Rayleigh and Mie Scattering
Rayleigh scattering refers primarily to the elastic scattering of light from atomic and molecular particles whose diameter is less than about one-tenth the wavelength of the incident light.
Rayleigh line refers to the unshifted central peak observed in the spectroscopic analysis of scattered light.
Mie scattering refers primarily to the elastic scattering of light from atomic and molecular particles whose diameter is larger than about the wavelength of the incident light.
Thomson scattering is elastic scattering of light from free electrons.
Raman scattering is inelastic scattering of light from objects whereby the scattered photon has a lower (Raman Stokes scattering) or higher (Raman anti-Stokes scattering) energy than the incident photon.
From ancient times, people have gazed up at the sky in daylight and asked the perennial question “Why is the sky blue?” . Other similar and related questions are “Why is the night sky black?,” “Why are sunrises and sunsets red?,” and “Why are the clouds white?” Rayleigh [2, 3, 4, 5] and Mie scattering  lie behind the long-sought answers to all such questions about the colors seen in the sky.
It is also noteworthy that Rayleigh contributed widely to scattering theory in eight different categories; for an overview of these different contributions, see Reference . However, this entry is limited to a description of classical Rayleigh scattering of light from single small objects such as molecules and atoms. Thus, it is ignoring coherence effects that arise in solids, liquids, and gases at atmospheric pressure or even free electrons where it is known as Thomson scattering.
For particle sizes larger than λ, Mie scattering predominates [6, 12] and for particles that are much larger than λ, a third type of atmospheric scattering, known as nonselective scattering, occurs . A description of this last type of scattering, which can be considered as comprising a combination of Mie scattering, absorption, and multiple scattering, is outside the scope of this entry. Nonselective scattering is not wavelength dependent and is the primary cause of haze in the lower atmosphere. Water droplets and large dust particles can cause this type of scattering.
Representative Scattering Media
Here we review Rayleigh and Mie scattering processes at work in different media of interest, including solids, liquids, and gases. Some examples of practical applications of Rayleigh and Mie scattering in these representative media are also provided.
In fluids, conventional Rayleigh scattering is most commonly observed. Although proof of Rayleigh’s law in gases was obtained quite early on [2, 17], at just a few isolated wavelengths, it was not until later that similar information was obtained over a wide wavelength range. In 1973, Stone  reported on measurements of the Rayleigh scattering from CCl4 and C2Cl4 as a function of wavelength between 600 and 1,060 nm by placing the liquid sample in a hollow fused-quartz fiber and measuring the light scattered by the liquid through the fiber wall. Stone determined that the scattering loss rate was 25 dB/km for CCl4 and 68 dB/km for C2Cl4 at 632.8 nm and that the scattering loss rate followed a λ−4 dependence over the entire spectral range.
Mie scattering is also found everywhere in nature: in the lower atmosphere, as noted above, in fluids like milk and latex paint, and even in biological tissue. In the latter case, Mie theory has been applied to determine if scattered light from appropriately treated tissue can be used to diagnose cancerous from healthy cells [25, 26]. Mie scattering is used in particle size determination for particles in non-absorbing media , in the determination of the oil concentration in polluted water , in parasitology , and in the design of metamaterials .
In summary, it is evident that Rayleigh scattering and Mie scattering are ubiquitous, being found in the everyday and colorful optical wonders that surround us.
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