SIMULTANEOUS MEASUREMENT OF PARTICLE SIZE AND VELOCITY BY LASER 2-FOCUS PARTICLE ANALYSER

A laser 2-focus particle analyzer (L2FPA) has been newly developed for measurement of particle size and velocity. A semiconductor laser with wide stripe tip structure is used for the light source. The collimated laser beam is divided into two beams, and is then converged to two foci at the measuring volume. Backscattered light from a particle are led to two photodiodes and are converted to electric pulses. The time-of-flight of a particle and the time-of-scattering of the particle are measured simultaneously by digital counter if the same particle passes through two foci. The particle velocity can be easily calculated by the measured time-of-flight using the known distance between two foci. The particle size is derived from the particle velocity and time-of-scattering using the known focus thickness, because the time-of-scattering is in proportion to the both time-of-flight and particle size. Liquid or solid particles with the diameter range from 2 to 100 micrometers were measured in the air jet by L2FPA and LDV. On the other hand, the particle diameter was checked by microscope photographs. It was shown that the particle size and velocity can be measured simultaneously by the measurements of time-of-flight and time-of-scattering of the particle.