Electromagnetically-enhanced saturable absorption

Electromagnetically-induced transparency (EIT) exploits quantum coherence to burn subnatural linewidth holes within a spectral line. It is typically discussed in the context of a pump-prob e configuration in a three-level Λ system, where the pump is often significantly stronger than the probe. Here we remove such restrictions on the relative intensities of pump and probe fields, and furthermore show that the absorpti ve properties associated with EIT can be of benefit in absorptive nonlinear processes, especially saturable absorption. We show that in a three-level medium near the EIT condition, we can generate saturable absorption qualitatively similar to two-state saturable absorption. The difference is that we can explore saturable absorption against the ground-state dep hasing, rather than spontaneous emission. This has the advantages of significantly more controllability, and more importantly, different intensi ty scalings in the absorption. Such effects could prove useful for signal regeneration at very low light levels, and we provide descriptions of the effect o n semiclassical light fields.