Photorefractive effect produced by photoinduced metastable changes in the dielectric constant

Experimental evidence indicating a new mechanism for the photorefractive effect is presented. A new experimental technique enabling the distinction between this mechanism and the space-charge mechanism is described. It is shown that illumination-induced changes in the refractive index of $\mathrm{K}{\mathrm{Ta}}_{1-x}{\mathrm{Nb}}_x{\mathrm{O}}_3$ in the paraelectric phase result from metastable changes in the dielectric constant. A possible microscopic model attributing these changes in the dielectric constant to changes in the phase-transition temperature is discussed. Quantitative comparison between the two mechanisms in $\mathrm{K}{\mathrm{Ta}}_{1-x}{\mathrm{Nb}}_x{\mathrm{O}}_3$ is presented and the application potential of the new mechanism is discussed.