Simulating and interpretating images of foams with computational ray-tracing techniques

Liquid foams consist of complex arrangements of gas/liquid interfaces, which form intricate refractive systems. The interpretation of images of foams has therefore always been a challenge and highly sensitive to optical illusions. These difficulties can be overcome by combining experiments with computational ray-tracing techniques, which we demonstrate in detail for two systems of particular interest to foam research: the imaging of ordered bubble crystals and mono-layers of foams between glass plates in front of a diffusive light source. Using a 3D-animation program (3D Studio Max) and a simplified 2D ray-tracing model, we illustrate the underlying principles and establish some fundamental relationships between the geometry and the images of these foam structures. Experimentalists are encouraged to adapt these methods to their own needs.