Abstract
Digital in-line holography is used to visualize particle motion within a cylindrical micropipe. Analytical expression of the intensity distribution recorded in the CCD sensor plane is derived using the generalized Huygens-Fresnel integral associated with the ABCD matrices formalism. Holograms obtained in a 100microm in diameter micropipe are then reconstructed using fractional Fourier transformation. Astigmatism brought by the cylindrical micropipe is finally used to select a three dimensional region of interest in the microflow and thus to improve axial localization of objects located within a micropipe. Experimental results are presented and a short movie showing particle motion within a micropipe is given.
Highlights
Digital holography is a recognized technique for flow characterization
By modifying the experimental set-up, we show that, using the experimental method proposed in Ref [20], a three-dimensional region of interest (ROI) can be selected and studied in a micropipe flow
Particle hologram recorded according to this configuration is presented Fig. 9(a)
Summary
Digital holography is a recognized technique for flow characterization. As a matter of fact, domains such as fluid mechanics or biological imaging benefit from the three dimensional information contained by one hologram [1,2,3]. Microfluidics aims to manipulate small amounts of liquid within microchannels with dimensions of few hundreds micrometers, and find many applications in electronic component cooling [7] or document printing [8]. Imaging through these channels is a challenging problem [9]. Due to their cylindrical geometry, microchannels introduce aberrations such as astigmatism in the imaging system [10]. These unwanted effects make it difficult to retrieve information about seeding particles located in the channel. The authors succeeded in obtaining three-dimensional velocity fields in various types of microfluidics devices without astigmatism [11,12,13,14,15]
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