Improved Schlieren method for fluid-fluid interface topography
new publication in Experiments in Fluids
Our paper, about an improved Schlieren method for measuring the elevation of fluid-fluid interfaces, is available in Experiments in Fluids : https://rdcu.be/cSIMp
The Schlieren method intends to reveal the elevation of some refractive fluid-fluid interface. For example, it allows to measure capillary waves propagating along the air-water surface. Or, the method is used to measure the capillary interaction between floating objects via their respective surface deformations.
The method is based on a comparison of images of a single pattern placed at the bottom of the container. Accurate measurements can be obtained with a simple and low cost optical setup. However, it is restricted to weak interface deformations, weak slopes and weak paraxial angles.
To overcome these limitations, we proposed an enhanced optical setup that uses a bitelecentric objective and a double pattern. Thanks to this new setup, we avoid geometrical approximations and we extend the method to moderate/large deformations. Moreover, the proposed method has the great advantage to become independent on the liquid depth and could be used in various applications.
The images below shows from left to right the setup, the sketch of the principle and the measurements using one or two patterns for glass wedges.