The photorefractive properties of semi-insulating AlGaAs-GaAs multiple quantum wells are described for the transverse Franz-Keldysh geometry with the electric field in the plane of the quantum wells. Combining the strong electroabsorption of quantum-confined excitons with the high resistivity of semi-insulating quantum wells yields large nonlinear optical sensitivities. The photorefractive quantum wells have effective nonlinear optical sensitivities of n2 103 cm 2 /W and a2/ao =: 10 4 cm 2 /W for applied fields of 10 kV/cm. Photorefractive gains approaching 1000 cm-' have been observed in two-wave mixing under dc electric fields and stationary fringes. The transverse Franz-Keldysh geometry retains the general transport properties and behavior of conventional bulk photorefractive materials. The resonant excitation of free electrons and holes in the quantum wells leads to novel behavior associated with electron-hole competition. We demonstrate that under resonant excitation of electrons and holes the device resolution is fundamentally limited by diffusion lengths but is insensitive to long drift lengths.

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Femtosecond pulses can be shaped in the time domain by diffraction from dynamic holograms in a photorefractive multiple quantum well placed inside a Fourier pulse shaper. We present several examples of shaped pulses obtained by controlling the amplitude or the phase of the hologram writing beams, which modifies the complex spectrum of the femtosecond output.

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Intervalley scattering of hot electrons during high-field transport in transverse-field photorefractive quantum wells induces a nonlocal optical response in which photoinduced changes in the refractive index are spatially shifted relative to the optical stimulus, providing an avenue for optical gain. We demonstrate that the onset of the photorefractive phase shift coincides with the onset of velocity saturation. This nonlocal response is the high-resistivity consequence in semi-insulating semiconductors of the Gunn effect mechanism.

The diffraction of 100-fs pulses from the static gratings of photorefractive quantum wells (QW's) produces diffracted pulses that are nearly transform-limited, despite the strong dispersion near the quantum-confined excitonic transitions. This quality makes the QW's candidates for use in femtosecond pulse shaping, although the currently limited bandwidth of the quantum-confined excitonic transitions broadens the diffracted pulses. Femtosecond electric-field cross correlation and spectral interferometry techniques completely characterize the low-intensity pulses diffracted from stand-alone photorefractive QW's, and from QW's placed inside a Fourier-domain femtosecond pulse shaper.

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