Ultrafast Spectral Interferometry of Resonant Secondary Emission from Quantum Wells: From Rayleigh Scattering to Coherent Emission from Biexcitons

Recent investigations of secondary emission from quantum well excitons following ultrafast resonant excitation have demonstrated an intricate interplay of coherent Rayleigh scattering and incoherent luminescence. We have very recently demonstrated that it is possible to isolate and time resolve the coherent field associated with the Rayleigh component using ultrafast spectral interferometry or Tadpole, thus, obtaining substantial and new information of the nature of resonant secondary emission. Our observation demonstrates that Rayleigh scattering from static disorder is inherently a non-ergodic process invalidating the use of current theories using ensemble averages to describe our observations. Furthermore, we report here a new and hitherto unknown scattering mechanism involving the two-photon coherence associated with the biexciton transition. The process leaves an exciton behind taking up the recoil momentum and is hence intrinsic and instantaneous.