Degenerate four-wave mixing in room-temperature GaAs/GaAlAs multiple quantum well structures

Abstract

We report the first observation of forward degenerate four-wave mixing (DFWM) in room-temperature GaAs/GaAlAs multiple quantum well structures near the exciton resonances. In a sample 1.26 μm thick with sixty-five 96-Å GaAs quantum wells we observe ∼10−4 diffraction efficiency with ∼30 W/cm2 average intensity from a mode-locked laser. We measure nonlinear absorption and DFWM spectra, and also a change in refractive index, per carrier pair/cm3, of neh∼2×10−19 cm3 just below the heavy hole exciton peak. With 20-ns carrier lifetime this corresponds to an effective nonlinear coefficient for cw beams of ‖n2‖≂2×10−4 cm2/W. This is appreciably larger than previous estimates and encouraging for room-temperature all-optical devices.