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.