POLARIZATION OF A DIPOLE GAS UNDER A RESONANT INTERACTION WITH A STRONG BICHROMATIC FIELD

An interaction of an atomic/molecular medium with two strong electric fields E(L)(t) and E(M)(t) is investigated. The frequency omega(L) of the first (laser) field E(L)(t) is close to a transition frequency ome ga(21) between an upper (2) and a lower (1) atomic levels while the se cond field E(M)(t) is of a much lower frequency omega(M) much less tha n(21). The medium is a dipole gas characterized by a nonzero averaged value of electric dipole moment in the states 1 and/or 2. An analytica l solution of equations for the density matrix of a dipole atom/molecu le interacting with the fields E(L)(t) and E(M)(t) is found using the second approximation of the averaging method by Krylov-Bogoliubov-Mitr opolskii. The solution obtained is valid in a much broader range of fi eld strengths than an analogous solution that could have been found by the usual time-dependent perturbation theory. Using the solution obta ined for the density matrix, polarization of a dipole gas interacting with the fields E(L)(t) and E(M)(t) is analytically calculated. This a nalytical expression for polarization of such media can be utilized fo r study of various nonlinear optical phenomena. One of the phenomena i s a generation of waves at frequencies omega(L) +/- p omega(M) and (p + 1)<omega(M) p = (where p = 1, 2, 3,...) in a dipole gas. Another phe nomenon is an amplification of the incident wave of the lower frequenc y omega(M) due to a stimulated scattering in a dipole gas.