LASER DOPPLER VELOCIMETER WITH EDGE FILTER DEMODULATION

摘要

The invention relates to a velocimeter and a method for determining the speed of a target. The velocimeter comprises a laser source comprising a laser cavity for producing a continuous-wave laser beam, a light detector, and means for directing a first portion of the laser beam to a moving target outside the velocimeter for producing scattered light from the target, the scattered light exhibiting a Doppler shift corresponding to the speed of the moving target. Further, the velocimeter comprises means for guiding scattered light back to the laser cavity for providing frequency-modulation of the laser beam through perturbance in the laser source, and means for guiding a second portion of the laser beam to the light detector. According to the invention, there is further provided an optical edge filter adapted to demodulate said frequency-modulated laser beam before guiding to the light detector and wherein said laser source is adapted to produce laser light at a wavelength corresponding to the wavelength of the edge of the optical edge filter. The invention improves the sensitivity of self-mixing velocimeters.