Silicon Photonics: Fundamentals and Devices

9.3 Simplified Theory of Raman Scattering

The theory presented in this section is based on electromagnetic (EM) theory and closely follows the treatment given by Wang 5.

In the classical explanation of Raman scattering, a lightwave with an electric field falling on a molecule induces a dipole moment given by

(9.9)

In the absence of vibration or rotation of molecules, the polarizability α is a scalar; however, molecules do have vibration or rotation, and consequently the induced polarization changes with direction leading to the tensorial nature of α. The phenomenological expression for α may be written as

(9.10)

where denotes the angular frequency of one of the Fourier components of the vibration spectra and is the random phase angle for spontaneous process. Substituting Eq. (9.10) in Eq. (9.9) shows that the induced dipole moment and hence the scattered light have three components: the original wave with angular frequencies and two additional waves with angular frequencies , representing ...