No abstract

An ansatz is proposed for the analytic solution of the Heisenberg equations of a two-level atom in a classical, linearly polarized and intense low-frequency field. According to this ansatz, the motion of the vector representing the state of the atom on the Bloch sphere consists of a fast precession around a direction, which in turn basculates slowly around an axis perpendicular to the field. The time evolution of the atomic state, which is obtained analytically by this vectorial model, is shown to compare quite satisfactorily with the exact numerical solution of the Heisenberg equations. The limits of validity of the ansatz are discussed. The spectrum of the light scattered by the two-level atom is evaluated analytically using the ansatz and it is shown to reproduce very precisely the exact spectrum evaluated numerically. It is shown that the slow component of the motion of the atomic Bloch vector yields the high-order harmonic part of the spectrum, whereas the fast precession gives rise to the hyper-Raman part. The appearance of the overall spectrum is discussed as a function of the various physical parameters of the model. The insight provided by the vectorial model is exploited to investigate the manifest universality of the main features of the overall spectrum and to suggest experiments to test the validity of the vectorial model.

No abstract

No abstract