ENERGY-LEVEL SCHEMES FOR FAR-INFRARED QUANTUM-WELL LASERS

We analyze the physics of three-level and Four-level systems for optic ally pumped far-infrared quantum well lasers. The higher complexity of the four-level system offers a great advantage because it gives more flexibility to design the dipole matrix elements and phonon scattering rates to enhance both? the gain and emission efficiency. We propose a four-level scheme that is superior in gain and emission efficiency by an order of magnitude over previous designs. (C) 1998 American Instit ute of Physics.