LDVmouse

two-axis velocimetry using the Philips PLN20** series of laser-Doppler motion sensors
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See Zaron, "Laser Doppler velocimetry of a flowing soap-water film using a modified computer mouse." American Journal of Physics, 84(10):810--813, 2016.

What you will find here:

The measurement principle of the PLN20** devices requires the scatterers to lie in a well-defined plane. Because of this, I was never able to use the device to measure velocity in water, and I am no longer investigating it. As demonstrated in the manuscript, though, it is completely viable for measuring velocity in the plane of a flowing water film. The primarily limitation for quantitative work is the difficulty of precisely the distance between the sensor and the flow plane.