Abstract The dynamic response of polar nanoregions under an AC electric field was investigated by measuring the frequency dependence of the quadratic electro-optic (QEO) effect in a paraelectric KTa 0.61 Nb 0.39 O 3 single crystal near the para-ferroelectric phase boundary (0 °C < T - T c < 13 °C). The QEO coefficient R 11 − R 12 reached values as large as 5.96 × 10 −15 m 2 /V 2 at low frequency (500 Hz) and gradually decreased to a nearly stable value as the frequency increased to 300 kHz. Furthermore, a distortion of the QEO effect was observed at low frequency and gradually disappeared as R 11 − R 12 tended towards stability. The giant QEO effect in the KTa 0.61 Nb 0.39 O 3 crystal was attributed to the dynamic rearrangement of polar nanoregions and its anomalous distortion can be explained by considering the asymmetric distribution of polar nanoregions.
Terahertz (THz) quasi-optical devices are typically used for realizing THz full-band modulation. However, the development of THz electronically controlled devices is limited by inadequate transparent electrode materials and inefficient processing technology. In this study, we introduced a novel scheme based on a novel transparent electrode poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) film for realizing THz quasi-optical devices. The ultraviolet (UV) lithography lift-off process is typically used for manufacturing patterned electrodes. Combined with the electronically controlled birefringence characteristics of the liquid crystal in the THz band, the phase of each electrode pixel can be continuously tuned. We experimentally investigated the lithography process of the PEDOT:PSS film with a precision of 10 μm and etched electrode rings with equal spaces. Furthermore, the refractive index of the liquid crystal can be electrically controlled to achieve an approximate parabolic distribution. Thus, the THz beam was focused. The tunable zoom of the THz beam was realized at a distance of 5–20 cm. The intensity of the spot center was magnified 1.38 times, whereas the effective radius decreased 0.51 times. In this study, novel THz transparent electrode materials and a patterning process were proposed for the development of THz quasi-optical devices.
In order to obtain the sheet metal anisotropy under wide strain range, plane strain compression method with laminated samples is investigated. In the experiments, two laminated samples are introduced, sample 1 is deformed at rolling and thickness direction, and sample 2 is deformed at rolling and transverse direction. In the paper, the ratio of deformation forces obtained from sample 2 (p 2 ) to sample1( p 1 ) is used to assess the anisotropy of sheet metal, and verified by analytical method. The results show that the ratio of p 2 top 1 is the function of anisotropic index r, and the anisotropic assessment by this method has a good agreement with that obtained by universal uniaxial tensile test at uniform deformation.
Abstract An electric field controlled two-dimensional higher order diffraction optical beam splitter has been realized based on a photorefractive higher order diffraction grating. In experiments, the splitter was produced by wave coupling (632.8 nm, 532.0 nm) at a small incident angle with a potassium lithium tantalate niobate single crystal. In the process of splitting, the incident beam of different wavelengths (632.8 nm, 532.0 nm) could be split into multi-output beams by the splitter. The influence of an externally applied electric field was studied and results show that the intensity of higher order diffraction could be controlled by the electric field. The polarization properties of higher order diffraction were discussed. An electric field controlled five–three optical beam splitter was investigated theoretically. Keywords: higher order diffractionquadratic electro-optic effectoptical beam splitter Acknowledgements This research was supported by the Development Program for Outstanding Young Teachers in Harbin Institute of Technology (HITQNJS.2008.028), Heilongjiang Postdoctoral Financial assistance (LBN-Z08152), and the China Postdoctoral Science Foundation (20080440895).
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