Intersubband Third-Order Nonlinearities in a GaAs/AIGaAs Step Quantum Well Structure by Phase Conjugation Method

In this letter, we present the observation of phase conjugation at 9.27μm in a GaAs/AlGaAs multiple step quantum well structure. The response is caused by the nearly resonant intersubband transition. The magnitude of x⁽³⁾ determined by this phase conjugation method is about 8 x 10^-5 esu and the phase conjugate reflectivity η is about 6 x 10^-3 uncorrected for Fresnel reflections.