Observation of a large third-order nonlinear response of exciton polaritons in GaAs thin film

We investigated the third-order nonlinear response of excitons in GaAs thin films grown by molecular beam exitaxy. Degenerate four-wave mixing (DFWM) measurements were made using picosecond pulses of 3.2 ps auto correlation width at T=5 K. The DFWM signal of a 110-nm-thick GaAs film at exciton resonance energy is 25 times larger than that of a 1-μm-thick GaAs film. This enhancement is explained by the confinement effect of exciton polaritons, which is due to the nonlocal response of the center-of-mass quantized states of excitons in a radiation field.