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 omega(21) between an upper (2) and a lower (1) atomic levels while the second field E(M)(t) is of a much lower frequency omega(M) much less than(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 analytical solution of equations for the density matrix of a dipole atom/molecule interacting with the fields E(L)(t) and E(M)(t) is found using the second approximation of the averaging method by Krylov-Bogoliubov-Mitropolskii. The solution obtained is valid in a much broader range of field strengths than an analogous solution that could have been found by the usual time-dependent perturbation theory. Using the solution obtained for the density matrix, polarization of a dipole gas interacting with the fields E(L)(t) and E(M)(t) is analytically calculated. This analytical expression for polarization of such media can be utilized for study of various nonlinear optical phenomena. One of the phenomena is 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 phenomenon is an amplification of the incident wave of the lower frequency omega(M) due to a stimulated scattering in a dipole gas.