Detection of airborne particles using optical extinction measurements.

A method for obtaining real-time size distributions of airborne particles is discussed, and experimental sensitivity measurements are presented. By detecting the transmitted power of a low noise He-Ne laser, the optical extinction cross sections of individual particles are measured as they flow through the focused beam. Calculations for various absorbing materials show the extinction cross sections are from one to more than two orders of magnitude larger than their scattering cross sections for particle diameters in the 0.02-0.2-microm range. Sensitivity calculations and measurements indicate extinction cross sections down to 2 x 10(-12) cm (2) can be detected. This suggests absorbing particles as small as 0.04-microm diam can be measured using this technique.