ABSTRACT
The field acting on the atoms in a medium is different from the averaged macroscopic field. The problem of the effective local field caused by dipole–dipole interaction has been discussed several times since Lorentz. In describing the nonlinear optical properties of optically thin resonant layers, it is of principal importance to take into consideration the dipole–dipole interaction of the atoms. These effects manifest themselves when certain relations between the parameters of the atomic system and the incident field are fulfilled. The presence of the excitonic lines shows that the dipole–dipole interaction is larger than the homogeneous and inhomogeneous broadenings. This gives reason to hope that the required inequalities are satisfied in such systems. The chapter considers boundary value problem and a linearly polarized plane wave, with amplitude slowly varying during one optical period, falls perpendicularly onto the surface of a plane-parallel, optically thin, resonant layer consisting of two-level atoms.
