Holographic Observation of Fine Particles by Two Laser Pulses of Different Wave Length

Abstract

For measuring the size and velocity of fine particles the double pulsed laser holographic method is a useful technique, but this is not convenient for the system of high particle number density, because of the difficulty in identification of moving particles on a double exposure hologram. In order to remove this difficulty, we have developed a new technique employing the two pulsed lasers of different wave length.The two lasers are set in the same optical axis passing through the observation section, and fired at an interval of few milli∼micro seconds depending on the particle velocity in the experimental objects. The two output beams with holographic information of the object particles are separated into two camera boxes by a half mirror and two interference filters, and then the holograms of the particle system at different instants are recorded on two films separately. These two holograms are superimposed each other, and the distances of particle movements are measured microscopically. From the distance and pulse interval, the velocity distribution of particles are obtained. This new technique was applied successfully to observe the disintegration mechanism of liquid spray.