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Proceedings Paper

Optical mixing in coherent lidar: comparing three schemes
Author(s): Rene Skov Hansen; Lars Lading; Graham M. Miller
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Paper Abstract

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.

Paper Details

Date Published: 15 December 2000
PDF: 5 pages
Proc. SPIE 4087, Applications of Photonic Technology 4, (15 December 2000); doi: 10.1117/12.406338
Show Author Affiliations
Rene Skov Hansen, Risoe National Lab. (Denmark)
Lars Lading, Sensor Technology Ctr. (Denmark)
Graham M. Miller, Ferranti Photonics Ltd. (United Kingdom)


Published in SPIE Proceedings Vol. 4087:
Applications of Photonic Technology 4
Roger A. Lessard; George A. Lampropoulos, Editor(s)

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