Multiphoton resonances in atomic bragg scattering

Xudong Yang, Cuifang Qiao, Chuanliang Li +1 more

G. A. Delone, Nikolai B. Delone, G. K. Piskova

G. Grynberg, Bernard Cagnac, F. Biraben

Dylan Manna

Atomic Kapitza-Dirac Bragg regime scattering is a multiphoton process in which a neutral atom undergoes a change of momentum through an interaction with a coherent light source. When the Bragg conditions are met, the outgoing atom beams are spatially quantized. Counterpropagating lasers act as pump and probe scattering from far-off-resonant excited intermediate electronic states, leaving the atoms in the electronic ground state with quantized transverse momentum. Each nontrivial scattering event imparts transverse velocity and therefore kinetic energy to the deflected atoms through recoil. In the Bragg regime, the loss of energy in the light fields is equal to the gain of kinetic energy in the atom. Energy nonconserving intermediate states, which are described by nonadiabatic contributions, are not accounted for by first-order off-resonant states. By comparing the solutions of increasing orders of off-resonant intermediate states, it becomes clear that calculating the correct Pendell\"osung frequencies and phases requires including an ever increasing number of off-resonant states in proportion to the square root of the field strength.

Anthony F. Bernhardt, Bruce W. Shore

We extend the previous theoretical treatment of standing-wave deflection of two-level atoms to include nonresonant excitation, nonorthogonal laser and atomic beams, and excitation duration upper bounded only by atomic relaxation times. Numerically solving equations analogous to those of abruptly initiated multilevel atomic excitation, we find bounds on the maximum deflection fixed by balancing acquired kinetic energy against interaction energy. We find that frequency detuning or nonorthogonal orientation of laser and atomic beams can enhance the deflection and, given sufficiently long interaction time, one can observe deflections at larger discrete angles. We comment on the connection between these Bragg scatterings and multiphoton resonances.