A unified analysis on laser Doppler velocimeters

Using the theory of optical mixing spectroscopy a unified analysis on various optical arrangements of laser Doppler velocimeter, such as local-oscillator heterodyne differential heterodyne and symmetric heterodyne are given. Their theory of operation, signal-to-noise ratio, spectrum broadening and relative merit are discussed. It is found that the differential heterodyne arrangement is superior to all other arrangements, such as laminar flow or rotating disc, in the measurement of uniform velocity, whilst for turbulent flow measurements the relative merit depends on the particle size, particle concentration, dimension of scattering region, etc.