Laserdiffraktionens

Laserdiffraktionens, the Swedish term for laser diffraction, denotes a family of measurement techniques used to determine particle size distributions by analyzing the angular distribution of light scattered by particles when illuminated with a laser. The method covers a wide size range and is applied to both liquids and dry powders.

Principles: When a laser beam passes through a dispersed sample, particles scatter light at angles that depend on their size and refractive index. The angular scattering pattern relates to the particle size distribution through scattering theories, most commonly Mie theory for spherical particles, or approximations for larger or non-spherical particles. The measured pattern is converted into a size distribution using mathematical inversion algorithms.

Instrumentation: A laser diffractor consists of a laser source, a dispersion system (for liquids: a sample cell; for dry powders: a disperser), and a detector array that records scattered light over a range of angles. Data processing yields a cumulative or differential size distribution. The typical measurement range is from about 0.1 μm to several millimeters, depending on setup and refractive index inputs. Calibration with standard particles is common.

Considerations: The method assumes particles are spherical or uses models for non-spherical shapes; results can be influenced by particle refractive index, concentration, and agglomeration. Proper dispersion and avoidance of multiple scattering are important.

Applications: Widely used in pharmaceuticals, coatings, polymers, food, cosmetics, and environmental analyses for process monitoring and quality control.