Ultrafast Phase Dynamics Research Articles

The study of ultrafast phase dynamics of carriers in Ge quantum dots by photocurrentcorrelation phase spectroscopy

The ultrafast phase dynamics of carriers in Ge quantum dots (QDs) is studied by usingphotocurrent correlation phase spectroscopy (PCPS) at room temperature. For betterunderstanding the ultrafast phase dynamics of carriers on the sublevels of GeQDs, the sublevels in Ge QDs are first investigated by Fourier transform infraredphotocurrent spectroscopy, and the result shows that there are two sublevels(0.76 and 0.84 eV) in Ge QDs. The ultrafast phase dynamics signals measured byPCPS are well behaved with a smooth wave line and oscillating trailing edge. Thedephasing time has been obtained by numerically simulating the PCPS data interms of optical Bloch equations. The dephasing time () originating in the transition from the sublevel of the Ge QDs to the conduction band isslightly longer than that () originating in the Si band-to-band transition.

Ultrafast phase dynamics of coherent carriers in GaAs

Ultrafast phase dynamics of free-induction decay for carriers in bulk GaAs is studied with differential-phase spectroscopy. The instantaneous phase shifts of the free-induction decay with respect to the excitation pulses are extracted from simultaneously recorded laser pulse autocorrelation and free-induction decay in GaAs. Ultrafast phase dynamics during and immediately after the femtosecond pulse excitation are numerically evaluated with optical Bloch equations using pump pulse and semiconductor exciton parameters as input. Good agreement of the theory with experiment is obtained.

Ultrafast phase dynamics of coherent emission from excitons in GaAs quantum wells.

We investigate the temporal evolution of the instantaneous frequency of ultrashort-pulse four-wave mixing in GaAs/Ga[sub [ital x]]Al[sub 1[minus][ital x]]As quantum-well structures. We find that the coherent light emitted by excitons exhibits a complex phase behavior which depends critically on the density of excitons and the central frequency of the exciting pulses. Depending on the excitation conditions, we observe nonlinear shifts of the instantaneous frequency within one ultrashort pulsed emission or quantum beats. In the latter case we determine that the beat [pi]-phase shift is very fast, only 40% above the fundamental quantum limit. We also present elaborate numerical simulations of the experiments based on a six-band generalization of the semiconductor Bloch equations. This formalism takes into account Coulomb many-body interactions and Pauli exclusion. It reproduces the salient features of the experimental data. It fails to account for important details revealed by the very sensitive phase measurements. The discrepancies can be traced back to two approximations in the theory: the statical treatment of screening, and the Lorentzian description of dephasing. In both cases, this indicates the need for theoretical refinements requiring a microscopic description of Coulomb scattering and dephasing processes in a non-Markovian theory.