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Probe beam intensities more than an order of magnitude larger than pump beam intensities do not erase photorefractive gratings during nondegenerate four-wave mixing in photorefractive GaAs/AlGaAs quantum wells. The pump and probe laser wavelengths are absorbed in spatially separated regions of the multilayer structure. The photoconductivity of a probe beam around 840 nm is confined to the GaAs quantum wells and cannot easily erase the trapped space-charge gratings in the AlGaAs barriers written by an above-band-gap HeNe laser at 633 nm. This allows a weak visible control beam to modulate a strong infrared signal beam.
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Nolte et al. (1991) studied this question.
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