Surface polaritons in symmetric nonuniform structures with losses

The conditions for a short-range polariton to exist in a symmetric three-layer model of a planar structure in which the dielectric permittivity goes to zero at a single plane according to a square law are investigated. In the presence of losses, it is shown that surface electromagnetic waves, damped in the direction of propagation and localized in that of variation of the dielectric permittivity, exist for almost all complex values of the latter.