Measurement of fluid diffusion coefficient based on bidirectional scanning in optical coherence tomography

Although dynamic light scattering optical coherence tomography (DLS-OCT) performs well in the measurement of the diffusion coefficient within stationary or low-speed fluid, significant deviation occurs for high-speed fluid since the translation motion dominates the decay process. In this paper, we propose a method for measuring the fluid diffusion coefficient based on bidirectional scanning OCT. Two autocovariance functions corresponding to forward and backward scanning are exploited for the construction of a synthetic autocovariance function with minimum decay, which is beneficial for determining the diffusion coefficient even within high-speed fluid. The feasibility of the method was validated in scattering fluid with medium and high flow rates. Simultaneous measurements of the diffusion coefficients and vector flow velocities were further conducted in fluid within a curved pipe, demonstrating that the proposed method can achieve effective and reliable characterization of a complex fluid field.