Caustics and symmetries in optical imaging. The example of convective flow visualization

(Received 19 January 1994, accepted 18 March 1994)

Abstract
It is shown that qualitative and quantitative information can be collected from the study of the full caustic formed by light rays deflected by some medium. The study necessitates the calculation of the ray trajectories along with a detailed balance of the symmetries of the whole setup. As an example we consider the case of the caustic produced by parallel rays interacting with a periodic convective flow in a liquid crystal. The amplitude of the flow and ail its essential features can be deduced, indicating that a caustic carries more information than a simple image.