Unidirectional phase-Doppler method for particle-size measurements

We propose what we believe to be a novel unidirectional phase-Doppler method for sizing moving spherical particles on the basis of the phase difference of two polarized Doppler beat signals in a single scattering direction. Light scattered by a moving particle is divided into two rays, which are detected with different polarization angles to transmit dominantly reflected or refracted rays. The phase difference between two signals is linearly proportional to the particle diameter with a given particle refractive index and geometrical parameters of the optical system. To explore the optimum polarization condition, we numerically investigated the phase-diameter properties in relation to polarization angles by using the geometrical optics approximation and generalized Lorenz-Mie theory. We also performed experiments with polystyrene and glass particles to verify the usefulness of the proposed method.