Nonlinear Optical Processes Using Electromagnetically Induced Transparency

It is well known by those practicing the techniques of nonlinear optics, that the power which may be generated in a frequency summing process, or the gain which may be obtained in a parametric process are determined by the interplay of the nonlinear and linear susceptibilities. In general, as an atomic transition to the ground state is approached, the nonlinear susceptibility is resonantly enhanced, but at the same time the media exhibits a rapidly increasing refractive index and becomes opaque.