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15 December 2000 Optical mixing in coherent lidar: comparing three schemes
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Proceedings Volume 4087, Applications of Photonic Technology 4; (2000)
Event: 2000 International Conference on Application of Photonic Technology (ICAPT 2000), 2000, Quebec City, Canada
A laser Doppler anemometer for measuring wind speed ahead of wind turbines is under development. The anemometer is based on a CO2 laser. Three schemes for detecting the Doppler frequency of the back-scattered light have been compared with respect to compactness, robustness, signal strength, and cost. The autodyne scheme, where the backscattered light is collected through the same optical path as used for the transmitted beam and re-enters the laser cavity. The Doppler frequency is measured as perturbations of the laser power. The Michelson derived heterodyne system, where the Doppler frequency is measured as a beat frequency between the signal wave and a reference wave in a Michelson-like set-up. In an alternative system for detection by external mixing is the reference wave is established by reflecting a small fraction of the output beam back towards the detector by a partially reflecting window. Due to the response characteristics of the laser, an autodyne laser anemometer, based on a CO2 laser, is found to have an acceptable response only in a very narrow frequency range and is thus not useful the present application. It is decided to build the anemometer by using the alternative heterodyne mixing scheme. This system needs the fewest number of optical components and alignments.
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Rene Skov Hansen, Lars Lading, and Graham M. Miller "Optical mixing in coherent lidar: comparing three schemes", Proc. SPIE 4087, Applications of Photonic Technology 4, (15 December 2000);


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