Further Particle Sizing Methods Based on the Laser Doppler Technique

The distinguishing factor common to techniques discussed in this section is that not only particle size of every detected particle is measured, but also velocity. This classifies these techniques as single particle counting techniques and allows both particle flux density (number of particles per unit time and area) and concentration to be computed (Black et al. 1996). This is in contrast to diffraction-based particle sizers, which make an estimate of the size distribution over an ensemble of particles without knowing the contribution of any individual particle or its velocity. One of the techniques discussed in this chapter (Shadow Doppler Velocimetry, SDV) is no longer restricted to spherical particles and several of the techniques (amplitude-based) require calibration.