Time-resolved speckle analysis: A new approach to coherence and dephasing of optical excitations in solids

A new method to measure the time-dependent coherence of both homogeneously and inhomogeneously broadened optical excitations in solids is presented. T he coherence degree of resonantly excited light emission is deduced from th e intensity fluctuations over the emission directions (speckles). This meth od determines the decays of intensity and coherence separately, thus distin guishing lifetime from pure dephasing. The secondary emission of excitons i n semiconductor quantum wells is investigated. Here the combination of stat ic disorder and inelastic scattering leads to a partially coherent emission . The temperature dependence is well explained by phonon scattering.