We describe a basic theoretical treatment of how film–substrate and substrate–environment (air, water, and solution) interfaces can be selectively probed by controlling the film thickness and beam angles in a visible-infrared sum frequency generation experiment. In this model, we also account for the unique interfacial environment that may have optical properties that differ from the adjacent bulk phases. We see that this affects components of the electric field that are perpendicular to the surface such as when p-polarized light is used. We then provide an example using the glass–polydimethylsiloxane–air system and model the fields at both surfaces of the polymer. This is followed by some practical considerations for setting up such experiments and some typical experimental results.

中文翻译：

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薄膜界面的振动和频谱

我们描述了如何通过控制可见红外和频产生实验中的薄膜厚度和光束角来选择性地探测薄膜-基材和基材-环境（空气、水和溶液）界面的基本理论处理。在这个模型中，我们还考虑了可能具有与相邻体相不同的光学特性的独特界面环境。我们看到这会影响垂直于表面的电场分量，例如在使用 p 偏振光时。然后，我们提供了一个使用玻璃-聚二甲基硅氧烷-空气系统的示例，并对聚合物两个表面的场进行建模。接下来是设置此类实验的一些实际考虑因素和一些典型的实验结果。