During recent years, ray tracing has frequently been used to study the absorption characteristics of structured solar cells. However, wave properties such as absorption enhancement due to resonances in optically thin solar films, cannot be explained by pure classical ray models. Here we present an exact three-dimensional ray model for oblique incidence of a plane electromagnetic wave on a thin film and show that the resonant structure of the absorption cross section calculated from our ray model is identical to exact calculations by electromagnetic wave theory. Both parallel and perpendicular polarized light are described exactly by the ray model presented. We validate the resonant structure of the absorption cross section of our ray model by an experimentally realized layered film, where we obtain perfect agreement between experiment and theory. We demonstrate further that for a beam with a finite beam waist, in accordance with Beer-Lambert's law, absorption occurs along the path of the beam, while, in the case of a plane wave incident on an optically thin film, and contrary to Beer-Lambert's law, absorption occurs along the axis perpendicular to the surface of the film.

近年来，射线追踪经常被用于研究结构化太阳能电池的吸收特性。但是，纯光学经典模型无法解释诸如光学薄膜太阳能膜中的共振引起的诸如吸收增强之类的波特性。在这里，我们为平面电磁波在薄膜上的倾斜入射提供了精确的三维射线模型，并表明从我们的射线模型计算出的吸收截面的共振结构与电磁波理论的精确计算相同。平行偏振光和垂直偏振光均由所提供的射线模型精确描述。我们通过实验实现的多层膜验证了射线模型的吸收截面的共振结构，在此我们获得了实验与理论之间的完美契合。