Stimulated Raman adiabatic passage with small two-photon detunings and its geometrical description

A simple theoretical approach to stimulated Raman adiabatic passage (STIRAP) with small two-photon detunings is presented. The STIRAP process in a tripod configuration with small two-photon detunings is investigated. It is shown that the processes can be regarded as standard STIRAP processes via dark states even in the presence of the two-photon detunings. A geometrical description for these processes is also presented.