Semiclassical dressed states of two-level quantum systems driven by non-resonant and/or strong laser fields

Analytical expressions for the semiclassical dressed states and correspondi ng quasienergies are obtained for a two-level quantum system driven by a no nresonant and/or strong laser field in a coherent state. These expressions are of first order in a proper perturbative expansion, and already contain all the relevant physical information on the dynamical and spectroscopic pr operties displayed by these systems under such particular conditions. The i nfluence of the laser field parameters on transition frequencies, selection rules and line intensities can be easily understood in terms of the quasie nergy-level diagram and the allowed transitions between the different semic lassical dressed states.