Dipolar Models

Abstract

In this section we propose to describe the effects that are peculiar to the coupled electromagnetic-field-lattice-oscillator system. In this regime, which is of importance only when the finite wavelength of E and H cannot be ignored, the transverse normal modes of the system assume a “mixed” character, being neither purely mechanical oscillations nor pure light waves. These hybrid modes have been given the name “polaritons” and have been observed by Raman scattering,^(37,38) which confirmed the basic ideas developed by Huang.^(26,27) However, to observe these excitations in this way, one has to use a noncentrosymmetric material such as gallium phosphide. The present theory is exact for such zinc-blende structures.