Fraunhofer light scattering determine particle size

Other techniques also based on mass are sedimentation and light scattering/diffraction. The most popular technique offered by several companies is Fraunhofer diffraction. In each case, including sieves, there will be some difficulty in measuring small particles in the presence of larger particles. This will manifest itself in poor estimation of the small size population density, a shortcoming that will become more obvious when nucleation rates are determined from crystal size distribution measurements. 

A particle size analyzer determines the particle size distribution of powders either dry or dispersed in solvent by laser light scattering based on the Fraunhofer scattering theory. This type of equipment has an optical bench whose combined dynamic range is nominally 0.7-2000 pm. The instrument calculates mean diameters and distribution data. An interfaced computer generates sample histograms. This technique has been applied to the study of particle size and particle size distributions for polymer powders and polymer suspensions in a variety of solvents. 

Particle sizing instruments can be categorized by the method qjplied to determine a size distribution. Integral optical methods like Fraunhofer Diffraction or Dynamic Light Scattering require extensive mathematics to extract the particle size distribution from samples. The general shape of this distribution is ordinarily assumed and a few parameters of this assumed distribution are adjusted to represent features of the data. Because of these restrictions, integral optical methods are not able to resolve all fine details of a particle size distribution. 

---