Scattering by Large, Absorbing Particles

All the applications of light scattering that have been discussed so far have been restricted to very small particles and fairly small indices of refraction or to fairly small particles and very small indices of refraction. We have finally reached the point at which it seems appropriate to relax all these restrictions and consider the scattering by a particle of arbitrary size and index of refraction. 

The general problem here is to solve Maxwell s electromagnetic equations both inside and outside a particle, for which the indices of refraction are different in the two regions. The problem has been solved for both spherical and cylindrical particles we limit our considerations to the former. 

On the other hand, suppose the layer consists of a material of refractive index n. The light will now take an increment of time At longer to pass through the layer owing to the delaying effect of the medium. In this case the emerging field would be given by 

The delay may be related to the thickness of the layer and the refractive index as follows  

A very important relationship involving complex numbers is 

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A brief treatment of scattering by large, absorbing particles and the concept of absorption and scattering cross sections are presented in Section 5.7 along with two examples of applications of the Mie theory (to absorbing, but small, particles) and a discussion of Tyndall spectra. 

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