Light scattering measurements of particle distributions

Specially designed Fraunhofer plane masks are described for passing diffracted flux in proportion to the second, third, and fourth power of the radius of spherical particles. For a distribution of particles, the total volume of the particles can be monitored using the third power mask to produce a signal proportional to the sum of the cubes of the particle radii. Ratios of signals passing through the second, third, and fourth power masks provide statistical parameters of the distribution, such as the volume mean radius, the area mean radius, and the area standard deviation.