Abstract
Phase Doppler anemometry (PDA) is one of the useful and reliable optical methods for sizing small spherical particles. However, this method is sensitive to the Gaussian beam effect which can cause phase fluctuation and therefore erroneous measurements. This paper theoretically studies the mechanism of the phase fluctuation. A detailed and systematic estimation of the phase fluctuation is performed by using geometrical optics. The validity of this estimation is confirmed by numerical simulations based on the generalized Lorenz-Mie theory. Moreover, we discuss the optimum measuring conditions which can minimize the phase fluctuation.
