Abstract
Correlation spectroscopy is an analytical technique that can identify the residence time of reflective or fluorescent particles in a measurement spot, allowing particle velocity or diffusion to be inferred. We show that the technique can be applied to data measured with a time-domain terahertz sensor. The speed of reflectors such as silica ballotini or bubbles can thus be measured in fluid samples. Time-domain terahertz sensors can therefore be used, for the first time, to measure rheological properties of optically opaque fluids that contain entrained reflectors, such as polyethylene beads.
Highlights
We show in this Letter that the method of correlation spectroscopy [3], developed for confocal fluorescence microscopy, can be applied to data from a time-domain terahertz sensor to measure particle velocity as a spot measurement, and to measure a onedimensional velocity profile of a fluid
In fluorescence correlation spectroscopy (FCS), the fluorescence intensity from a static observation volume within a fluid specimen is recorded for a period of typically milliseconds or seconds
The durations of the “bumps” in the fluorescence signal depend on the speeds of the fluorophores and the size of the observation volume
Summary
We show in this Letter that the method of correlation spectroscopy [3], developed for confocal fluorescence microscopy, can be applied to data from a time-domain terahertz sensor to measure particle velocity as a spot measurement, and to measure a onedimensional velocity profile of a fluid. To perform terahertz correlation velocimetry as a spot measurement, silica ballotini of diameters 212, 425, 600, and 850 μm were separately dispersed into 1 ml volumes of the paraffin oil so that the particles comprised 1% vol of the fluid.
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