Abstract

Extensive studies have been carried out on the large optical nonlinearities associated with excitonic or band gap resonances in semiconductors.¹ Together with these absorptive-resonance nonlinearities is a quasicontinuum or background nonlinearity that is small but not entirely negligible. The characteristic of this background nonlinearity is an ultrafast recovery time owing to its electronic origin. This work is concerned with measurement of this third-order nonlinear susceptibility χ⁽³⁾ in AlGaAs/GaAs heterostructures using picosecond nondegenerate four-wave mixing in the waveguide configuration. The two key aspects of this study are the picosecond-scale time resolution that ensures that only the ultrafast nonlinearity, and not the carrierdependent long-lived effects, is measured and the large four-wave mixing signals that result from the long interaction distance in waveguides.²

© 1990 Optical Society of America