Method and apparatus for measuring physical values of light scattering moving particles with a laser Doppler fluid velocimeter

摘要

The particle characteristics measurement has light for at least one pair of coherent beams superimposed at a given measuring point within the measuring volume, after passage of at least one of the beams through a phase modulator, with detection of light dispersed from particles within the measuring volume and analysis of the dispersed light w.r.t. its Doppler shift. The phase modulator is controlled by a pair of sinusoidal control signals of different frequency and amplitude. The receiver (4) for the dispersed light is coupled to a bandpass filter (5) with a filter frequency which is a common multiple of both the control signal frequencies. The filter has a bandwidth corresponding to the max. expected Doppler shift, the control signal amplitudes selected to provide for suppression of one sideband.