Single-particle laser Doppler anemometry at 1.55 mu m

We demonstrate the successful operation of a cw laser Doppler wind sensor a t a wavelength of 1.55 mum. At longer ranges (>100 m) the signal conforms c losely to complex Gaussian statistics, consistent with the incoherent addit ion of contributions from a large number of scattering aerosols. As the ran ge is reduced, the probe volume rapidly diminishes and the signal statistic s are dramatically modified. At the shortest ranges (<8 m) the signal becom es dominated by short bursts, each originating from a single particle withi n the measurement volume. These single-particle events can have a very high signal-to-noise ratio (SNR) because (1) the signal becomes concentrated wi thin a small time window and (2) its bandwidth is much reduced compared wit h multiparticle detection. Examples of wind-signal statistics at different ranges and for a variety of atmospheric backscatter conditions are presente d. Results show that single-particle-scattering events play a significant r ole even to ranges of <similar to>50 m, leading to results inconsistent wit h complex Gaussian statistics. The potential is assessed for a low-power la ser Doppler wind sensor that exploits the SNR enhancement obtained with sin gle-particle detection. OCIS codes: 120.0280, 280.3400.