Generation of s-polarized surface-like electromagnetic waves during nonlinear resonant light scattering

Abstract

Surface electromagnetic waves (SEWs) represent an electromagnetic field that is localized near the interface between two linear media and propagates along this boundary [1]. As is well known, s polarized SEWs (or E waves, in which the electric vector E is perpendicular to the plane of propagation [1]) cannot exist because boundary conditions are not satisfied. The existence of p polarized waves (i.e., those with the E vector lying in the plane of wave propagation) is allowed, provided that the dielectric permittivity ε in one medium is either real and negative (Fano waves) or complex (Zenneck waves). In the former case, the phase velocity is lower than the velocity of light in vac uum (v < c), while the second case corresponds to v > c. The Fano waves are readily observed in experiment and have been widely used in various investigations. The situation with regard to the Zenneck waves is more complicated and, although they have been reported as observed [2, 3], some uncertainty (even in respect of their existence) is still retained [4].Naturally, a question arises concerning the possi bility of exciting s polarized electromagnetic fields similar to SEWs (in particular, Zenneck waves) at the interface between linear and nonlinear media. The possible appearance of inhomogeneous s polarized waves in nonlinear processes was pointed out long ago (see, e.g., monograph [5]). However, these waves did not receive much attention at that time, since they rapidly decayed with increasing distance from the interface [5], and the attention of researchers was devoted mainly to the field of radiation far from the interface.This Letter shows the possibility of exciting a sys tem of two inhomogeneous s polarized waves that propagate at the same phase velocity over both sides of a nonlinear dipole monolayer and resemble SEWs.Consider a transparent dielectric medium with permittivity ε(ω), in which a nonlinear resonant monolayer of randomly but uniformly arranged non interacting dipoles is situated in the xy plane that intersects the z axis (at z = z 1 ) of a Cartesian coordi nate system. Let a classical monochromatic wave E 0 exp(iω 0 t -ik 0 r) with frequency ω 0 and wave vector k 0 be incident onto this monolayer from half space z < z 1 at angle α, so that the vector k 0 occurs in the yz plane and has two nonzero components, k 0 = (0, k 0y , k 0z ). A nonlinearity of the interaction of atoms with a strong coherent incident field leads to rearrangement of the structure of atomic energy levels. As a result, the spectrum of oscillations of the induced atomic dipole moment consists of three components with the fre quencies ω 1 = ω 0 -Δ, ω 2 = ω 0 , and ω 3 = ω 0 + Δ (Mol low triplet [6]), where Δ = is the general ized Rabi frequency, Ω = ω 0 -ω mn is the detuning of the incident field frequency ω 0 from the atomic transi tion frequency ω mn , V 0 = D mn E 0 /ប, and D mn is the matrix element of the dipole moment of the m-n atomic transition between the corresponding combi nation levels. An analogous situation involving a spec tral trip...