ONE-PHOTON-DRESSED AND 2-PHOTON-DRESSED EFFECTS IN INFRARED-COUPLED QUANTUM-WELLS

We investigate the conduction intersubband linear response of an n-typ e quantum well driven by two coherent optical fields with arbitrary st rengths. The optical fields couple two excited conduction subbands to a common excited subband with either higher energy (Lambda configurati on) or intermediate energy (Xi configuration). The system is then moni tored weakly from the uncoupled partially occupied ground conduction s ubband. We End that the driven Lambda system supports two different co upling mechanisms: (i) indirect two-photon coupling of the two lower-e nergy-excited subbands through the third one (Raman coupling), and (ii ) one-photon coupling of all three coupled excited subbands. It is sho wn that in contrast to the one-photon process, the two-photon process is immune to the higher-energy-excited subband damping rate. The same mechanisms are found for corresponding states of the Xi system. The ma nifestations of these mechanisms are discussed and the detailed evolut ions of the coupled systems in both high-and low-field intensity cases are investigated Also, the infrared coupling of quantum wells with la rge conduction-band offsets with a single field are studied using the results for the Xi configuration. The role played by the damping rate of each subband in the infrared coupling of the quantum-well conductio n band is discussed.