Rayleigh scattering and Mie

Of the scattering processes, only Raman scattering provides easily accessible molecular-specific information, which is important when investigating chemical reactions thus, only this process will be discussed further in this chapter. Nevertheless, both Mie and Rayleigh scattering serve their purpose, and analytical instmmentation based on these processes is marketed commercially (e.g. particle image veloci-metry or particle sizing). 

Bivolaru, D., M. V. Otugen, A. Tzes, and G. Papadopoulos (1999). Image processing for interferometric Mie and Rayleigh scattering velocity measurements, AlAA J., 37(6), 688-694. 

J. I. Gersten, The effect of surface roughness on surface-enhanced Raman scattering, J. Chem, Phys. 72(10), 5779-5780 (1980) Rayleigh, Mie and Raman scattering by molecules adsorbed on rough surfaces, J. Chem. Phys. 72(10), 5780-5781 (1980). 

Besides absorption losses the laser light suffers Mie scattering by aerosols and Rayleigh scattering by molecules in the atmosphere. The total attenuation dl of a monochromatic laser beam at frequency w with intensity 1(0) = Iq is then dl = Iq - I(L) where... 

Spectroscopic examination of light scattered from a monochromatic probe beam reveals the expected Rayleigh, Mie, and/or Tyndall elastic scattering at unchanged frequency, and other weak frequencies arising from the Raman effect. Both types of scattering have appHcations to analysis. 

In contrast to the method based on Rayleigh scattering, the procedure based on Mie scattering theory (a) is not restricted to small particles, (b) chemical absorption may be considered, (c) and lastly, it can be extended to permit the use of a nonlinear... 

For particles below 200 nm, Rayleigh s theory holds, which considers the scattering intensity to be proportional to the 6th potency of the particle diameter. Both Fraunhofer s and Rayleigh s theories are only approximations of Mie s theory which claims that the scattering intensity depends on the scattering angle, the absorption, the size of the particles as well as on the refractive indices of both the particles and the dispersion medium. 

Unlike Rayleigh scattering, which occurs equally in the forward and backward directions, Mie scattering is predominantly in the forward direction, except for the smallest particles. This can be seen in Fig. 9.19, which shows the Mie intensity parameters /, and /, as a function of the scattering angle 6 for three different values of the size parameter a defined by Eq. (Y), assuming the droplets are composed entirely of liquid water (i.e., m 1.333), For a 2.0 and 10 (i.e., D A... 

It is noteworthy that in Fig. 9.20 the function becomes smooth and approaches a variation with D<] as the size parameter decreases toward small values. This is expected, since in the limit of very small particles or molecules, Mie theory reduces to Rayleigh scattering, which, as seen in Chapter 3, varies with D ... 

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