LIGHT FREQUENCY CHANGE DETECTING METHOD AND APPARATUS

摘要

A method and apparatus for detecting a frequency change of a light modulates the scattered light from the object of measurement using an acousto-optic modulator or the like, heterodyne-detects the scattered light after modulation to provide an electrical signal having a frequency (fd-fm) which is the difference between the Doppler frequency fd and the modulation frequency fm, passes this electrical signal to a filter while changing the modulation frequency fm, and obtains the modulation frequency fm at which the signal voltage is the largest or the smallest, that is, the Doppler frequency fd.