Abstract
We present a way to measure the positions and instantaneous velocities of micrometer-scale colloidal spheres using a single holographic snapshot obtained through in-line holographic video microscopy. This method builds on previous quantitative analyses of colloidal holograms by accounting for blurring that occurs as a sphere moves during the camera's exposure time. The angular variance of a blurred hologram's radial intensity profile yields both the magnitude and direction of a sphere's in-plane velocity. At sufficiently low speeds, the same hologram also can be used to characterize other properties, such as the sphere's radius and refractive index.
Highlights
Particle image velocimetry (PIV) is widely used to map fluid flows at scales ranging from a few micrometers to many meters [1, 2]
We describe how to extract this dynamical information from a single holographic snapshot, taking advantage of blurring due to motion during the camera’s exposure time
To assess the effectiveness of angular moment analysis for snapshot holographic velocimetry, we use Eqs. (4) through (7) to analyze simulated holograms blurred according to Eq (2) with I(r,t) = I(r − vt)
Summary
Particle image velocimetry (PIV) is widely used to map fluid flows at scales ranging from a few micrometers to many meters [1, 2]. Typical implementations measure a tracer particle’s velocity by comparing its position in a sequence of images separated by known time intervals. We describe how to extract this dynamical information from a single holographic snapshot, taking advantage of blurring due to motion during the camera’s exposure time. The blurred holographic image still can be used to measure each particle’s threedimensional position and properties with high resolution [3, 4, 5]
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