Simultaneous and localized measurement of diffusion and flow using optical coherence tomography

Area of Science:

• Biophotonics
• Fluid Dynamics
• Optical Measurement Techniques

Background:

• Accurate characterization of microfluidic environments is crucial for various scientific disciplines.
• Simultaneous measurement of diffusion and flow dynamics presents a significant challenge in complex fluids.

Purpose of the Study:

• To develop and validate a method for simultaneous, localized measurement of diffusion coefficient and flow velocity.
• To investigate the impact of optical parameters, specifically Gaussian beam waist, on measurement accuracy and sensitivity.

Main Methods:

• Utilized a normalized autocorrelation function derived from Optical Coherence Tomography (OCT) data.
• Employed a flowing suspension of polystyrene spheres as a model system.
• Experimentally varied the Gaussian beam waist to assess its influence on measurements.

Main Results:

• Demonstrated reliable estimation of flow velocity and diffusion coefficient within a specific operational regime.
• Showcased that a smaller beam waist enhances velocity sensitivity while decreasing diffusion coefficient precision.
• Confirmed that OCT autocorrelation function decay due to flow is solely dependent on beam waist, independent of sample focus position.

Conclusions:

• OCT-based autocorrelation analysis provides a robust method for simultaneous flow and diffusion characterization.
• Optimizing Gaussian beam waist is critical for balancing velocity and diffusion measurement performance.
• The findings offer a valuable tool for studying dynamic processes in microfluidic and biological systems.