Abstract
We report on localized measurement of the longitudinal and transverse flow velocities in a colloidal suspension using optical coherence tomography. We present a model for the path-length resolved autocorrelation function including diffusion and flow, which we experimentally verify. For flow that is not perpendicular to the incident beam, the longitudinal velocity gradient over the coherence gate causes additional decorrelation, which is described by our model. We demonstrate simultaneous imaging of sample morphology and longitudinal and transverse flow at micrometer scale in a single measurement.
Highlights
Modern experiments to study mass transport phenomena in complex rheological systems such as microfluidics [1], polymer solutions [2], biofilms [3], blood microcirculation [4], and blood [5,6] demand spatially and time resolved probing of concentration fields, pressure gradients, velocity profiles, wall shear stress, and diffusion coefficients
We present a theory for the path-length resolved Optical coherence tomography (OCT) signal and its normalized autocorrelation function for the case of arbitrarily oriented flow in the presence of diffusion
The presented method can be used to determine with micrometer spatial resolution both the diffusion coefficient and the flow velocity from the OCT autocorrelation function simultaneously with the sample morphology
Summary
Modern experiments to study mass transport phenomena in complex rheological systems such as microfluidics [1], polymer solutions [2], biofilms [3], blood microcirculation [4], and blood [5,6] demand spatially and time resolved probing of concentration fields, pressure gradients, velocity profiles, wall shear stress, and diffusion coefficients. Optical techniques use a (coherent) light source to illuminate the sample and detect the fluctuations of the scattered light. Among conventionally used optical techniques are laser Doppler flowmetry (LDF) [7], laser speckle velocimetry (LSV) [8], and particle image velocimetry (PIV) [9]. In LDF, scattered light interferes with a local oscillator, and the intensity fluctuations of the detected light are related to the Doppler shift generated by flow in the sample. In LSV, the velocity of the scatterers is quantified by the intensity fluctuations that originate from the movement of the scatterers through the probing field. In LDF, LSV, and PIV the exact path-length distribution of the scattered light is unknown, making it impossible to quantify the velocity distribution deep inside the sample, thereby providing only volumetrically averaged information of the sample dynamics
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