Observation of atomic coherence in laser-excited uranium vapor

For the pair of ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ levels at 3868 and 26 558 ${\mathrm{cm}}^{-1\mathrm{}}$0, the upper-state population was measured as a function of the irradiance of a resonant exciting pulse of fixed duration. The observed damped Rabi flopping showed that the two-level system was partially coherently excited. The results were compared with the prediction of an exact solution of the time-dependent Schrödinger equation for two-level systems excited by a detuned rectangular pulse. The Schrödinger equation solution, after averaging over laser irradiance fluctuations, agrees well with the data.