Four-Wave Mixing Scheme in a Four-Level Ladder-Type Atomic System Based on Electromagnetically Induced Transparency

A nonlinear optical four-wave mixing scheme is presented and analysed for the generation of coherent light in a nearly four-level ladder-type atomic system in the context of electromagnetically induced transparency (EIT). We find that EIT can suppress nonlinear photon absorption and the peak of the generated mixing field is located at the centre of the transparency window where the loss is minimal, though there is a dip in the centre. Such a nonlinear optical process can also be used for generating coherent short-wavelength radiation.