Polarization dynamics and optical selection rules for excitonic transitions in strained quantum wells - art. no. 035302

Dual-beam spectral interferometric techniques are used to time resolve the polarization state of the coherent emission from both intentionally and uni ntentionally strained GaAs/AlxGa1-xAs multiple quantum wells following irra diation with very weak femtosecond pulses. Any anisotropy in the in-plane s train is shown to result in dramatic oscillations in the intensity, the ori entation, and the ellipticity of the coherent emission at the heavy-hole, l ight-hole beat frequency. This behavior is shown to be the result of replac ing the circularly polarized optical selection rules with elliptically pola rized selection rules in the uniaxially strained sample. When only the heav y-hole transition is excited with linearly polarized light, these elliptica l selection rules lead to a linearly polarized coherent emission that is ro tated with respect to the incident orientation. The degree of rotation of t he coherent emission as a function of sample orientation is used to quantif y the anisotropy in the strain. When the in-plane strain is uniform, no suc h rotation and no light-hole, heavy-hole beats in the polarization state of the coherent emission are observed.