Stimulated Raman adiabatic passage via the ionization continuum in helium: Experiment and theory

We experimentally demonstrate coherent population transfer, driven by stimulated Raman adiabatic passage (STIRAP) between two bound quantum states, coupled via a continuum of states. We present extended numerical and experimental investigations on population transfer from the metastable state 2s S-1(0) to the excited state 4s S-1(0) in metastable helium atoms. While techniques based on incoherent excitation do not permit any population transfer via rapidly decaying continuum states, our data indicate a maximum transfer efficiency of 20% in coherent excitation by STIRAP. We study the transfer efficiency with respect to the relevant experimental parameters. (c) 2006 Elsevier B.V. All rights reserved.