The electromagnetic scattering problem of Laser-Doppler Anemometry. Part II: Particle investigation

The second part of this review concentrates on the situation where the moving particles that scatter light are themselves an essential part of the flow under investigation. In order to obtain information also on their nature und their shape, their quantitative characterization by light scattering is needed. This characterization is codified in the magnitude which describes scattering, the scattering amplitude. It becomes transparent for very small and very large particles, because their scattering mechanisms can be interpreted in terms of electromagnetic multipoles and of geometrical optics, respectively. Scatterers of the simplest composition and shape, homogeneous spheres, are considered in detail; they are characterized optically by their radius and index of refraction. It is shown that phase measurements of the modulated scattering signal (phase Doppler anemometry, PDA) can provide, with suitably located detectors, information on these quantities.