2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/98715We propose a quantum-dot version of the quantum-well cascade laser of Faist et al. [Science {\bf 264}, 553 (1994)]. The elimination of single phonon decays by the three-dimensional confinement implies a several order-of-magnitude reduction in the threshold current. The requirements on dot size (10-20nm) and on dot density and uniformity [one coupled pair of dots per (180nm)^3 with 5% nonuniformity] are close to current technology.8 pages, REVTEX 3.0, 3 compressed postscript figuresCondensed Mattertext