diffraction velocimeter

diffraction velocimeter [di′frak·shən ‚vel·ə′sim·əd·ər]

(optics)

A velocity-measuring instrument that uses a continuous-wave laser to send a beam of coherent light at objects moving at right angles to the beam; the needlelike diffraction lobes reflected by the moving objects sweep past the optical grating in the receiver, thereby generating in a photomultiplier a series of impulses from which velocity can be determined and read out. Also known as optical diffraction velocimeter.