One- and two-photon-dressed effects in infrared-coupled quantum wells

We investigate the conduction intersubband linear response of an n-type quantum well driven by two coherent optical fields with arbitrary strengths. The optical fields couple two excited conduction subbands to a common excited subband with either higher energy (Λ configuration) or intermediate energy (Ξ configuration). The system is then monitored weakly from the uncoupled partially occupied ground conduction subband. We find that the driven Λ system supports two different coupling mechanisms: (i) indirect two-photon coupling of the two lower-energy-excited subbands through the third one (Raman coupling), and (ii) one-photon coupling of all three coupled excited subbands. It is shown 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 Ξ system. The manifestations of these mechanisms are discussed and the detailed evolutions of the coupled systems in both high-and low-field intensity cases are investigated. Also, the infrared coupling of quantum wells with large conduction-band offsets with a single field are studied using the results for the Ξ configuration. The role played by the damping rate of each subband in the infrared coupling of the quantum-well conduction band is discussed. © 1996 The American Physical Society.