Abstract

Laser light-scattering interferometry or the Phase/Doppler technique has been used in a wide variety of particle-sizing applications, including diagnostic studies of combustion processes, nozzle sprays, and droplets in the atmosphere [1-5]. In this technique, radiation from a laser is split into two or four beams, the beams are focused and crossed over a very small measurement volume. As the droplets or particles pass through the intersection of the laser beams, scattering occurs and temporal and spatial frequencies of the droplets or particles are recorded to obtain droplet velocities, diameter, and concentration. The principle behind this measurement technique is similar to that for the laser Doppler velocimetery, except that scattered light is detected at large angle using two or more photodetectors. If a two-beam system (1D or one-component system) is used, particle size (0.5 to 10,000 μm) and particle velocities can be simultaneously measured in one direction on a microsecond time scale (down to 0.8 μs). With the two-component system (2D system), these parameters are assessed in two directions. In short, a Phase/Doppler instrument allows measurements of temporal and spatial information for a particle field. In contrast, the droplet size measured with laser Fraunhofer diffraction [6,7] represents a line-of-sight integral measurement, and droplet velocity information cannot be obtained.

© 1994 Optical Society of America