Rayleigh line width scattering

Fig. 7. Typical diagram of the spectrum of scattered light as measured by a Fabry Perot interferometer showing the Rayleigh line (center) and the Brillouin doublet. From the frequency shift and the width of the Brillouin bands one can obtain the storage and loss moduli fin- compresacHKil waves exxuring at hypersonic frequencies...

Except for the last term, which is usually difficult to observe, the light-scattering spectrum is a sum of Lorentzian line shapes. The first term represents an unshifted line called the Rayleigh or central line which is a Lorentzian line with half-width at half maximum... 

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