Multiple exposure plasma gratings in AlGaAs:DX

We have recently reported a new persistent optical nonlinearity based on the capture and release of electrons from DX centers in certain doped compound semiconductors at low temperatures. This new effect allows for writing diffraction gratings by making localized changes to the carrier density (and hence the refractive index, via the plasma effect) using a non-uniform optical exposure. We have measured peak-to-peak refractive index changes of 0.01, or 30 times larger than those found in conventional photorefractive materials. Here we report measurements on saturation and multiple grating exposures which show that this new medium does not suffer from the erasure problem found in photorefractives: writing later gratings during a multiple exposure does not erase earlier gratings as it does in the photorefractive materials