Generation of a difference harmonic in a biased superlattice

We calculate the difference-harmonic susceptibility of a superlattice subject to uniform electric field, where generation of the difference harmonic is caused by interband transitions between hole and electron states. Both the electron and hole states are considered in the framework of the Kane model with parabolic dispersion laws. The hole states are uncoupled while for the electron states we use the tight-binding approximation. We obtain numerical results for spectral dependencies of the susceptibility under the double-resonant generation conditions, and discuss the efficiency of the double-frequency transformation of near-IR pump signal into THz radiation and modifications of the obtained nonlinear response with variation of the electric-field magnitude.