Efficient two-process frequency conversion through a dark intermediate state

Two simultaneous three wave mixing processes are analyzed, where an input frequency is converted to an output frequency via an intermediate stage. By employing simultaneous phase-matching and an adiabatic modulation of the nonlinear coupling strengths, the intermediate frequency is kept dark throughout the interaction while obtaining high conversion efficiency. This feat is accomplished in a manner analogous to population transfer in atomic stimulated Raman adiabatic passage. Applications include conversion between remote frequencies, e.g., mid-IR to visible, and study of electronic crystal properties in the UV absorption band.