Non-spherical ones can also refract light and may produce a scattering pattern that is superimposed on the diffraction pattern as a spherical particle may. The impact of the refraction is also affected strongly by the shape of the particle. In a measuring system where the spherical particle is constantly changing orientation with respect to the incident light, the pattern is always identical and can give rise to well-defined, reinforced extraneous information that can distort or interfere with the computation of particle size from the diffraction pattern. Refraction can have considerable impact on a diffraction / Mie scattering pattern, but the magnitude of the effect is highly dependent upon the size and shape of the material.Ī sphere will transmit the same refraction pattern regardless of its orientation. The effect on refraction would be to limit the amount of light entering the particle and thus reduce the effect of refraction on a diffraction pattern. Reflection has no effect on diffraction but may affect refraction if the surface is sufficiently reflective. This effect will be discussed below.Īs mentioned above, diffraction / Mie scattering is solely dependent upon the size of the particle. In the case of a diamond, it is refracted and produces the well-known glitter however, when passing through a particle it may add to the Mie Scattering / diffraction pattern. In this case light pass through the particle much as it would through a diamond. Light can also be reflected from the surface of a substance and the use of such data for size measurements would be the subject of a different issue.Ī third occurrence of interaction is a special case that occurs when the material is somewhat transparent. Under these conditions the calculations can be those described by Fraunhofer theory. In these cases, the substance can be assumed to have an extremely high refractive index as well as a large imaginary component (see Transparent particles below). Some materials do not transmit light and absorb the energy. From this Mie scattering pattern information related to the size distribution of the material can be obtained. Mie scattering, at some distance from the particle in the direction of the incident light, is a pattern that will develop depending on the size of the particle and the wavelength of the incident light.
Mie scattering as well as the according Mie theory are named after German physicist Gustav Mie (1868-1957), who calculated the phenomenon for the first time at the beginning of the 20th century. Because the surface of a particle produces an electromagnetic field due to the presence of electrons and since light represents an electromagnetic radiation, it can interact to produce a phenomenon that is described as mie scattering or diffraction.
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