The photovoltaic current density in crystals without a center of symmetry depends bilinearly on the components of the light polarization vector via a third-rank tensor. For LiNb0,:Fe and LiNbO,: Cu the tensor properties are confirmed and three of the four non-vanishing components determined. The dependence on impurity concentration and on photon energy is also investigated.

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Solutions of poly(methyl methacrylate) in styrene are used to produce thin polymer films (1 ym -20 ym) saturated with styrene monomer. In the illuminated areas refractive iindex changes up to 10 -2 are achieved by photoinduced polymerisation. The index patterns may be fixed by annealing treatments removing the residual monomer.

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