Non-adiabatic effects in population transfer in three-level systems

We present an analytically solvable model for stimulated Raman adiabatic passage (STIRAP) processes in three-level systems. It involves realistic separated pulses which vanish at infinite times, whose pulse areas are finite and whose envelopes are smooth functions of lime. The solution is obtained using the correspondence between three-level systems on resonance and two-level systems. The analytic model confirms the breakdown of the Dykhne-Davis-Pechukas exponential dependence of the non-adiabatic transition probability on the adiabaticity parameter found numerically recently.