A new method to measure the time-dependent coherence of optical excitations in solids is presented, in which the coherence degree of light emission is deduced from its intensity fluctuations over the emission directions (speckles). With this method the decays of intensity and coherence are determined separately, thus distinguishing lifetime from pure dephasing. In particular, the secondary emission of excitons in semiconductor quantum wells is investigated. Here, the combination of static disorder and inelastic scattering leads to a partially coherent emission. The temperature dependence is well explained by phonon scattering. Spin-relaxation is found to be dominated by disorder, and is preserving the coherence, while phonon-assisted energy-relaxation is foundto destroy the coherence.
|Title of host publication||Festkörperprobleme/Advances in Solid State Physics, vol. 39|
|Place of Publication||Braunschweig|
|Publication status||Published - 1999|