Scattering (physics and optics)
Scattering: how waves or particles are redirected by matter. Overview of types, mechanisms, history, atmospheric examples, applications and distinctions from absorption, reflection and refraction.
Scattering describes processes in which incoming waves or particles are deflected from their original path after interacting with matter. When radiation or particles encounter atoms, molecules, or larger inhomogeneities, portions of the energy are sent into other directions. Scattering is distinct from absorption, where energy is taken up by the material, and from reflection and refraction, which refer to different boundary behaviors of waves.
Image gallery
5 Images
Common types
- Rayleigh scattering — elastic scattering by particles much smaller than the wavelength; explains why the sky is blue.
- Mie scattering — scattering by particles comparable to the wavelength; important for clouds, fog and aerosols.
- Raman scattering — inelastic scattering of light that shifts wavelength by exciting molecular vibrations; used in spectroscopy.
- Compton scattering — inelastic scattering of high-energy photons by electrons; important in X-ray and gamma-ray physics.
- Other categories include elastic vs inelastic, coherent vs incoherent, and specialized forms such as Brillouin or Rutherford scattering.
Mechanistically, scattering arises from electromagnetic or quantum interactions that redistribute momentum and energy. In many contexts the effect is summarized by a scattering cross section, a quantity that measures the probability of scattering as a function of angle and energy. Coherent scattering preserves phase relationships and can produce interference patterns; incoherent scattering randomizes phases.
Atmospheric scattering provides familiar everyday examples. Tiny air molecules preferentially scatter shorter (bluer) wavelengths — the Rayleigh regime — making the daytime sky blue and producing red sunsets when light travels through more atmosphere. Larger particles such as water droplets produce broad-angle, less wavelength-dependent Mie scattering, so clouds appear white or gray.
Scattering has wide practical importance: remote sensing and lidar use scattered light to profile atmospheres and surfaces; Raman scattering enables chemical fingerprinting; scattering experiments in particle physics reveal internal structure of atoms and nuclei; and in optics, Rayleigh scattering limits transmission in fiber and contributes to optical loss. Medical imaging and ultrasound also rely on understanding acoustic or optical scattering in tissue.
Historically, observations of scattered light (the Tyndall effect) led to theoretical explanations by Lord Rayleigh and others. Later, targeted scattering experiments such as Rutherford's work with alpha particles and Compton's X‑ray studies became cornerstones of modern physics. Distinguishing scattering from absorption, reflection and refraction helps clarify how energy is redistributed when waves meet matter and guides practical applications across science and engineering.
Scattering angle, forward scattering and backward scattering
The scattering angle θ 
is the angle by which the scattered particle is deflected. Forward scattering refers to scattering processes in which only a small deflection occurs (small scattering angle). Backscattering or backward scattering refers to scattering processes with a scattering angle between 
and 
(see also Kinematics (particle impact)).
If both collision partners have a mass different from zero, the scattering angle in the center-of-mass system is often considered in scattering experiments in nuclear and particle physics. This is more important for the theoretical consideration than the scattering angle in the laboratory system.
In many cases, forward scattering is much stronger than scattering in other directions, i.e. it has a comparatively large differential cross-section. A well-known example from everyday life is the scattering of light by dust particles in the air: If you look almost in the direction of the light source (for example, when sunlight falls into a dark room), the dust particles are clearly visible as bright points. Something similar happens to fine water droplets.
Scattering in the backward direction (
) is usually weaker than in all other directions within the framework of classical physics, but can be stronger than scattering in adjacent directions due to quantum mechanical effects or interference effects. Coherent backscattering is also responsible for the high brightness of the full moon.
Classical scattering
Classicalmechanics distinguishes collisions between rigid bodies from scattering at a potential. For orbital motion of a point mass in a potential that decreases linearly with distance, equations always result that describe a conic section: Hyperbola, Parabola, or Ellipse. A positive, i.e. repulsive potential always leads to hyperbolas. Attracting potentials lead to ellipses if the energy of the collision partner is not large enough. In this sense, the movement of a comet is also the scattering at the gravitational potential of the sun.
Related articles
Author
AlegsaOnline.com Scattering (physics and optics) Leandro Alegsa
URL: https://en.alegsaonline.com/art/87813