowing for the extraction of valuable interfacial molecular information such as molecular orientation and density of states present at interfaces. The unique surface selectivity of ESFG arises from the absence of inversion symmetry at the interfaces. However, detecting weak signals from interfaces requires the ultrafast lasers to generate a sufficiently strong signal. By understanding the theoretical foundations of ESFG presented in this article, readers can gain a solid grasp of the basics of ESFG spectroscopy.

中文翻译：

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用于评估埋藏界面的电子和频发生谱的理论研究。

本文提供了电子和频生成 (ESFG)（一种二阶非线性光谱技术）的全面理论背景。ESFG 用于研究暴露和掩埋界面，这对于使用传统光谱方法进行研究具有挑战性。通过在界面处重叠两束入射光束，ESFG 生成频率总和的光束，从而可以提取有价值的界面分子信息，例如界面处存在的分子取向和状态密度。ESFG 独特的表面选择性源于界面处不存在反演对称性。然而，检测来自接口的微弱信号需要超快激光器产生足够强的信号。通过了解本文介绍的 ESFG 理论基础，读者可以扎实掌握 ESFG 光谱学的基础知识。