Diffusion of light through surfaces and volumes

Although Descartes' laws (n sin i = constant) are commonly taught from the very first learning of optics, they only apply to a limited number of low-roughness surfaces. Conversely, light scattering phenomena, which govern a vast majority of phenomena including imaging and vision, are still little taught. The aim of this article is to provide non-specialist engineers and researchers with the theoretical and experimental tools they need to understand and apply these phenomena pragmatically.

In this paper, we will detail a perturbative approach characteristic of random media (surfaces and volumes) responsible for a weak diffusion in front of the incident flux; this approach presents multiple interests:

• Modelling is simple to implement, with reduced calculation times that allow three-dimensional and spectral processing;

• the case of diffusing volumes is treated in a similar way to that of rough surfaces;

• generalization to multilayer planar structures (interference filters and waveguides) is immediate;

• from an electromagnetic point of view, the problem of diffusion in multilayer systems is identical to that of luminescent microcavities;

• finally, the perturbative approach reveals analytical expressions that are extremely useful in guiding the experimenter or theorist towards new applications; once the application has been identified, rigorous models can be used to establish a domain of validity and gain in precision.