Femtosecond pump-probe experiments have been carried out on an ensemble of single-wall carbon nanotubes deposited on a glass substrate. Measurements of transient changes of transmission and reflection provide an estimate of the real and imaginary parts of the second-order hyperpolarizability of carbon nanotubes. These values are compared with previous measurements and are discussed in the light of a simple model of the optical nonlinearities near the optical band-gap. (C) 2004 American Institute of Physics.

We present an experimental and theoretical study of the existence of acoustic phonon sidebands in the emission line of single self-assembled InAs/GaAs quantum dots. Temperature-dependent photoluminescence measurements reveal a deviation from a Lorentzian profile with the appearance of lateral sidebands. We obtain an excellent agreement with calculations done in the framework of the Huang-Rhys formalism. We conclude that the only relevant parameter for the observation of acoustic phonon sidebands is the linewidth of the central zero-phonon line. At high temperature, the quasi-Lorentzian quantum dot line appears to be fully determined by the acoustic phonon sidebands.

Time-resolved carrier dynamics in single wall carbon nanotubes is investigated by means of two-color pump-probe experiments. The recombination dynamics is monitored by probing the transient photo-bleaching observed on the first interband transition of the semi-conducting tubes. The carrier dynamics takes place on a one picosecond time scale which is one order of magnitude slower than in graphite. Transient photo-induced absorption is observed with exactly the same dynamics for non-resonant probe conditions and is interpreted as a global red shift of the $\pi-$plasmon resonance. We show that the opening of the band gap in semi-conducting carbon nanotubes determines the non-linear response dynamics over the whole visible and near-infrared spectrum.

Photoluminescence up-conversion under cw excitation in semiconductor quantum-dot structures is systematically studied in a sample exhibiting a crossover between two-dimensional and three-dimensional (3D) growth modes. We probe the existence of carrier up-conversion by using ultrathin quantum wells close to the quantum-dot layer. We show that the efficiency of the up-conversion is closely related to the disorder induced by the 3D-growth mode of the quantum dots. (C) 2002 American Institute of Physics.

We report systematic temperature-dependent measurements of photoluminescence excitation spectra in single self-assembled InAs/GaAs quantum dots. We studied the increase with temperature of the excited-state homogeneous linewidth for different quantum dots. We found a correlation between the acoustic phonon broadening efficiency and the background intensity in the photoluminescence excitation spectra. These results demonstrate the interaction of the discrete quantum dot excited states with a quasicontinuum of states and impose severe limitations on the isolated artificial macroatom scheme for a single quantum dot.

We report systematic linewidth measurements on the fundamental transition of single InGaAs quantum dots. We demonstrate the quenching of the acoustic-phonon dephasing for quantum dots spectrally well separated from the band tail of the wetting layer. We achieve a line narrowing with linewidth of the order of few mueV by tailoring the influence of the electrostatic environment through a decrease of the excess energy in the nonresonant excitation process.

We report high-resolution spectroscopy by interferometric correlation measurements on the photoluminescence signal of a single quantum dot. We demonstrate that the insertion of a Michelson interferometer in the detection path gives a compact and flexible setup for linewidth measurements. We have used this technique to study self-assembled InAs/GaAs quantum dots. We observe linewidth variations from one quantum dot to another, and we bring evidence of environment effects on the broadening processes. (C) 2002 American Institute of Physics.