Semiclassical treatment of multiphoton interactions: ac Stark shifts

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Abstract
The extraction of ac Stark shifts and splittings from a semiclassical treatment of multiple wave-atom interactions is considered. Within the rotating-wave and quasistatic approximations, we show that the information can be extracted from the complex Beer's coefficient sensed by a weak tunable probe wave, whose lower level is fully populated and unconnected to the strong fields. This situation leads to a great simplification of the density-matrix equations of motion, from which algorithms are derived for the algebraic construction of the Beer's coefficients appropriate to other cases not treated. Both level-shifted resonance and line-strength information are contained in the Beer's coefficient, many examples of which are given, some for the first time. Generalized sum rules for the transitions are derived along with a connection of this approach to other approaches including dressing transformations.