Pump-probe Experiments in Single-quantum-wells

Hoang Ngoc Cam

Zhiping Wang

Tianshu Lai, Luning Liu, Qian Shou +2 more

An elliptically polarized pump-probe spectroscopy is developed. A theoretical model is derived from the rate equations of two-level system with small signal approximation to describe the experimental signal of the spectroscopy. The spectroscopy eliminates the systematic errors between theories and experimental results in present circularly polarized pump-probe spectroscopy, and is implemented easily in experiments. The initial degree of spin polarization of carriers in an excited state can be extracted by means of the spectroscopy, which is an important parameter in the investigation of spatial transport of spin polarization. The electron-spin relaxation in GaAs quantum wells is studied by using this spectroscopy.

Emil S. Köteles, Y. J. Chen, Boris S. Elman

D. Weber, Jochen Feldmann, Ernst Otto Göbel +5 more

We have investigated the coherent dynamics of excitons in a single, a double, and a quintuple quantum-well structure under resonant excitation. In pump-and-probe experiments on the quintuple quantum well we observe a fast decay of the excitonic population within the initial coherent regime. This fast initial population decay is less pronounced for the double quantum well and is almost absent for the single quantum well. The energy linked to the initially lost coherent population is found in the coherent electromagnetic emission induced by the first-order polarization. More specifically, the intensity of this directional light emission increases quadratically with the number of quantum wells. Interference effects and electromagnetic coupling effects between polarizations located in distinct quantum wells probably play a crucial role in the superlinear coherent emission process.

Hanond Nong, Maud Gicquel‐Guézo, Laurent Bramerie +10 more

Ultrafast relaxation dynamics of photogenerated carriers in nanostructure based saturable absorber (SA) are investigated using a degenerate cross-polarized pump–probe experiment at 1.55 µm operating wavelength. Single-walled carbon nanotubes (SWNT) encased in micelles are studied and compared to bundled ones as well as to iron doped InGaAs/InP multiple quantum wells (MQW). SA parameters for all optical signal regeneration (AOSR) are extracted from the normalized differential transmission. Although all samples show the same order of recombination time, SWNT in micelles present a much higher contrast ratio associated to a lower level of saturation fluence as compared to their bundled and MQW counterparts.