High-speed axial-scanning wide-field microscopy for volumetric particle tracking velocimetry

The ability to understand and visualize complex flow structures in microfluidic and biological systems relies heavily on the resolving power of three-dimensional (3D) particle velocimetry techniques. We propose a simple technique for acquiring volumetric particle information with the potential for microsecond time resolution. By utilizing a fast varifocal lens in a modified wide-field microscope, we capture both volumetric and planar information with microsecond time resolution. The technique is demonstrated by tracking particle motions in the complex, three-dimensional flow in a high Reynolds number laminar flow at a branching arrow-shaped junction.