Simultaneous measurement of localized diffusion and flow using optical coherence tomography

TL;DR

This paper introduces a method using optical coherence tomography to simultaneously measure local diffusion coefficients and flow velocities, demonstrating how beam waist affects sensitivity and measurement precision.

Contribution

It presents a novel OCT-based technique for concurrent localized diffusion and flow measurement, analyzing the influence of beam waist on sensitivity and accuracy.

Findings

Smaller beam waist improves flow velocity sensitivity.

Flow decay depends only on beam waist, not sample position.

Reliable estimation of diffusion and flow in a single measurement.

Abstract

We report on the simultaneous and localized measurements of the diffusion coefficient and flow velocity based on the normalized autocorrelation function using optical coherence tomography (OCT). Our results on a flowing solution of polystyrene spheres show that the flow velocity and the diffusion coefficient can be reliably estimated in a regime determined by the sample diffusivity, the local flow velocity, and the Gaussian beam waist. We experimentally show that a smaller beam waist results in an improvement of the velocity sensitivity at cost of the precision and accuracy of the estimation of the diffusion coefficient. Further, we show that the decay of the OCT autocorrelation due to flow depends only on the Gaussian beam waist irrespective of the sample position with respect to the focus position.