Absorption integrated over all frequencies

To form an estimate of the total spectral strength of the classical oscillating electron, we integrate the absorption over all frequencies thus  

If we assume that the natural frequency mo of the oscillating or dispersion electron occurs at a very high value so that the kernel of the integral is nearly zero at the lower limit, we can drop the lower limit to —oo, in which case the integration can be performed exactly and 

There is also the implication in this procedure that the line must be discrete, i.e. this procedure cannot be applied to a continuum, since an integral over all frequencies would then diverge. The question of how to describe continua is considered in subsection 4.6.1. 

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