lightscattering

Light scattering is the deflection or redirection of light by particles, molecules, or inhomogeneities within a medium. The phenomenon can be elastic, in which scattered photons retain nearly the same energy as the incident photons, or inelastic, where energy is transferred between light and matter (as in Raman or Brillouin scattering). Scattering strength depends on wavelength, particle size and shape, and the refractive index contrast between the scatterer and its surroundings.

Two principal scattering regimes describe spherical particles. Rayleigh scattering applies when particles are much smaller than the wavelength of light; in this limit, scattered intensity increases steeply as particle size decreases and scales roughly with 1/λ4. Mie scattering covers particles comparable to or larger than the wavelength and yields a complex angular pattern that depends on size and refractive index. For free electrons, Thomson scattering is the relevant elastic process. The angular distribution of scattered light is described by a phase function, and the total scattered power is characterized by a scattering cross-section.

The effect is observable in everyday phenomena such as the Tyndall effect, where colloids scatter light, and in atmospheric optics, where Rayleigh scattering gives the blue sky and red sunsets. Scattering by aerosols, clouds, and dust also influences climate models and astronomical observations.

In practice, light-scattering techniques include static light scattering (SLS) for size distributions and molecular weight, dynamic light scattering (DLS) for Brownian-motion-based sizing, and nephelometry for turbidity. Applications span physics, chemistry, materials science, and biomedicine, including optical imaging and tissue spectroscopy.