Subbarrier resonances in the inelastic channel during slow atomic collisions in a laser field

M. Ya. Agre, Л. П. Рапопорт

A. D. Gazazyan, E. A. Gazazyan, V. O. Chaltykyan

Collisions of atoms with formation of Feshbach resonances in the presence of laser field are considered. The elastic and inelastic scattering cross sections are calculated. The laser field leads to second resonance in elastic scattering, broadening of resonances, and arising of interference between resonant and potential scattering. The effects associated with interference of the two channels of decay of bound system of two atoms (a molecule) in laser field are studied. It is shown that if the energy equals that of the lower stable Stark-shifted level plus the energy of two photons, the resonance is quenched. It is also shown that with the increase in two-photon effective interaction the pattern of resonance scattering changes essentially.

E. A. Gazazyan, A. D. Gazazyan, V. O. Chaltykyan

Resonance scattering with formation of Feshbach resonance in the presence of laser radiation in the case of the decays in open and closed channels is considered. The presence of the resonant laser radiation leads to additional channels of the elastic and inelastic scattering. The cross sections of the elastic and inelastic scattering are obtained which show that they are determined by two interconnected phases of resonance scattering and interference phenomena are observed.

Robert E. Walkup, Alan L. Migdall, David E. Pritchard

We report observations of inelastic collisions of atoms excited by a weak monochromatic laser field whose frequency is close to the resonance frequency of the transition from the ground state to an excited state. Our experiments use sodium atoms in a gas cell with the laser frequency detuning from resonance ($|\ensuremath{\Delta}|<6$ GHz) much smaller than the inverse of a collision duration. In this frequency region, our results may be interpreted in terms of inelastic collisions involving virtually excited atoms. The inelastic collision rate is determined by measuring the ratio of fluorescence from the collisionally populated level to emission from the laser populated level. By studying this emission ratio as a function of perturber pressure we show that the inelastic collision rate constant for virtually excited atoms is the same as the thermally averaged rate constant for level-to-level population transfer. Measurements of the emission ratio as a function of the laser detuning from resonance explicitly show how the correlation of collision rates with excitation frequency due to the Doppler effect is lost as the laser is tuned more than several Doppler widths from line center. The collisions of virtually excited atoms fundamentally limit experiments utilizing the Doppler effect to obtain velocity-dependent excited-state collision rates.

Борис М. Смирнов