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Extinction CoefficientThe parameter used to describe the interaction of electromagnetic radiation with matter is the complex index of refraction, , which is a combination of a real part and an imaginary part. -
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Here, n is also called 'index of refraction' which sometime leads to confusion, and k is called the 'extinction coefficient'. In a dielectric material such as glass, none of the light is absorbed and therefore k = 0. Before a more detail definition of the extinction coefficient k is considered, let us first look at the absorption coefficient α. In a medium absorbing light, the decrease in intensiry per unit lenght is proportional to the value of . In mathematical form this means: -
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- where α is the absorption coefficient.
This can be integrated as: -
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- where is the value of the intensity at the surface of the absorbing medium.
The extinction coefficient k is then defined as -
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- where λ is the vacuum wavelength
Extinction coefficient Extinction coefficient
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