Ghost particle velocimetry: accurate 3D flow visualization using standard lab equipment.
We describe and test a new approach to particle velocimetry, based on imaging and cross correlating the scattering speckle pattern generated on a near-field plane by flowing tracers with a size far below the diffraction limit, which allows reconstructing the velocity pattern in microfluidic channels without perturbing the flow. As a matter of fact, adding tracers is not even strictly required, provided that the sample displays sufficiently refractive-index fluctuations. For instance, phase separation in liquid mixtures in the presence of shear is suitable to be directly investigated by this "ghost particle velocimetry" technique, which just requires a microscope with standard lamp illumination equipped with a low-cost digital camera. As a further bonus, the peculiar spatial coherence properties of the illuminating source, which displays a finite longitudinal coherence length, allows for a 3D reconstruction of the profile with a resolution of few tenths of microns and makes the technique suitable to investigate turbid samples with negligible multiple scattering effects.
Department of Chemistry (CMIC), Politecnico di Milano, via Ponzio 34/3, 20133 Milano, Italy. stefano.buzzaccaro@polimi.it
Stefano
S
Buzzaccaro
Eleonora
E
Secchi
Roberto
R
Piazza