Stimulated Raman adiabatic passage with amplitude modulated fields

We discuss stimulated Raman adiabatic passage (STIRAP) for pulses whose amplitude is modulated with constant frequency. We discuss in detail the case of a Lambda (Raman) system driven by two amplitude-modulated pulses. We present a variety of numerical solutions to the relevant Schrödinger equation, which we interpret using the Floquet theorem for the solution of systems of linear equations with periodic coefficients, the concept of quasienergies, and the assumption of adiabatic evolution. We find thresholds for successful population transfer and show that some peculiarities of the depicted efficiency of population transfer can be interpreted as pairs of Landau-Zener transitions in the areas of avoided crossings of quasienergies. We provide an analytic expression for the transfer efficiency in these cases. We show that the efficiency of population transfer is much more sensitive to the population decay from the upper level than in the case of smooth (non modulated) laser pulses. We note the applicability of the results to cases beyond the rotating wave approximation.