Interaction of non-monochromatic laser field with two-level atom

The problem of a two-level atom interacting with a non-monochromatic radiat ion pulse is studied in the resonant approximation for arbitrary detunings, and without the resonant approximation. By using the time-dependent theory of perturbation the analytical expressions for the transition probability and induced dipole moment of the atom are obtained. It is shown that the up per level population of the atom exhibits oscillations that are absent in t he resonant approximation. The temporal shape of the pulse is shown to affe ct significantly the atomic transition probability. The behaviour of the tr ansition probability and dipole moment spectrum for arbitrary pulse shapes, phases and detunings is investigated. The interference between the spectra l components arising in nonlinear processes is shown to play a considerable role in the formation of a dipole moment spectrum.