laserdiffractionin

Laser diffraction is a particle sizing technique that determines the size distribution of dispersed particles by analyzing the pattern of light scattered from a sample when illuminated with a laser. The angular distribution of scattered light depends on particle size: larger particles preferentially scatter light at small angles, while smaller particles create broader scattering patterns. In practice, the scattering pattern is interpreted with diffraction theory, typically using Mie theory for a full range of sizes and refractive indices, or Fraunhofer approximations for larger particles or simpler cases.

In a typical instrument, a narrow laser beam passes through a sample contained in a cuvette or flow cell. Detectors arranged around the sample measure the intensity of scattered light at many angles. The recorded angular distribution is mathematically inverted to yield a particle size distribution, usually expressed as volume or number percent across size bins. The computation requires knowledge of the particle refractive index and the suspending medium, and it often reports statistics such as D10, D50, and D90, which describe percentiles of the distribution.

Applications of laser diffraction span pharmaceuticals, food and beverage, cosmetics, minerals, and environmental monitoring. It is used for quality control of powders, slurries, and aerosols, as well as for process monitoring and formulation development. Limitations include reliance on particle sphericity assumptions in the modeling, sensitivity to multiple scattering at high concentrations, and the need for proper dispersion to avoid aggregation.