Light Rayleigh

Development of laser sources was followed by the use of special monochromators that can resolve the more-intense, elastically scattered light (Rayleigh line) from the weak, inelastically scattered, Raman signal. The requirement of frequency matching in the double or triple monochromators presents a challenging, coupling problem for frequency-scanning systems. 

Figure 1.2. Raman spectrum of room-temperature chloroform obtained with 514.5 nm light. Rayleigh scattering at zero Raman shift is heavily attenuated by a band reject filter and is actually several orders of magnitude more intense than the Raman scattering. The x axis is shown in three different scales but is normally plotted as Raman shift in reciprocal centimeters relative to the laser frequency (19,435 cm in this case). Although the Stokes Raman to the right is actually a negative frequency shift, convention assigns Stokes Raman shifts as positive numbers.

The first term in equation (7) corresponds to the elastic component of the scattered light (Rayleigh scattering), while the second term corresponds to the inelastically scattered Raman component. Equation (7) also indicates that Raman scattered light can occur at two new frequencies different from the incident light frequency. These correspond to Stokes and anti-... 

When the particle diameter is less than 10% of the wavelength of light, Rayleigh scattering is observed, in which the efficiency factor is given by... 

Incident light Rayleigh scattering Raman scattering... 

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