We study the size dependence of the nonlinear response of weakly confined excitons for the size region beyond the long wavelength approximation regime. The observed degenerate-four-wave mixing signal of GaAs thin layers exhibits an anomalous size dependence, where the signal is resonantly enhanced at a particular thickness region. The theoretical analysis elucidates that this enhancement is due to the size-resonant enhancement of the internal field with a spatial structure relevant to the nondipole-type excitonic state. These results establish the formerly proposed new type of size dependence of nonlinear response due to the nonlocality induced double resonance.
For a system of noninteracting Frenkel excitons in a one-dimensional lattice of size N with periodic boundary conditions, the third-order optical susceptibility g"' has been calculated rigorously in a nonlocal form with arbitrary dependence on external-field frequencies. Among the various terms in g' ' (per unit volume), those explicitly proportional to N in the long-wavelength approximation have been shown to cancel out completely for arbitrary N. The remaining terms, including the effect of nonlocality, reduce to the well-known result of a two-level system in the limit of vanishing transfer energy. There remain N-dependent factors in g ", with different functional forms for even and odd N, but they all approach unity in the limit of large N.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.