title: Microscopic measurement of photon echo formation in groups of individual excitonic transitions.
abstract: The third-order polarization emitted from groups of individual localized excitonic transitions after pulsed optical excitation is measured. We observe the evolution of the nonlinear response from the case of a free polarization decay for a single transition, to that of a photon echo for many transitions. The echo is shown to arise from the mutual rephasing of the emission from individual transitions.
authors.affiliation: Department of Physics and Astronomy, Cardiff University, Cardiff CF24 3YB, United Kingdom. LangbeinWW@cardiff.ac.uk
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Langbein
authors.forename: Brian
authors.initials: B
authors.lastname: Patton