A laser technique for the measurement of aerosols

Abstract

The paper describes the use of a continuous-wave helium-neon laser to measure the surface area of small concentrations (< 3000 particles per cm3) of dust particles, of size less than 5 μm, suspended in air. The suspension is passed through a size-selector to remove dust particles greater than 5 μm in size and then into a chamber between one of the laser mirrors and the end of the laser tube. Scattering and absorption of radiation from the cavity by the dust particles causes a change in the amount of radiation reflected back into the laser tube, which in turn produces a reduction in the intensity of the output beam. The relationship between the surface-area concentration of the airborne dust and the change in the output intensity is derived, and experiments with an instrument of this type are described and discussed.