Lichtscattering

Lichtscattering, or light scattering, is the deflection and redistribution of light by matter. When light encounters particles or inhomogeneities in a medium, its direction, phase, or wavelength may change due to interactions with the material's electrons, molecules, or lattice. Scattering can be elastic, in which the scattered light retains its wavelength but changes direction, or inelastic, where energy is exchanged and the wavelength shifts (as in Raman or Brillouin scattering). The strength and angular distribution of scattering depend on the wavelength of light relative to the size and refractive index of the scatterers.

Two common regimes are Rayleigh scattering, with particles much smaller than the wavelength, yielding a strong wavelength dependence (shorter wavelengths scatter more strongly) and explaining blue skies and red sunsets; and Mie scattering, for particles comparable to or larger than the wavelength, producing less wavelength-dependent, often white or gray scattering that explains the appearance of clouds and fog. The Tyndall effect is the visible scattering by colloids. Inelastic scattering, such as Raman scattering, reveals vibrational or rotational modes of molecules.

Applications: atmospheric optics, astronomy, and remote sensing rely on modeling scattering to interpret observations. In biomedical optics, scattering limits penetration but also enables imaging modalities such as diffuse optical tomography. Instrumental methods include nephelometry and spectroscopic scattering measurements, and theoretical tools include the radiative transfer equation and phase functions, with the differential scattering cross section describing angular distribution. Attenuation due to scattering is often described by the scattering coefficient in Beer-Lambert-type relations, especially when absorption is present.