Observation of atomic coherence in laser-excited uranium vapor

For the pair of ²³⁸U levels at 3868 and 26 558 cm^-10, 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 Schr\"odinger equation for two-level systems excited by a detuned rectangular pulse. The Schr\"odinger equation solution, after averaging over laser irradiance fluctuations, agrees well with the data.