Optical EngineeringMethod for small particle detection by laser
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A method for the detection of small particles by a laser is presented. This method is based on the interaction of the particle with the field in the external cavity of the laser. The radiation scattered back by the moving particle into the laser resonator interferes with the field inside and causes changes in the pump current. The experimental device consists of a single-mode diode or gas laser with an external cavity. Information concerning the number, velocity and size of particles can be derived by processing the laser pump current pulses. This method is capable of detecting the movement of a single micrometer-diameter particle.