Make a Halo with Diffuse, Specular, and Total Internal Reflection

In this presentation, we explore the fascinating and educational physics behind the halo formed by a laser spot in shallow water. Using geometric optics, we present a straightforward model to explain this phenomenon, supported by empirical evidence. We also delve into extensions of this model that account for variations in the visual pattern, such as a double halo pattern and a disk of dim light. Despite varying complexities, all models are grounded in the principles of ray optics, including refraction, and diffuse, specular, and total internal reflection. We will discuss practical ways to incorporate these halo effects into undergraduate physics courses, offering a rich, real-world application of key optics concepts suitable for diverse teaching environments.