“…They were able to measure the velocity of a Ž particle in air. Many scientists followed such as Birchenough and Mason, 1976;Lee and Srinivasan, 1978;Lesinksi et al, 1981;Tsuji et al, 1984;Arastoopour and Yang, 1992;Shao . and Arastoopour, 1995 . Particle-size measurement using laser systems is very chal-Ž .…”