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

Abstract

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 (\ensuremath{\Lambda} configuration) or intermediate energy (\ensuremath{\Xi} configuration). The system is then monitored weakly from the uncoupled partially occupied ground conduction subband. We find that the driven \ensuremath{\Lambda} 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 \ensuremath{\Xi} 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 \ensuremath{\Xi} configuration. The role played by the damping rate of each subband in the infrared coupling of the quantum-well conduction band is discussed. \textcopyright{} 1996 The American Physical Society.