Calculation of Multiphoton Transition in Li Atoms via Chirped Microwave Pulse

The position and width of avoided crossings of Li atom energy levels in a static electric field is presented by using the B-spline basis set method combined with the model potential. Using the time-dependent multilevel approach, the population of Li atoms is transferred to the target state completely by one-photon, two-photon or a single multiphoton adiabatic rapid passage, which requires only a small frequency sweep. The calculation results agree well with the experiment and novel explanations are given to understand the experimental results.