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Laser Doppler velocimetry
Laser Doppler velocimetry (LDV), also known as laser Doppler anemometry (LDA), is the technique of using the Doppler shift in a laser beam to measure the velocity in transparent or semi-transparent fluid flows, or the linear or vibratory motion of opaque, reflecting, surfaces. The measurement with LDA is absolute, linear with velocity and requires no pre-calibration.
==Technology origin==
With the development of the helium–neon laser (He-Ne) at the Bell Telephone Laboratories in 1962, the optics community had available a source of continuous wave electromagnetic radiation highly concentrated at a wavelength of 632.8 nanometers (nm), in the red portion of the visible spectrum.〔White, A. D., and J. D. Rigden, "Continuous Gas Maser Operation in the Visible". ''Proc IRE'', vol. 50, p. 1697: July 1962, p. 1697. .〕 It was soon shown fluid flow measurement could be made from the Doppler effect on a He-Ne beam scattered by very small polystyrene spheres entrained in the fluid.
At the Research Laboratories of Brown Engineering Company (later Teledyne Brown Engineering), this phenomenon was used in developing the first laser Doppler flowmeter using heterodyne signal processing.
The instrument was soon called the laser Doppler velocimeter (LDV) and the technique laser Doppler velocimetry, also abbreviated LDV. Another application name is laser Doppler anemometry (LDA). Early LDV applications ranged from measuring and mapping the exhaust from rocket engines with speeds up to 1000 m/s to determining flow in a near-surface blood artery. A variety of similar instruments were developed for solid-surface monitoring, with applications ranging from measuring product speeds in production lines of paper and steel mills, to measuring vibration frequency and amplitude of surfaces.
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