Photorefractive effects and photocurrents in KNbO3: Fe

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Abstract
Holographic measurements of optically induced refractive index changes (light damage) of Fe doped KNbO3 are interpreted in terms of photoconductivity results. In “undoped” KNbO3 the light damage is one order of magnitude smaller than in LiNbO3-The light induced index changes can be drastically reduced or enhanced by applying a relatively small de-field along the polar ±c axis. The space-charge field due to the “photovoltaic effect” is then increased or decreased by photoconductivity.The spatial frequency dependence of the light-induced index changes indicates, that diffusion processes of charge carriers are important for the light damage in KNbO3 if the fringe spacing α of the recorded hologram is smaller than 2 μm. For α = 0.35 μm this term is two orders of magnitude larger than the “photovoltaic effect” and the photoconductivity term.The dispersion of the absorption-and photoinduced current-density measurements yield basic information on the energy levels of the photorefractive centers controlling the index damage.