Abstract

A novel heterodyne differential Doppler technique for the simultaneous directional measurement of two velocity components of fluid flows is presented. The technique is based on the generation of different carrier frequencies, each for one velocity component. The realized differential laser Doppler velocimeter employs a frequency modulated Nd:YAG miniature ring laser coupled into fiber-optics for an alignment insensitive splitting, transfering and delaying of the laser beams. The laser frequency modulation in conjunction with different optical delays generates the carrier frequencies without additional frequency shift elements, so that a simplified velocimeter can be realized.

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