A new method for recording single-shot two-scales in-line holograms: Application to the visualization of a stretched viscoelastic fluid

In many applications of fluid mechanics, it is necessary to simultaneously study large fields of view and zoom-in for specific areas of the flow. This is especially the case for the dynamics of viscoelastic filaments in which both micrometric and centimetric scales are involved. For this purpose, we develop an original in-line holographic configuration that allows the simultaneous recording of two views of the same scene at different scales. We then test the setup on a viscoelastic filament under controlled stretching. We show that this method enables us to reconstruct a pair of images at two distinct spatial resolutions. In this example, the entire filament and a small zone of beads along the filament can be imaged at the same time. We discuss a critical analysis of the advantages and limitations of this configuration.