Short-pulse population inversion and transmittance

The maximal population transfer in a two-level system induced by an ultrashort, linearly polarized laser pulse and the optimal pulse shape for maximal population transfer depend critically on the pulse duration and phase. In the case of temporally symmetric pulses, half-cycle pulses are optimal and are capable of inverting the population completely. For antisymmetric pulses, bimodal pulses are optimal but cannot invert the population completely. Deviations from the Rabi formula for the pulse parameters do not occur until the pulses become shorter than a few optical cycles.