Properties of stimulated Raman adiabatic passage with intermediate-level detuning

We analyse the effect of the intermediate-level detuning on the efficiency of the stimulated Raman adiabatic passage process in three-level systems. We present an exactly solvable analytic model, involving smooth delayed pulses, as well as numerical results and an analytic approximation for Gaussian pulses. Both types of pulses demonstrate that for fixed pulse strengths, the transfer efficiency is adversely affected as the intermediate-level detuning increases because of the deteriorating adiabaticity and eventually vanishes for very large detuning. It is shown that the width of the detuning range, over which the transfer efficiency remains high, is proportional to the squared pulse area. A simple analysis suggests that this feature should be generally valid for any smooth delayed pulses.