Intersubband-transition-induced phase matching

We suggest the use of the refractive-index changes associated with the intersubband transitions in quantum wells for phase matching in nonlinear materials. An improvement in the conversion efficiency of mid-IR second-harmonic generation by almost 2 orders of magnitude over non-phase-matched bulk GaAs is predicted. We also show that the linear phase contributions of intersubband transitions used for resonant enhancement of second-harmonic generation must be considered, as they could limit the conversion efficiency by increasing the phase mismatch on one hand or offset the bulk's dispersion and lead to phase matching on the other. The second-harmonic generation (SHG) efficiencies of nonlinear materials are often limited by their co-herence lengths,1 and schemes for phase matching or quasi-phase matching2 need to be employed for reasonable conversion efficiencies to be achieved. Recently it was demonstrated that the refractive index of bulk material may be selectively altered by the large refractive-index contributions associ-ated with the intersubband transitions (ISBT's) i