2 research outputs found
Few-photon single ionization of cold rubidium in the over-the-barrier regime
Photoionization of the rubidium (Rb) atoms cooled in a magneto-optical trap,
characterized by the coexistence of the ground 5 and the excited
5 states, is investigated experimentally and theoretically with the
400 nm femtosecond laser pulses at intensities of W/cm -
W/cm. Recoil-ion momentum distribution (RIMD) of Rb
exhibits rich ring-like structures and their energies correspond to one-photon
ionization of the 5 state, two-photon and three-photon ionizations of
the 5 state, respectively. With the increasing of , we find that
experimental signals near zero-momentum (NZM) in RIMDs resulted from the
5 state enhance dramatically and its peaked Rb momenta dwindle
obviously while that from the 5 state is maintained. Meanwhile, the
ion-yield ratio of the 5 over the 5 states varies from to
as increases. These features indicate a transition from
perturbative ionization to strong-perturbative ionization for the 5
state. Numerical simulations by solving the time-dependent Schr\"odinger
equation (TDSE) can qualitatively explain the measurements of RIMD, photoion
angular distributions, as well as ion-yield ratio. However, some discrepancies
still exist, especially for the NZM dip, which could stem from the
electron-electron correlation that is neglected in the present TDSE simulations
since we have adopted the single-active-electron approximation