Effect of the optical numerical aperture on the Doppler spectrum in laser Doppler velocimetry

We have investigated the effect of the optical system design on the characteristics of the Doppler spectrum of a laser Doppler velocimeter, by means of a Monte Carlo simulation model. We show that numerical aperture is one of the parameters that strongly affect the full width at half maximum and signal to noise ratio of the Doppler spectrum. The profile and intensity of the enhanced backscattering of the laser beam from a diffusive rough aluminum disk surface is measured using a range of lenses with different focal lengths and the results are incorporated into the Monte Carlo model.