Laser diffraction analysis or laser diffraction spectroscopy is a scientific technique which utilizes properties of the diffraction

Diffraction

Diffraction refers to various phenomena which occur when a wave encounters an obstacle. Italian scientist Francesco Maria Grimaldi coined the word "diffraction" and was the first to record accurate observations of the phenomenon in 1665...

 patterns of a laser beam passed through a substance, to measure the size of its particles. Laser diffraction analysis is based on the theory of Fraunhofer diffraction

Fraunhofer diffraction

In optics, the Fraunhofer diffraction equation is used to model the diffraction of waves when the diffraction pattern is viewed at a long distance from the diffracting object, and also when it is viewed at the focal plane of an imaging lens....

, which states that the intensity

Intensity (physics)

In physics, intensity is a measure of the energy flux, averaged over the period of the wave. The word "intensity" here is not synonymous with "strength", "amplitude", or "level", as it sometimes is in colloquial speech...

 of light scattered by a particle is directly proportional to the size of the particle.

The laser is passed through the substance being examined, and the diffracted light

Light

Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...

focused onto a detector which measures the angular distribution of the intensity of the scattered light.