2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/108420We derive simple difference formulas describing a small-signal absorption of THz field in a semiconductor superlattice driven by a microwave pump. We give a transparent geometric interpretation of these formulas that allows a search of optimum conditions for the gain employing only a simple qualitative analysis. Our theoretical approach provides a powerful tool for finding the correspondence between quasistatic and dynamic regimes in ac-driven semiconductor superlattices.Submitted to proceedings of 4th Int. Symp. Nanostructures: Physics and Technology (St Petersburg, Russia, June 26-30, 2006). For detailed consideration see in cond-mat/0602209Mesoscale and Nanoscale Physicstext