Ultrafast Phase Relaxation of Excitons via Exciton-Exciton and Exciton-Electron Collisions

Abstract

The ultrafast relaxation of excitons in GaAs, coherently excited by a short optical pulse and subjected to collisions with free carriers and noncoherent excitons which are independently created by a second synchronized light pulse, is studied directly in the time domain by a probing of the excitonic phase coherence. The relaxation rates reveal strong exciton-exciton scattering with a collision efficiency of 1.6 × ${10}^{-4\mathrm{}}$ ${\mathrm{cm}}^3$ ${\mathrm{s}}^{-1\mathrm{}}$ and even 10 times more efficient exciton-free-carrier scattering.