Single aerosol particle sizing and identification using a coupled-cavity diode laser

A new instrument for aerosol particle size determination and identification by shape is presented. The instrument is based on a diode laser in a coupled cavity. An extinction loss determines the size of a single aerosol particle entering the coupled-cavity diode laser, and a Fourier transformed diffraction image of near-forward scattered light is used for shape and orientation analysis. We describe a model of the coupled-cavity diode laser using light scattering based on Mie theory. This model relates the extinction loss directly to the cross-sectional area of the aerosol particle and shows good agreement with experimental results on aerosol particles and fibers. It is demonstrated that the changes in extinction loss are essentially independent of refractive index of the aerosol particles. The measurable size range of the aerosol particles is 4-170 mu m with an accuracy of +/- 0.5 mu m. The lower limit of the range is set by the extinction loss S/N ratio, the upper limit is given by the laser beam cross-section, and the accuracy is imposed by the oscillations in the extinction efficiency factor. (C) 1999 Elsevier Science B.V. All rights reserved.