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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The extraordinary refractive index profile of proton‐exchanged LiNbO3 waveguides as well as the proton and lithium distributions are investigated. The exchange is effected by pure benzoic acid and with lithium benzoate as an additive, on pure and magnesium doped LiNbO3 substrates. The refractive index profiles are reconstructed from measured effective indices by a very reliable improved inverse WKB procedure. Marked deviations from step‐function‐type profiles are found. The same holds for the lithium distribution which has been determined by SIMS. To check the reconstruction procedure, the waveguiding layer is gradually polished off, and the modes of the remaining guide are measured and fitted. Simultaneously, the infrared absorption by OH‐ stretching vibrations is recorded. Its cross section is determined to be (4 ± 2) × 10−19 cm2. The effect of adding lithium benzoate, of doping with magnesium as well as annealing, on the stability of the refractive index profile is discussed.

Volume phase holograms in a n electrooptic crystal like LiNbO, must be fixed so that they are not destroyed upon reading. By heating up the crystal mobilized ions may partially eompensetc the electronic space charge field, and a subsequent development procedure fixes the hologram. A general theory of this t'hermal fixing process is developed and applied to ZiNb0,:Cu. Charge transport by the photovoltaic effect, by drift in a space charge field and by diffusion is taken into account. It is unlikely that mobile protons alone are responsible for the fixing effect. Volumenphasenhologramme in einem elektrooptischen Kristall wie LiNbO, miissen fixiert werden, so daR sie nach dem Lesen nicht zerstort werden. Die durch Aufheizen der Kristalle mobilisierten lonen konnen partiell das elektronische Raumladungsfeld kompensieren und ein darauffolgendes Entwicklungsverfahren fixiert das Hologramm. Eine allgemeinc Theorie dieses thermischen Fixierungsprozesses wird aufgestellt und auf LiNbO,: Cu angewendet. Ladungstransport durch den pliotovoltaischen Effekt, durch Drift in einem Raumladungsfeld und durch Diffusion werden berucksichtigt. Es ist unwahrscheinlich, da13 bewegliche Protonen allein fur den Fixierungseffekt verantwortlich sind.

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