Digital in-line holography for near field observation of liquid-liquid flows under astigmatic conditions
Abstract
Several processes used in nuclear research and industry
are based on liquid-liquid extraction. This method is
designed for selective separation of products in a mixture.
As the transfer occurs at the contact surface between
both phases, the characterization of the dispersed phase of
the emulsion (size distribution of droplets, shape, etc.) is
fundamental. Numerous imaging techniques can be used
to measure, but one of them, digital holography (DH) is
particularly relevant as it determines simultaneously the
size, shape and 3D positions of particles using a single
camera. Because the droplets are millimeter size, a nearfield diffraction regime is observed and adapted numerical
solutions are required. In a previous work [1], an effective
focusing method has been validated on an experimental
cuboid-shape setup designed to produce droplets of
known diameter and velocity as well as an unknown
polydisperse droplet population. However, the standard
shapes of liquid-liquid extraction apparatus are
cylindrical, inducing a strong astigmatism and preventing
the direct use of classical focusing methods.
In this communication, we proposed a survey of two
approaches, based respectively on Generalized Huygens-Fresnel
Transform (GHFT) and Fractional Fourier
Transform (FrFT), which allows overpassing this issue.
Using these tools induce a supplementary quadratic phase
term, which must be corrected in order to use automatic
focalisation methods.
Origin : Files produced by the author(s)
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