ABSORPTION SATURATION STUDIES OF LANDAU-LEVELS IN QUASI-2-DIMENSIONALSYSTEMS

We report the first far-infrared linear and non-linear (saturation) ma gneto absorption experiments of coupled subband-Landau level excitatio ns in a series of modulation-doped double-coupled multiple quantum-wel l (MQW) structures. Non-linear spectroscopy is carried out with a free electron laser. A plot of energy versus magnetic field for 4 laser li nes at low intensity and high intensity is compared with linear (Fouri er transform) spectroscopy at low and high temperatures. An exact nume rical solution of the Schrodinger equation for this coupled system is also obtained and compared with experiments. Results show that the fea ture observed at high laser intensity and high temperature is due to t ransitions from the Ist-excited state of the coupled system to the hig her excited states. Based on this, a simple 2-level model is developed , and with a layer-by-layer analysis for MQW systems, the electron lif etime of the first-excited state is obtained. (C) 1997 Academic Press Limited.