  Digital holography (DH) has been widely used for imaging and characterization
of micro and nanostructures in materials science and biology and has the
potential to provide high-resolution, non-destructive measurements of fluid
surfaces as well. Digital holographic setups capture the complex wavefronts of
light scattered by an object or reflected from a surface, allowing for
quantitative measurements of their shape and deformation. However, their use in
fluid profilometry is scarce and has not been explored in much depth. We
present an alternative usage for a DH setup that can measure and monitor the
surface of fluid samples. Based on DH reflectometry, our modelling 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 evaporation of surface layers.
