Far-infrared generation by doubly resonant difference frequency mixing in a coupled quantum well two-dimensional electron gas system

Far-infrared generation (λ=60 μm) by difference-frequency mixing in a coupled quantum well two-dimensional electron system is reported. Extremely large values of the nonlinear susceptibility are found (χω2−ω1(2)−10−6 m/V) by engineering a doubly resonant structure with narrow intersubband transition linewidths (Γ∼1–2 meV). The effect of many body interactions (depolarization shift) on the frequency dependence of the process is observed.