Spatial-harmonic gratings at high modulation depths in photorefractive quantum wells

High-order spatial harmonics of photorefractive gratings are detected directly in multi wave mixing experiments in photorefractive AlGaAs/GaAs quantum wells operating in the Franz-Keldysh geometry. We have observed diffraction signals from the first-, second-, and third-harmonic refractive-index gratings. The quadratic electro-optic effect in the quantum wells second-spatial-harmonic grating.