Directional Laser Doppler Velocimeter

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Abstract
A directional laser doppler velocimeter for localized directional measurements of fluid flow is described Doppler-shifted radiation is scattered and received from small particles in the fluid. The frequency shift is proportional to the velocity of the scatterer and can be detected by heterodyning the scattered signal with an appropriate reference. Directional sensitivity is achieved by shifting the frequency of the reference laser beam, using an acoustical diffraction cell. Results of steady and time-varying flow velocity measurements in a perturbed circular flow section are presented.