Improving Schlieren methods for measuring interface topography

Measuring the topography of a fluid-fluid interface allows to observe and quantify elusive
phenomena such as waves, instabilities or the presence of particles. For transparent fluids, this can be done with synthetic Schlieren methods. Among them, the so-called Moisy-Rabaud-Salsac (MRS) method is an elegant method that gives accurate measurements with a simple and low cost optical setup. It has been successfully used in the case of Faraday waves, wave-droplet interactions and floating objects. We propose an enhanced optical setup that uses a bitelecentric objective and a double pattern to measure larger slopes than the MRS method.