ENHANCEMENT OF THE AMPLITUDE AND LIFETIME OF PHOTOINDUCED SPACE-CHARGE FIELDS IN MULTIDOMAIN FERROELECTRIC-CRYSTALS

We demonstrate that the amplitude and lifetime of optically induced sp ace-charge gratings can be dramatically increased in ferroelectric bar ium titanate by partially depoling the crystal prior to grating record ing. By repoling the crystal this space-charge grating produces a refr active index grating capable of diffracting light much more than a gra ting created in a well-poled, single-domain crystal. This effect is ex plained in terms of an electric compensation of free charge by the bou nd charge of the ferroelectric domain walls.