Abstract
This paper describes the use of a low-power gas laser as a source of radiation for a Doppler radar working at optical frequencies. The laser beam is focused on to a moving target and the light back-scattered from the target is photo-mixed with a reference signal to give the Doppler difference frequency. Doppler tracking techniques are used to establish the target speed. The system has been applied to the measurement of speed of aluminium extrusions, hot steel, plastic strip, nylon thread, paper, and many other materials. The reliability of the laser Doppler system in an industrial environment has been shown by the fact that it has now been in continuous operation on an aluminium extrusion press for over seven months without requiring any attention or servicing.
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