Combined dual scatter, local oscillator laser doppler velocimeter

摘要

A laser Doppler velocimeter is described which is capable of effectively measuring two different velocity components of a fluid simultaneously. Such a velocimeter includes a pair of coherent beams of laser light which are focused to an intersection point through which flow particles within the fluid whose velocity is to be measured. Both beams are plane polarized with the plane of polarization of one being rotated normally with respect to the other, with the result that the scattered radiation is separable into two different beams respectively corresponding to the two incident beams. Such scattered radiation is Doppler shifted by the moving particles and is collected for conventionally providing a measurement of the velocity of any particle flowing through the intersection point on a path which is generally transverse thereto. Moreover, the wavelength of the light scattered by the particles from one of the beams is compared to the wavelength of such beam prior to it being Doppler shifted by the moving particles. This comparison provides a measurement of another component of the particle velocity, which measurement can be combined with the first measurement to provide a resultant velocity in a two-dimensional reference frame.