Diffraction from optically written persistent plasma gratings in doped compound semiconductors

We propose and demonstrate a new type of optical nonlinearity based on the properties of the DX center in doped compound semiconductors. We report measurements on samples of AlGaAs:Si which were exposed to interfering laser beams and find diffraction from a large, persistent refractive index change associated with the well-known persistent photoconductivity effect in this material. The new effect is shown to exhibit a refractive index change 30 times larger than that of conventional photorefractive materials. We explain the origin of the refractive index change in terms of the plasma effect and show that its expected magnitude is consistent with our observations.