This paper describes the experimental and theoretical studies of an anomalous optical beam deflection phenomenon based on electrooptic effect and space-charge-controlled electrical conduction. In the experiment, a large deflection angle of 250mrad (=14.3°) has been observed by applying ±250V to a 0.5-mm-thick KTa1−xNbxO3 crystal with a short interaction length of 5.0mm. The crystal has a rectangular shape with uniform electrodes and there is no prism shape involved which is a common geometrical shape of crystal, electrode, or ferroelectric domain in the conventional electro-optic deflectors. The operating principle is investigated and it is found that the space-charge-controlled electrical conduction in the crystal plays an essential role in this deflection phenomenon. The electrical conduction is carried by electrons injected from the Ohmic contact of the electrode with the crystal. The injected electrons induce the space-charge effect and the electric field becomes nonuniform between the electrodes. The theoretical analysis shows that the electric field has a square-root dependence on the distance from the cathode. As a result, a linearly graded refractive index is induced by the electrooptic Kerr effect of the crystal and the optical beam is cumulatively deflected as it propagates in the crystal. We named this effect the “space-charge-controlled electro-optic effect” and the factors related to the onset of this effect are also discussed.

An electro-optic beam deflector with unprecedented performance is demonstrated. A full deflection angle of 250mrad (=14.3°) has been achieved by applying only ±250V to a 0.5-mm-thick KTa1−xNbxO3 crystal with a short interaction length of 5.0mm. The operating principle is investigated and the origin of the deflection phenomenon is attributed to a nonuniform electric field induced by space-charge-controlled electrical conduction in the crystal.

We propose a new beam scanning model that is applicable to electrooptic materials with electron traps. With this model, we can achieve both high-speed operation and wide-angle scanning, because the operating speed is limited not by the electron mobility but by the frequency limit of the electrooptic effect of the materials. The voltage dependence of the scanning angle at 100 kHz using a KTa1-xNbxO3 crystal is consistent with the property predicted by the proposed model.

The relaxor-like dynamics of the cubic-tetragonal ferroelectric phase transition was studied by Brillouin and Raman scattering in K(Ta 1Àx Nb x)O 3 (KTN) crystals with x ¼ 0.40 (KTN40). The local symmetry breaking by the polar nanoregions (PNRs) was observed in a paraelectric phase by Raman scattering on the A 1 (z) mode of the PNRs with R3m symmetry. Upon cooling from a high temperature, the remarkable increase in the LA phonon damping starts at 45 K above the cubictetragonal phase transition temperature of T C-T ¼ 308 K, which is defined as the intermediate temperature, T* $ 353 K, indicating the start of the rapid growth of the PNRs. The coupling between the LA mode and fluctuation of the PNRs caused a remarkable elastic anomaly in the vicinity of T C-T. The analysis of the temperature dependent central peak shows a critical slowing down towards T C-T , which is the evidence for the order-disorder nature of a ferroelectric phase transition. The evolution of the dynamic PNRs is discussed by the estimation of their length scale, and it is found that it starts to increase near T* and gradually grows towards T C-T. V

We fabricated cylindrical varifocal lenses with fast responses by using the strong Kerr effect of KTa(1-x)Nb(x)O(3) (KTN) single crystals. We observed focus shifts of up to 87 mm with the assistance of a 250 mm focal length lens, which corresponds to a focus shift from infinity to 720 mm by the KTN lens itself. The response time was as fast as 1 μs. We also present a simulation method for calculating refractive index distributions in KTN single crystals, which is essential when designing the lens. The method is characterized by the strain contribution, which has not conventionally been typical of electro-optic simulations. We used this method to explain the refractive index modulations that are characteristic of the varifocal lenses.