The quantum nonperturbative analysis of Kroll and Watson for a two-level system of near-adiabatic atom-atom scattering in an intense laser-field mode is extended to treat a general multilevel system interacting with intense single- or many-field modes. A procedure for rigorously solving the adiabatic eigenvalue problem for the whole charge-field system is given. A new transition-probability formula is derived. Cross sections are calculated for the processes $\mathrm{Li}+\mathrm{H}\left(X{}_{}{}^1{}_{}{}^{}\Sigma _{}^{+}{}_{}{}^{}\right)+\nu \hslash \omega \to \mathrm{Li}+\mathrm{H}(A{}_{}{}^1{}_{}{}^{}\Sigma _{}^{+}{}_{}{}^{} or B{}_{}{}^1{}_{}{}^{}\Pi )$ where $\nu \ge 1$. Analysis of transition in an atom due to intensity variation of a laser pulse shows that desired transition probability per pulse (e.g., ½) may be achieved by varying the pulse parameters. For this, numerical results of $\mathrm{Na}\mathrm{}\left(3s\right)+2\mathrm{}\hslash \omega \to \mathrm{Na}\mathrm{}\left(5s\right)\mathrm{}$ and of $\mathrm{Li}\mathrm{}\left(2s\right)+8\mathrm{}\hslash \omega \to \mathrm{Li}\mathrm{}\left(3s\right)\mathrm{}$ are given.

• Received 4 August 1975

DOI:https://doi.org/10.1103/PhysRevA.13.139