Sizing of inhomogeneous particles by a differential laser Doppler anemometer

A particle moving across the interference pattern of two intersecting laser beams scatters the incident light with a temporal variation that enables the calculation of particle velocity. This idea was realized in laser Doppler anemometry (LDA). By recording the light scattering pattern with a fast line scan sensor, the spatial modulation of the signal is also detected. This yields, in addition to particle velocity, information about the size and morphology of the particle. This is the working principle of a new measuring device presented in this paper, the differential laser Doppler anemometer (DLDA). The theoretical background, principle of data evaluation and first experimental results of water and emulsion droplets and of glass beads are described.