Abstract

We study unidirectional three-wave spectroscopy for which one pump and two probe waves beat in a nonlinear medium at the frequencies ±Δ with respect to the pump. Field transmission spectra change as the fields propagate through the medium due to probe variations in both amplitude and phase. In a homogeneously broadened two-level system, the rates of change in sidemode amplitudes and phases are determined by the effectiveness of the population pulsations in coupling the fields. For cases in which the population difference lifetime T₁ is comparable with the dipole lifetime T₂, the strong coupling between the sidemodes and the pump leads to fast amplitude change, while strong coupling between the two sidemodes leads to fast phase change. When the pump Rabi flopping frequency Ω ≅ Δ and Δ ≅ 1/T₁, the population pulsations couple the two sidemodes most efficiently, causing the sidemode phases relative to the pump phase to vary rapidly. When Ω ≅ 2Δ, the pump field scatters strongly off the population pulsations, thereby amplifying the sidemode fields. When Ω ≫ Δ, the population pulsations become too weak to couple the fields significantly, and phase, amplitude, and spectral features in general change very slowly.

© 1988 Optical Society of America