ULTRAFAST PHASE AND AMPLITUDE DYNAMICS OF COHERENT TRANSIENTS IN SEMICONDUCTOR QUANTUM-WELLS

We present investigations of the temporal evolution of phase and ampli tude of coherent emission of GaAs/GaAlAs quantum well structures, exci ted by ultrashort laser pulses. We find that the coherent light emitte d by excitons or by electron-hole pairs exhibits a complex phase behav ior, which depends critically on the intensity and the central frequen cy of the exciting pulses. We observe nonlinear shifts of the instanta neous frequency within one ultrashort pulsed emission. We also discuss the theoretical interpretation the experiments. Although it is clear that non-local Coulomb correlation and non-Markovian dephasing process es are responsible for the observations, quantitative theories are not available presently. Therefore our experiments, point the need for th eoretical refinements of nonlinear optical processes in semiconductors .