We quantify the precision and bias of dynamic light scattering optical coherence tomography (DLS-OCT) measurements of the diffusion coefficient and flow speed for first and second-order normalized autocovariance functions. For both diffusion and flow the measurement precision and accuracy are severely limited by correlations between the errors in the normalized autocovariance function. We demonstrate a method of mixing statistically independent normalized autocovariance functions at every time delay for removing these correlations. The mixing method reduces the uncertainty in the obtained parameters by a factor of two but has no effect on the standard error of the mean. We find that the precision in DLS-OCT is identical for different averaging techniques, but that the lowest bias is obtained by averaging the measured correlation functions before fitting the model parameters. With our correlation mixing method it is possible to quantify the precision in DLS-OCT and verify whether the Cramer-Rao bound is reached.
We demonstrated the application of wavenumber-dependent DLS-OCT to measure both collective and self-diffusion coefficients in concentrated silica suspensions. Depending on the sample polydispersity, we successfully measured either long-time collective or long-time self-diffusion over a broad q-range using our custom-built OCT system. The measured collective diffusion coefficient shows excellent agreement with hard-sphere theory, providing further evidence for the dynamic scaling property. It also serves as an effective tool for accurately determining particle sizes in concentrated suspensions. We found the decoupling approximation to be highly effective in describing the first-order normalized autocovariance functions in both monodisperse and relatively polydisperse samples.
We show number fluctuations dynamic light scattering Optical Coherence Tomography (OCT) for measuring extremely slow, sub-diffusion flows of dilute particle suspensions. Our method removes the minimum measurable velocity limitation of conventional correlation-based or phase-resolved Doppler OCT, set by flowing particles’ Brownian motion. Our technique works for any Doppler angle, is applicable to 2D flow imaging with scanning OCT systems and can be used to determine concentration of particles under flow.
We show scanning dynamic light scattering optical coherence tomography (OCT) omnidirectional flow measurements. Our method improves the velocity measurement limit over conventional correlation-based or phaseresolved Doppler OCT by more than a factor of 2. Our technique is applicable without a-priori knowledge of the flow geometry as our method works both for non-zero Doppler angle and non-ideal scan alignment. In addition, the method improves the particle diffusion coefficient estimation for particles under flow.
We show number fluctuations dynamic light scattering optical coherence tomography (OCT) for measuring extremely slow, sub-diffusion flows of dilute particle suspensions. Our method removes the minimum measurable velocity limitation of conventional correlation-based or phase-resolved Doppler OCT, set by flowing particles’ Brownian motion. Our technique works for any Doppler angle, is applicable to 2D flow imaging with scanning OCT systems and can be used to determine concentration of particles under flow.
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