Low power gas lasers are nearly ideal light sources for particle size spectrometers. Particle size spectrometers involving imaging and light scattering have proven most satisfactory and are described in detail. The imaging spectrometers use 2 - 5 mW He-Ne lasers and a photodiode array to size and provide particle shape information on particles 1 - 10,000 μm diameter. Airborne spectrometers designed for hydrometeor measurements have 128 MHz data rate capabilities and provide full data compression. The light scattering spectrometers developed use 1 - 2 mW He-Ne lasers in both open and closed cavity sensing configurations. These instruments typically size particles with diameters less than 0.1 μm to greater than 30 μm. Methods of combining an imaging system with the light scattering methods to define the sample volume are detailed. Some possible advantages of short and multiwavelength lasers are discussed.
Robert G. Knollenberg,
"The Use Of Low Power Lasers In Particle Size Spectrometry", Proc. SPIE 0092, Practical Applications of Low Power Lasers, (18 January 1977); doi: 10.1117/12.955100; https://doi.org/10.1117/12.955100