Population transfer between valence states via autoionizing states using two-color ultrafast $\pi$ pulses in XUV and the limitations of adiabatic passage

Population transfer between two valence states of the Li atom with a Raman process via intermediate autoionizing states well above the ionization threshold is investigated using a recently developed implementation of the muticonfiguration time-dependent Hartree Fock method. It is found that a properly chosen sequence of pump and Stokes $\pi$ pulses can yield a population transfer efficiency of $53\%$ at relatively low intensities, while the extension of the stimulated Raman adiabatic passage (STIRAP) approach to the XUV in this case is far less efficient and loses its characteristic robustness at high intensities. A rule of thumb for when STIRAP is practical is given, suggesting that at still shorter wavelengths STIRAP may be possible.

Figure 1

Schematic diagram of the population transfer process with the intermediate state embedded in the ionization continuum.

Figure 2

Population dynamics for (a) the three-level model simulation results and (b) MCTDHF results, with the $\pi +\pi$ pulse configuration.

Figure 3

MCTDHF simulation results: (a) Population transfer efficiency as a function of the Stokes pulse intensities (peak value). Filled circles: $\pi +\pi$ pulse configuration. Filled squares: STIRAP configuration. Chained vertical line denotes the adiabatic limit. (b) Population dynamics for the STIRAP configuration with time delay of $t_S-t_p=3$ fs.