Multiplexed digital holography for fluid surface profilometry

Digital holography (DH) has been widely used for imaging and characterization of microstructures and nanostructures in materials science and biology and also has the potential to provide high-resolution, nondestructive measurement of fluid surfaces. DH setups capture the complex wavefronts of light scattered by an object or reflected from a surface, allowing the quantitative measurements of their shape and deformation. However, their use in fluid profilometry is scarce and has not been explored in much depth to the best of our knowledge. We present an alternative use for a DH setup that can measure and monitor the surface of fluid samples. Based on DH reflectometry, our modeling shows that multiple reflections from the sample and the reference interfere and generate multiple holograms of the sample, resulting in a multiplexed image of the wavefront. The individual interferograms can be isolated in the spatial frequency domain, and the fluid surface can be digitally reconstructed from them. We further show that this setup can be used to track changes in the surface of a fluid over time, such as during the formation and propagation of waves or the evaporation of surface layers.