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 t he calculation of particle velocity. This idea was realized in laser Dopple r anemometry (LDA). By recording the light scattering pattern with a fast l ine scan sensor, the spatial modulation of the signal is also detected. Thi s 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 p aper, the differential laser Doppler anemometer (DLDA). The theoretical bac kground, principle of data evaluation and first experimental results of wat er and emulsion droplets and of glass beads are described.