Dynamics of coherent excitation of atoms and molecules: basic problems and applications

This work presents recent results of the investigation and application of the technique of coherent population transfer by counter-intuitive interaction of two radiation fields with atoms and molecules (STIRAP), development and demonstration of the new technique of Stark chirped rapid adiabatic passage (SCRAP) and observation of EIT under conditions of two-photon excitation obtained in collaboration of University of Kaiserslautern (Germany), Universite de Bourgogne (France), Sofia University (Bulgaria) and Institute of Physics of NASU, Kiev (Ukraine). In particular, a novel scheme for complete transfer of atomic or molecular population between two bound states, by means of SCRAP method is suggested, analyzed and demonstrated. In this two-laser technique a delayed-pulse laser-induced Stark shift sweeps the transition frequency between two coupled states twice through resonance with the frequency of the population-transferring coupling laser. The delay of the Stark-shifting pulse with respect to the pulse of the coupling-laser Rabi frequency guarantees adiabatic passage of population at one of the two resonances while the evolution is diabatic at the other. The SCRAP method can give a population-transfer efficiency approaching unity. The success of the SCRAP method with experiments in metastable helium, where a two-photon transition provides the Rabi frequency is demonstrated.