Nonlinear optical response of a dense two-level atom system embedded in a linear dielectric medium

The nonlinear optical (local) response of a dense collection of two-level a toms embedded in a linear dielectric medium is investigated theoretically. The nonlinear response of absorption and dispersion of two-level atoms asso ciated with a weak probe field in the presence of a strong pump field is ca lculated in terms of the linear response theory. The numerical results show that the absorption and dispersion spectra are different from those in vac ua because of the local-field effect enhancement and the local cooperative effect.