Eitan Ehrenfreund

TL;DR: In this article, the authors report on picosecond time resolved spectroscopy of photogenerated infrared active vibrations in thin films of 2,5-dioctyloxy poly(phenylene vinylene).

TL;DR: In this paper, the excitation profile of the absorption spectrum due to photoexcited polarons and bipolarons in the non-degenerate ground state conjugated polymer poly(3-methylthiophene) was analyzed.

TL;DR: A unique feature of charge transfer excimers that are responsible for MPC: sub-ns fast fusion back to singlet excitons and slow (ns to μs) dissociation to free charges is attributed to.

TL;DR: In this paper, a transient interband-pump-intersubband-probe technique was applied to directly measure the time it takes for resonantly photoexcited excitons in GaAs/AlGaAs superlattices to redistribute in momentum space.

Abstract: The thermalization of resonantly excited two-dimensional excitons in $\mathrm{GaAs}/{\mathrm{Al}}_{0.33}{\mathrm{Ga}}_{0.67}\mathrm{As}$ superlattices is studied using time-resolved photoinduced intersubband absorption. Resonantly photogenerated excitons are sharply distributed in momentum space around the wave vector of their parent photons. We measured the time it takes for these excitons to redistribute evenly over the whole superlattice Brillouin zone and found it to be a few tens of picoseconds. This time depends on the initial density of excitons ${N}_{X}$ as ${N}_{X}^{\ensuremath{-}0.7}$ and on the superlattice period ${L}_{z}$ approximately as ${L}_{z}^{\ensuremath{-}8}.$ We discuss an excitonic momentum space self-diffusion model, which describes the strong dependence on the superlattice period. We conjecture that exciton-exciton scattering is the dominant cause for this diffusion.