Book chapter
Principles of laser anemometry
Laser anemometry is an area characterised by the use of laser light for localised non-perturbing measurements of fluid velocity. The start of what could be called modern laser anemometry goes back to the measurements of Yea and Cummins1. They performed a light scattering experiment on small particles suspended in a fluid pipe flow.
Light scattered in a given direction would exhibit a well-defined Doppler shift. The shift is generally too small to be detected by direct spectral analysis of the optical signal. However, by coherently mixing the scattered light with a reference beam on a photodetector it was possible to obtain a beat signal oscillating with the frequency of the Doppler shift itself.
The light beam illuminating the flow and the reference beam came from the same laser. The reference beam light was frequency shifted by Bragg diffraction in an acousto-optic cell. The principle of frequency shifting in order to overcome the sign ambiguity of the measured velocity did not find widespread use until several years later.
Language: | English |
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Publisher: | Plenum Publishing Corporation |
Year: | 1994 |
Pages: | 85-126 |
ISBN: | 0306448173 , 1489912711 , 1489912738 , 9780306448171 , 9781489912718 and 9781489912732 |
Types: | Book chapter |
DOI: | 10.1007/978-1-4899-1271-8_6 |
Bias Error Doppler Frequency Phase Lock Loop Reference Beam Velocity Fluctuation