  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 (STIRAP). Applications include conversion
between remote frequencies, e.g. mid-IR to visible, and study of electronic
crystal properties in the UV absorption band.
