Abstract

We report the observation of strong distortions in the temporal profiles of low intensity, transform limited femtosecond pulses (100-150 fs) after traversal through relatively thin GaAs multiple quantum well (MQW) samples. Dramatic pulse distortions were observed, especially close to the exciton resonances at low temperatures, as shown in Fig. 1 for a typical sample with the total thickness of GaAs layers (ℓ) of 6300 Å, excited at the heavy-hole excitonic resonance at 10 K. Thinner samples show less distortion, and the degree of distortion grows very rapidly with ℓ. The pulse shape is a strong function of the dephasing time T₂, as can be seen from Fig. 1: reducing T₂, by increasing the temperature or having a strong pump pulse at an earlier time, has the same effect of reducing the distortion. We show that these pulse distortions, and the change in the distortions caused by a pump-induced change in T₂, have a significant impact on the interpretation of many linear and nonlinear femtosecond experiments.

© 1993 Optical Society of America